Ch.1-2_Smil, V. (2017). Energy: A Beginner's Guide (2nd ed.)
Summary
The Evolution and Misconceptions of Energy: From Aristotle to Modern Science
The concept of energy has been a part of philosophy for centuries. However, the term itself was coined by Aristotle, who defined it as movement related to an object's function. Later, scientists like Thomas Young defined energy as the product of a body's mass and the square of its velocity, while the Encyclopædia Britannica defined it as "the power, virtue, or efficacy of a thing." Today, energy is often confused with power and force, and is used loosely in popular discourse to describe any number of animated or vigorous actions or experiences. While the concept of energy remains widely misunderstood, scientific study has led to a better understanding of its origins and abstracts.
The Development of Modern Energy Science: From Newton to Joule
The development of modern Energy science began in the 17th century and advanced significantly during the 18th century with the adoption of Isaac Newton's physics and engineering experiments, particularly those associated with James Watt's steam engines. In the early 19th century, Sadi Carnot set down the universal principles applicable to producing kinetic energy from heat, and Justus von Liebig offered a correct interpretation of human and animal metabolism. Julius Robert Mayer formulated the law of the conservation of energy, and James Prescott Joule found the correct value for the equivalence of heat and mechanical energy.
The Law of Thermodynamics and the Universal Tendency Towards Heat Death
Joule's experiments on the mechanical energy invested in churning water were accurate to within one percent. The law of conservation of energy, now known as the first law of thermodynamics, states that energy cannot be created or destroyed. In 1850, Clausius proved that the maximum performance obtainable from an engine depends solely on the temperatures of the heat reservoirs. He coined the term entropy to describe the degree of disorder in a closed system, and formulated the second law of thermodynamics: the entropy of the universe tends to maximum, meaning that useful energy can only decline in a closed system. Heat occupies a unique position in the hierarchy of energies, as it can be completely converted to other forms, but their conversion into other forms can never be complete. C.P. Snow famously described the second law of thermodynamics as the universal tendency toward heat death and disorder.
The Fundamentals of Energy: From Thermodynamics to Mass-Energy Conversion
The text summarizes the fundamental concepts of energy, including its definition, conversion, and efficiency, and the laws of thermodynamics that govern it. It explains how living organisms violate the second law of thermodynamics by creating more ordered and complex forms of life, and how the third law of thermodynamics explains the limit of all processes at absolute zero temperature. Additionally, the text discusses the relationship between mass and energy, as well as the conversion of mass into energy in nuclear reactors. Despite the complexity of the topic, the author emphasizes the need to make the abstract concept of energy more accessible to the general public.
The Many Forms of EnergyEnergy is the capacity for doing work, and it can take many forms, from physical exertion to metabolic processes in the body. Even thinking hard about an abstract concept uses energy, but it is negligible compared to the energy used by the brain while sleeping or during physical activity. Energy is an abstract concept that covers a variety of natural and human-generated phenomena, including heat, motion, light, and chemical energy.
The Various Forms and Conversions of Energy
The text discusses different forms of energy and their conversions, including electromagnetic, chemical, thermal, electrical, and nuclear energies, as well as kinetic energy. It highlights the importance of potential energy, which results from a change in the spatial setting of a mass or its configuration. Examples of potential energy include water stored behind a dam and a rock precariously poised on a weathering slope. The text also notes that the magnitude of kinetic energy depends on the square of an object's velocity, and that even small objects can become dangerous at high speeds.
Understanding Energy Conversion and StorageElastic potential energy is stored in springs and released as useful work. Biomass and fossil fuels are stores of chemical energy that release heat through combustion. Heat is produced by several energy conversions such as nuclear fission, friction and conduction, convection, and radiation. Latent heat is the amount of energy needed to effect physical changes with no temperature change.
The Efficiency of Energy Conversion: Photosynthesis vs. Machines
The efficiency of energy conversion depends on the amount of desirable output compared to initial input. Photosynthesis is inefficient, converting only 0.3% of incoming sunlight into plant mass. In contrast, some machines can convert energy with 99% efficiency.
The Significance of Système International (SI) Units in Measuring Energy and Power
The Système International (SI) units are still in use today. The SI has seven fundamental measures: length, mass, time, electric current, temperature, amount of substance, and luminous intensity. The units are used to derive more complex quantities, including force, pressure, energy, and capacitance. Energy is expended when a force is exerted over a distance, and power is the rate of energy use. The SI has over twenty derived units, including all energy-related variables, with special names and symbols.
Exploring Measurement Units and Power Density: Assessing Energy Flows in Various Phenomena
The text discusses various units of measurement in the SI system, including units of length, mass, time, electric current, temperature, and amount of substance. It also introduces the concept of power density, which measures the rate of energy flow per unit area. The text emphasizes that power density can be used to assess the energy flows of various phenomena, from solar radiation to household energy use. Finally, the text provides an example of how power can be used to assess the energy required to lift an object.
The Energy Consumption Gap: Humans vs. the Sun
The amount of energy consumed by humans and other living organisms is relatively small compared to the amount of energy received from the sun. In 2015, the global consumption of all fossil fuels was equivalent to only about 0.009 percent of the planet's received solar radiation.
The Power Range of Passenger Cars: From 90 to 120 kW
The power of passenger cars ranges from 90 to 120 kW, with the Koenigsegg Regera reaching up to 1.1 MW.
The Importance of Understanding Calorie Units and Electrical Measurements
The recommended daily calorie intake for a healthy adult male with a healthy body mass index is around 2,500 calories, not 2,500 small calories, which is a mistake often made by nutritionists. In contrast, a twenty-gram mouse requires at least 3,800 calories per day for its basal metabolism, highlighting the difference between calorie units. The voltage in an electrical circuit is measured in volts and depends on the difference in electrical potential between the positive and negative terminals of a battery. The resistance encountered by a current is measured in ohms and depends on the conducting material and its dimensions, with copper being a better conductor than aluminum or iron. Finally, Ohm's law relates voltage, resistance, and current in DC circuits, but has to be modified for AC circuits to account for reactance.
Understanding the Relationship Between Voltage, Current, and Resistance in ElectricityThe relationship between voltage, current and resistance is crucial for understanding how electricity works and for using it safely. Ohm's law states that current is directly proportional to voltage and inversely proportional to resistance. Touching a live wire with dry hands is usually not lethal, but wet skin can provide a low-resistance conductor for lethal currents. The choice of voltage and current depends on the desired power output, and AC is preferred for long-distance transmission and distribution due to lower transmission losses.
The Battle Between Direct Current and Alternating Current: AC Emerges Victorious
The battle of systems between direct current (DC) and alternating current (AC) was basically over by 1890, with AC winning due to its more reliable transformers, AC motors and meters, and rotary DC-to-AC converters.
The Search for Life in the Universe: Challenges and Lack of Discoveries
The search for life in the universe is difficult due to the specific requirements for habitability, such as having a suitable star and planet with the correct conditions for supporting complex organisms. So far, no signs of life have been discovered beyond Earth.
The Earth's Atmosphere and Its Vital Role in Supporting Life
The Earth's atmosphere traps some of the incoming solar energy, raising the planet's average temperature to support life.
The Vital Role of Solar Energy in Sustaining Life on Earth
The sun produces vast amounts of energy through nuclear fusion, which is mostly converted into light and heat. This energy reaches the Earth's atmosphere and is distributed across the spectrum of colors, with maximum emission in the green part of the spectrum. The sun's energy is essential for all life on Earth, and its radiation is the primary source of energy for photosynthesis in plants.
The Brightness and Composition of Visible LightThe text explains that the human eye has peak sensitivity for green and yellow light, with maximum visibility at 556 nm. Visible light carries about 38% of the energy of incoming solar radiation, and the radiation that we receive on the ground differs greatly from the radiation at the top of the atmosphere in terms of both quantity and spectral composition. The average insolation amounts to almost exactly half of the solar constant, averaged per unit area of the rotating Earth, or approximately 170 W/m².
Unleashing Solar Power: Overcoming Challenges for Affordable Electricity
Solar radiation provides enough energy to power a civilization consuming 100 times more energy than our current one, but converting it into affordable electricity is challenging. The equatorial zone and parts of Asia receive less sunlight annually than New England due to cloud cover. The peaks of noon summer insolation are virtually identical in Jakarta and Edmonton. The Earth's radiation balance is maintained through the latent heat of evaporated water, and atmospheric water vapor is the most important greenhouse gas. The greenhouse effect has maintained a stable biospheric temperature for 3.5 billion years, with feedbacks between atmospheric CO₂, temperature, and silicate weathering playing a key regulatory role.
Understanding the Causes and Effects of Climate Change
Climate change is caused by CO₂ emissions from burning fossil fuels and deforestation, leading to concerns about the increased greenhouse effect. The absorption of radiation from the sun powers the global atmospheric circulation, which distributes heat, water vapor, and energy, driving weather patterns and creating the trade winds. The circulation is also influenced by polar and mid-latitude cells, and the formation of cyclonic winds in summer.
The Power of Tropical Storms: Hurricanes, Typhoons, and Tornadoes
Hurricanes and typhoons are powerful tropical storms that can cause widespread damage. They form over warm ocean waters and move westward, affecting large parts of the Americas and Asia. In contrast, tornadoes are smaller and less powerful but can still cause significant damage with their high winds and short paths.
The Impact of El Niño on Weather Patterns: Heavy Rains in Peru and Drought in Australia
The El Niño phenomenon in the Pacific Ocean causes warm surface waters to expand westward, leading to heavy rains in Peru and drought in Australia.
The Earth's Internal Heat: Shaping Life and CivilizationsThe Earth's internal heat is constantly re-shaping the planet through geological processes, and while it is less significant than solar radiation, its impact on the evolution of life and civilizations has been significant. The total global heat flow from the Earth's interior is estimated to be around 44 terawatts, with the youngest ocean floor oozing heat at the highest rate.
The Earth's Tectonic Plates: Drivers of Earthquakes, Volcanoes, and Geological Features
The Earth's tectonic plates move slowly, with the fastest moving Pacific plate traveling at a maximum speed of 90 km per million years. This movement causes earthquakes and volcanic eruptions, as well as the formation of mountain ranges and deep ocean trenches. The energy driving this process comes from the Earth's mantle, and is distributed through the planet's geological features.
The Power and Impact of Earthquakes: A Closer Look
Earthquakes are a powerful natural phenomenon that occurs when there is a sudden release of energy in the Earth's crust. Most earthquakes take place in the Pacific's coastal areas, known as the "Ring of Fire". The energy released by earthquakes is small compared to the total geothermal flux, but the destructive power of larger earthquakes is significant. In the 20th century, earthquakes caused more deaths than volcanic eruptions, cyclones, and floods combined. The Richter magnitude scale measures the energy of an earthquake, and the largest recorded earthquakes release nearly 1.5 EJ of energy. However, there is no strong correlation between the power of an earthquake and the death toll, which is mainly determined by residential density and housing construction quality. The most deadly earthquake in recent history was the 1976 Tangshan earthquake in China, which killed officially 242,219 people, but the real toll was much higher. Some underwater earthquakes generate tsunamis, huge sea waves that can travel at speeds of more than 600 km/h and strike shoreline vegetation and structures with great force.
The Catastrophic Power of Earthquakes and Volcanoes: Devastation and Destruction Unleashed
A massive earthquake with a magnitude of 9.0 struck off the coast of Sumatra on December 26, 2004, triggering a tsunami that resulted in more than 200,000 deaths in the region. The release of geothermal energy from volcanic eruptions is relatively small compared to other sources, but it can still be devastating, as seen in the eruption of Mount St. Helens in 1980 and the 1883 eruption of Krakatoa. Volcanic heat is carried by ash clouds or slow-moving lava flows, and the most dangerous form is pyroclastic flows, which can travel at speeds of over 100 km/h and smother everything in their path.
Mega Eruptions, Massive Lava Flows, and Magma Plumes: Unveiling Earth's Powerful Forces
The Yellowstone eruption 2.2 million years ago released an estimated 2,500 km³ of ash, while the Deccan Traps in west central India were formed by one million cubic kilometers of basalt lava over 5 million years. The Hawaiian Islands and Virunga volcano chain were created by hot magma plumes piercing through tectonic plates. The process of photosynthesis is energized by light absorbed by pigments in chloroplasts, but its efficiency is low.
Photosynthetic Pathways: Understanding Energy Conversion and Efficiency
Photosynthetic paths involve three enzyme complexes that convert light energy into chemical energy, resulting in the production of NADP and ATP. The most common path is the reductive pentose phosphate cycle, which catalyzes the conversion of carbon dioxide into carbohydrates. A counterpart of photosynthesis, the photorespiration cycle, can reconvert carbon and reduce net efficiency. Some plants use the C/C, cycle, which has inherently low energy conversion efficiencies and demands more water. Another path involves hydration of CO2 to bicarbonate, followed by reduction with PEP to produce oxaloacetate.
The Comparative Efficiency of C3, C4, and CAM Photosynthetic Paths
The C3 photosynthetic path is the most common among plants, while the C4 and CAM paths are less common. C4 and CAM plants are more efficient in hot and dry conditions, while C3 plants are better adapted to cooler temperatures and higher rainfall. The CAM path is restricted to succulents and some orchids and bromeliads, and involves absorbing CO2 at night and converting it into malate for use during the day. Commercially important CAM plants include pineapple, aloe, opuntia, and agave.
Understanding the Main Concern: CO2 Emissions and Climate Change
The increase in CO2 emissions caused by human activities, particularly burning fossil fuels and deforestation, is the main concern regarding climate change.
The Power and Destruction of Hurricanes and Tornadoes
Hurricanes are powerful storms that form over warm ocean waters and can cause massive destruction. Tornadoes, on the other hand, are smaller and shorter-lived but can still be incredibly destructive.
The Unique Properties of Water and Its Impact on Global Temperatures
The unique properties of water include its high density at 3.98°C, which allows fish to survive in cold northern waters, and the way it transfers energy through latent heat and kinetic energy. Ocean currents and upwelling zones also play a role in regulating global temperatures.
The Earth's Heat: Recreating Ocean Floor and Reshaping Continents
The Earth's heat is constantly recreating the ocean floor and re-assembling and splitting the continents, with the Pacific plate being the largest. The heat is mainly from radioactive decay, with a global power of 44TW, and a mean global flow of less than 90mW/m². The Pacific plate is purely oceanic and can be less than 10 km thick, while other plates can have piggy-backing continents and crustal thicknesses of more than 100 km. The spreading rate is about 3 km per year.
The Constant Movement and Recycling of the Earth's Crust
The Earth's crust is made up of several large plates that move slowly and constantly. The movement of these plates is driven by the Earth's mantle, a layer of solid rock between the crust and the liquid core. The plates move apart at mid-ocean ridges, creating new ocean floor, and collide along subduction zones, causing earthquakes and volcanic eruptions. The energy from these processes is responsible for the continuous recycling of the Earth's crust.
The Power and Impact of Earthquakes: From Energy Release to Casualties
Earthquakes are a powerful force of nature that can cause significant damage and loss of life. Most earthquakes occur in the Pacific's coastal areas, known as the "Ring of Fire," and are measured using the Richter scale. The largest earthquakes can release nearly 1.5 EJ of energy, which is equivalent to 50 PW. However, the power of an earthquake does not necessarily correlate with the death toll, as residential density and building construction quality play a significant role in the number of casualties. The most deadly earthquake in recent history was the Tangshan earthquake in 1976, which killed an estimated 242,219 people in China's Hebei province. Some underwater earthquakes can also generate tsunamis, which are massive sea waves that can travel at speeds of more than 600 km/h and cause significant damage to coastal areas.
The Devastating Tsunami of 2004: Unleashing the Power of Subduction
A massive earthquake with a magnitude of 9.0 occurred off the coast of Sumatra on December 26, 2004, triggering a destructive tsunami that caused more than 200,000 deaths. The earthquake was caused by subduction, the process by which one tectonic plate sinks beneath another, and was the most destructive tsunami in recent history.
The Enormous Volcanic Eruptions and Surprising Secrets of Photosynthesis Unveiled
The Yellowstone eruption 2.2 million years ago released an estimated 2,500 km³ of ash, while the Deccan Traps in west central India were formed by about one million cubic kilometers of basalt lava over five million years. The Hawaiian Islands and Virunga volcano chain are examples of hot spots creating volcanic activity far away from subduction or collision zones. The conversion of simple inorganic inputs into new phytomass in photosynthesis is surprisingly low, and the key sequential steps were revealed by Melvin Calvin in 1948.
The Complex Process of Photosynthesis: From Light Energy to Carbohydrates
Photosynthesis involves the conversion of light energy into chemical energy, which is stored in carbohydrates. The process involves three main steps: the absorption of light energy by pigments, the conversion of carbon dioxide into carbohydrates, and the production of ATP and NADPH, which drive the incorporation of carbon into carbohydrates. The most common photosynthetic pathway is the Calvin-Benson cycle, which involves the addition of carbon dioxide to a five-carbon molecule to form a three-carbon molecule, followed by the regeneration of the original enzyme and the use of the triose phosphate to form carbohydrates or fatty acids. However, this process can be inefficient due to the presence of oxygen in the atmosphere, which can bind to the enzyme responsible for adding carbon dioxide, leading to the production of glycolate and a reduction in net efficiency. Other photosynthetic pathways exist, but they are less common and have lower energy conversion efficiencies.
The Efficiency and Adaptability of Photosynthetic Paths in Plants
Plants use different photosynthetic paths to capture carbon dioxide, each with varying levels of efficiency. The C4 path is more efficient than the C3 path because it relies on a better enzyme and lower oxygen levels. C4 plants also have higher net photosynthetic rates at higher temperatures and are more water-efficient than C3 plants. However, only three major crops follow the C4 path, and it is also shared by some invasive weeds. The final path, CAM, is restricted to succulents and is an adaptation to extreme aridity and high temperatures. The energy obtained through respiration is used to maintain basic functions and make complex organic compounds needed by organisms for their metabolism and defense against herbivores.
The Impressive Quantity and Quality of Photosynthetic Performance
Photosynthesis is an inefficient process, with only a small percentage of incoming solar energy being converted into new plant matter. The global average is less than 0.2%. However, the overall photosynthetic performance is impressive in terms of quantity and quality. The best estimates show an annual net primary production of 120 billion tonnes on the continents and 110 billion tonnes in the ocean. Major biomes are limited by temperature and precipitation, not insolation. The rates of NPP range widely for different ecosystems, from 1-3.5 kg/m² in tropical rainforests to 0.2-1.5 kg/m² for most grasslands. Despite their lower productivity, temperate forests can store much more wood per hectare than their tropical counterparts.
The Impact of Wood Composition on Heating Value and Crop Yield
The heating value of different woods depends on their lignin and extractives content, with higher values for those with more lignin and resins. The range for common North American species is from 17.8 MJ/kg for sweetgum to 21 MJ/kg for Douglas fir. NPP rates are essentially equal to annual yields for crops that have not suffered any major damage from pests and diseases. Leguminous crops yield mostly less than two tonnes per hectare, while vegetables can produce up to 50 t/ha. Well-managed forests have annual increments of between 1 and 2 t/ha of dry matter.
The Determinants of Basal Metabolic Rate in Mammals
The basal metabolic rate (BMR) of mammals is measured at complete rest, several hours after the last intake of any nutrients, and in a temperature-regulated setting. Oxygen consumption (or CO2 generation) served for decades as its best determinant. In 1932, Max Kleiber noted that the basal metabolic rates of mammals depended only on their body weight raised to the power 0.75. The exponent is considerably higher for carnivorous mammals, and much lower for desert rodents, an adaptation that minimizes their energy needs in a hostile environment. Endotherms (vertebrates that actively maintain their core body temperature) must pay for their thermoregulation by having a BMR as much as 20-40 times higher than similar ectotherms.
The Relationship between Body Mass and Basal Metabolic Rate in Animals
The basal metabolic rate (BMR) of animals declines exponentially with increasing body mass, with smaller endotherms having higher BMRs relative to body weight, and larger endotherms having lower BMRs. The smallest shrew needs about 100 mW/g, while a steer requires only 1mW/g. The relationship between BMR and body weight is known as Kleiber's line. Energy expenditure for some activities, such as flying or swimming, is a multiple of BMR, while others require only a modest multiple. Mammals have an average metabolic scope of about ten, while birds have a higher scope of about fifteen.
Insights into Animal Locomotion: Running, Swimming, and Flying
The text discusses the different forms of locomotion in animals, including running, swimming, and flying. It explains that running is the most energy-demanding way to move, and that size matters when it comes to speed and endurance. The text also highlights the importance of food sources during long-distance migrations, and notes that some birds can fly non-stop for thousands of kilometers, guided by various cues.
The Hierarchical Flow of Energy in Ecosystems
The summary of the text is that energy flows through ecosystems in a hierarchical manner, with autotrophs at the top and decomposers at the bottom. The more steps removed a living thing is from the primary energy of the Sun, the less energy is available at the successive feeding levels. Omnivory is common in nature, and humans have mastered this approach by consuming a wide variety of foods. In most ecosystems, the feeding cascades are short, with secondary consumers being the most abundant.
The Complexity of Marine Ecosystems: From Phytoplankton to Predatory Fish
Marine ecosystems are complex and diverse, with phytoplankton forming the base of the food chain and large predatory fish at the top. The pyramid-shaped distribution of biomass in terrestrial ecosystems is inverted in the ocean, where heterotrophs may outweigh autotrophs. Some exceptions include filter-feeding whales and sharks, which consume large quantities of zooplankton and phytoplankton. The decline in heterotrophs in higher trophic levels is associated with increasing body size, and herbivory has energetic advantages.
The Factors Influencing Efficiency of Energy Transfer in Ecosystems
The efficiency of energy transfer in ecosystems is influenced by factors such as exploitation, assimilation, and production. Herbivores typically consume 1-60% of available phytomass, while carnivores rarely exceed 10%. Assimilation efficiencies are low for herbivores and high for carnivores, while production efficiency is much higher among ectotherms. Trophic efficiency ranges from a small fraction of one percent for birds to 30% for insects, and shows little correlation with taxonomic or ecosystemic factors.
The Evolution of Energy Use in Human History
Human history has been characterized by the use of energy for survival, beginning with muscle power and simple tools, followed by the domestication of animals and the invention of complex machines. The use of fire, bows and arrows, and fishing nets were also significant milestones.
Notes
The Evolution of the Concept of Energy
Aristotle coined the term "energeia" in his Metaphysics, relating it to movement and actuality.
The understanding of energy remained unchanged for nearly two millennia, with faulty concepts persisting even in modern science.
In 1807, Thomas Young defined energy as the product of mass and velocity, but his formula was inaccurate.
The seventh edition of the Encyclopedia Britannica in 1842 offered a brief and unscientific definition of energy.
Energy is often misused and confused with power and force in popular discourse.
Physical fitness enthusiasts claim to feel energized after exercise, but it is actually a result of the release of endorphins in the brain.
Informed writing should have well-defined terms and avoid sloppy use of ingrained terms.
Development of Energy Studies and Conservation of Energy
Theoretical energy studies achieved coherence and clarity by the end of the nineteenth century.
Western intellectual and inventive activity in the eighteenth and nineteenth centuries laid the foundations of modern Energy.
Isaac Newton's comprehensive view of physics and James Watt's improvements of steam engines greatly contributed to the advances in energy studies.
Sadi Carnot set down universal principles for producing kinetic energy from heat and defined the maximum efficiency of a heat engine.
Justus von Liebig offered a correct interpretation of human and animal metabolism by linking it to the oxidation of foods.
Julius Robert Mayer's observation of brighter blood in the tropics led him to the concept of heat and work equivalence, which led to the formulation of the law of conservation of energy.
Mayer published the first quantitative estimate of energy equivalence and extended the concept to all natural phenomena.
James Prescott Joule conducted experiments to determine the correct value for the equivalence of heat and mechanical energy.
Concepts and Measures in Thermodynamics
In 1847, Joule's experiments accurately measured the mechanical energy invested in the churning process of water using an assembly of revolving vanes driven by weights.
The law of conservation of energy, known as the first law of thermodynamics, states that energy cannot be created or destroyed.
In 1850, Clausius published a paper on the mechanical theory of heat, proving that the maximum performance of an engine using the Carnot cycle relies on the temperatures of the heat reservoirs.
Clausius coined the term entropy in his 1865 paper, defining it as the degree of disorder in a closed system.
The second law of thermodynamics states that the entropy of the universe tends to maximum, meaning that in a closed system, the availability of useful energy can only decline.
Heat occupies a unique position in the hierarchy of energies, as it can be completely converted to other forms but its conversion into other forms can never be complete.
The second law of thermodynamics, which describes the universal tendency toward heat death and disorder, is often unknown to non-scientists.
C. P. Snow famously highlighted the lack of scientific literacy among educated individuals in his 1959 lecture, emphasizing the importance of understanding the Second Law of Thermodynamics.
The Laws of Thermodynamics and the Concept of Energy
The second law of thermodynamics is often violated by living organisms, which create more ordered and complex forms of life through growth and evolution.
However, this does not conflict with the second law, as it only applies to closed systems in thermodynamic equilibrium, while the Earth's biosphere is an open system that constantly imports solar energy and reduces entropy.
The third law of thermodynamics states that all processes stop and entropy does not change near absolute zero temperature.
In 1905, Albert Einstein extended the first law of thermodynamics by stating that mass is a form of energy, as expressed in the equation E=mc².
One kilogram of uranium-235 can release an amount of energy equivalent to 190 tonnes of crude oil through nuclear fission.
Despite our extensive scientific knowledge, the concept of energy remains elusive, as stated by Richard Feynman in his lectures on physics.
Fundamental Concepts: Energies, Conversions, Efficiencies
Energy defined as the capacity for doing work, beyond mechanical exertion
Energy applied to any process that produces a change in an affected system
Even in motionless state, metabolism performs work to power bodily functions
Thinking hard about abstract concepts increases energy use negligibly
Different forms of energy and conversions lead to various work accomplishments
Lightning converts electrical energy to electromagnetic, thermal, and chemical energy
Motors of stacking cranes convert electrical energy to mechanical and potential energy
Energy is an abstract concept covering various natural and human-generated phenomena
Commonly encountered forms of energy include heat, motion, light, and chemical energy
Energy Conversions and Manifestations
Some conversions of energy are essential to life, such as photosynthesis converting electromagnetic energy into chemical energy in plants.
Cooking and heating involve converting chemical energy in biomass or fossil fuels to thermal energy.
Chemical energy is converted to electrical energy in batteries, powering mobile phones, music players, and radios.
The conversion of electromagnetic energy to nuclear energy through gamma-neutron reactions is used for specialized scientific and industrial tasks.
Kinetic energy is associated with moving masses and depends on velocity squared.
Tornado winds and space debris at high speeds can cause significant damage due to their kinetic energy.
Potential energy results from a mass's change in spatial setting or configuration.
Gravitational potential energy is common and can be used to generate electricity, such as water stored behind dams.
Various Forms of Energy and Heat: Notes on Potential Energy, Chemical Energy, and Heat Transfer
The potential energy of water or a rock is determined by its elevated mass, mean height above ground (h), and gravitational constant (g).
Wound springs store elastic potential energy, which is released as the coil unwinds, powering devices like watches and toys.
Biomass and fossil fuels are vast stores of chemical energy held in atomic bonds. Combustion releases this energy as heat through rapid oxidation.
Heat of combustion is the difference in energy between initial reactants and newly formed compounds.
Heat can be transferred through conduction, convection, and radiation.
Latent heat is the energy required for a physical change with no temperature change, such as changing water to steam.
Energy Conversion Efficiency and Losses
The total amount of energy released during combustion, with water condensed to liquid, is the first measure of energy released by fuel.
Subtracting the energy required to evaporate water formed during combustion gives the second measure, which is lower.
The difference in energy released is around 1% for coke, 10% for natural gases, and nearly 20% for pure hydrogen.
Wet wood contains high moisture and releases thermal energy into evaporating water rather than warming a room.
Photosynthesis has a low efficiency of converting solar radiation into plant mass, with only 0.3% globally.
High energy loss during low-efficiency conversion means a small part of the input is transformed into a desired product.
Certain processes and machines have efficiencies greater than 90%, such as resistance heaters, digestion of carbohydrates, natural gas furnaces, large electrical motors, and turbines in thermal stations.
All energy phenomena can be quantified using universal units.
Introduction to SI Units and Energy Measurements
In 1960, the Système International d'Unités (SI) was adopted as the standard for scientific and engineering quantifications.
The SI specifies seven fundamental measures: length, mass, time, electric current, temperature, amount of substance, and luminous intensity.
These fundamental units are directly used to measure common variables and derive complex quantities.
Mass, length, and time are the three fundamental variables needed to derive units encountered in energy studies.
Energy's dimensional formula is ML²/T², and power is measured as ML²/T³.
SI units for length, mass, and time are meter (m), kilogram (kg), and seconds (s) respectively.
The unit of force is the newton (N), and the unit of energy is the joule (J).
Energy Concepts and Measurements
Power is the energy flow per unit of time, measured in watts (W), with one watt equaling one joule per second (J/s).
Power density (W/m²) is a revealing measure in energy studies, representing power per unit area.
Power density can be extended to various energy flows, such as food harvests and electricity demand.
Vertical power density is useful for understanding forces per unit of vertical area and their potential damage.
Gravitational acceleration at the Earth's surface is 9.81 m/s², simplified to ten for easier calculations.
Holding a one-kilogram mass one meter above ground results in a force of ten newtons.
Holding a mass one-tenth the size results in a force of one newton.
Raising an object one meter using one joule of energy in one second is a power expenditure of one watt.
Power does not indicate the total amount of energy consumed or released.
A giant lightning bolt and the Earth's geothermal flow have similar power magnitudes, but the lightning is ephemeral while the geothermal flow has been ongoing for billions of years.
Magnitudes of Energy and Power
The solar radiation received by Earth is a continuous energy flow, measured at a rate of 1.73 x 10¹7 W, which delimits most natural processes.
In 2015, the global consumption of fossil fuels amounted to a rate of 15TW, equivalent to 0.009 percent of the planet's received solar radiation.
Basic energy and power units refer to small amounts and rates, with examples such as a single chickpea containing 5,000 J of chemical energy and a vole needing 50,000 J a day to stay alive.
Winds in a thunderstorm can unleash over 100,000,000,000,000 J in less than an hour, with a power of more than 25,000,000,000 W.
Energy studies use prefixes such as kilo, mega, giga, tera, peta, and exa to represent different magnitudes of energy and power.
The net energy content of fuels ranges from eleven MJ/kg to forty-four MJ/kg, while the gross energy content of foods varies from less than one MJ/kg to nearly forty MJ/kg.
Energy Magnitudes and Units
One kilowatt-hour (kWh) is equal to 3.6 million watt-seconds or one thousand watt-hours, and it is commonly used to measure electricity consumption and pricing.
The average American household uses about 1,000 kWh (1 MWh) per month, which is equivalent to having fourteen 100W lights on for thirty days.
Small kitchen appliances and passenger cars have power ratings ranging between 50-500W and 90-120kW, respectively.
Large steam- and water-driven turbo generators in fossil-fueled power plants have capacities between 500 and 1,650 MW.
China's Sanxia (Three Gorges) project, the world's largest, has thirty-four turbines with a combined capacity of 22.5 GW.
Solar radiation averages about 170 W/m², and downtown areas of large cities radiate thermal energy exceeding 50 W/m².
Well-built structures can withstand fluxes below 18 kW/m², while tornadoes and tsunamis can have power densities exceeding 100 W/m².
The commonly used submultiples for energy measurements are milli (m, 10-3), micro (u, 10-6), and nano (n, 10-).
Various examples of power ratings include a laser in a CD-ROM drive (5 mW), a quartz watch (1μW), and a flea's hops (100 W).
Fuels' energy content is often expressed in British thermal units (Btu), work accomplished in foot-pounds-force, power in horsepower (hp), and force in pounds (lb force).
Units of Energy and Electrical Measurements
The calorie is a non-SI unit of energy and is equal to the amount of heat needed to raise the temperature of 1g of water from 14.5 to 15.5°C.
A kilocalorie (kcal) is a 1,000-fold multiple of a calorie and is commonly used in nutrition.
A healthy adult male within the optimum body mass index range will need about 2,500 kcal of food per day.
Nutritionists started using "Cal" to signify a kilocalorie, leading to confusion with the smaller calorie unit.
Eating 2,500 calories a day would not even be sufficient for a twenty gram mouse.
The daily basal metabolism of a mouse requires about 3,800 cal.
The daily basic metabolic rate of a healthy 70 kg adult male is about 7.1 MJ, which can increase with physical activities.
Current is measured in amps (A) and voltage is measured in volts (V).
The resistance encountered by a current is measured in ohms (Ω) and depends on the conducting material and its dimensions.
Copper is a better conductor than aluminum, but aluminum alloys are used for long-distance high-voltage lines due to cost.
Direct current (DC) flows in one direction, while alternating current (AC) constantly changes its amplitude and reverses direction.
Ohm's law relates voltage to resistance and current in DC circuits: V = IR. It needs modification for AC circuits due to reactance.
The Implications of Ohm's Law and AC Transmission in Electricity
Using impedance (Z), Ohm's law is modified to I = V/Z which has implications for transmitting and using electricity safely.
Electric shocks and the risk of electrocution depend on the current that passes through the body.
According to Ohm's law, I = V/R, meaning higher resistance minimizes the current for a given voltage.
Dry skin offers high resistance, limiting the current to safe levels.
Wet skin provides low resistance, allowing lethal currents to pass through.
Touching live wires with sweaty hands increases the risk of electrocution.
Power is determined by the product of current and voltage, and voltage equals current multiplied by resistance (V = IR).
Different resistance values are required for different electrical appliances.
Increasing voltage reduces transmission losses in proportion to the square of V.
AC transmission is favored over DC transmission due to the use of transformers to reduce voltage.
Thomas Edison initially resisted the use of AC transmission but eventually accepted its benefits.
Evolution of Electrical Systems and Batteries
Reliable transformers, AC motors, and meters, along with rotary DC-to-AC converters, played a crucial role in connecting existing DC stations and networks to high-voltage AC lines.
By 1890, the battle of systems between DC and AC was essentially decided, with AC emerging as the future of electrical systems.
Despite the dominance of AC, DC is still prevalent in electrical devices, either converted from AC or supplied by batteries.
DC motors are preferred for electric trains due to their high starting torque.
Portable DC needs are met by different types of batteries that convert chemical energy into electrical energy.
Lead-acid batteries, commonly used in cars, provide 12V through six lead-based cells and sulfuric acid electrolyte.
Small cylindrical batteries for toys, flashlights, etc., are improved versions of Georges Leclanché's carbon-zinc cell, with alkaline batteries introduced in 1959.
Various types of batteries exist, including lithium-ion for laptops and silver oxide button cells for hearing aids and watches.
Conditions for Life on Earth
The probes sent to Mars did not find evidence of life.
Venus is too hot to sustain life.
Other planets in the solar system are unsuitable for life.
Extra-solar planets discovered so far are unlikely to support life.
No indication of life found despite listening to space sounds.
A suitable "Goldilocks" star and planet are necessary for life.
Goldilocks star should not be too big or too small.
Goldilocks planet should have water that is not vaporized or frozen.
Many other prerequisites must be met for a planet to be habitable.
Changing certain attributes of Earth would make it unsuitable for life.
Energy processes and the role of atmosphere and living organisms
The Earth's atmosphere allows incoming radiation to warm the surface but absorbs some outgoing longwave radiation.
Without this absorption, the Earth would be a "perfect black body radiator" and have a temperature of -18°C, making life impossible.
Atmospheric gases selectively absorb and re-radiate outgoing radiation, causing the greenhouse effect and raising the Earth's surface temperature by 33K.
The greenhouse effect is mainly caused by water vapor and CO₂.
This temperature range supports the evolution and diversification of complex life on Earth.
Geothermal energy powers global tectonics and leads to natural phenomena like volcanic eruptions, earthquakes, and tsunamis.
Living organisms use different metabolic pathways to convert energy into living mass.
Autotrophs (primary producers) use electromagnetic energy and nutrients to produce new biomass.
Phototrophs use light to produce energy-rich ATP and convert CO₂ and nutrients into biomass.
Chemotrophs do not require light and use CO₂, oxygen, and specific inorganic compounds for metabolism.
Heterotrophs cannot synthesize biomass and rely on organic compounds for their building blocks.
Energy and the Sun
Heterotrophs are classified into four categories: herbivores, carnivores, saprovores/detritivores, and omnivores.
Energy studies have revealed similarities in plant and animal metabolism and intricate energy flows in ecosystems, including carbon and nitrogen cycles.
The sun belongs to the G2 dwarf category, with most of its power coming from the proton-proton reaction.
The sun's energy production is immense, converting 4.4 Mt of matter into energy every second.
Over four and a half billion years, the sun has consumed just 0.03% of its mass and more than half of the hydrogen in its core.
The solar radiation reaching the Earth's atmosphere is approximately 1367W/m², known as the solar constant, but with irregular and regular fluctuations.
The sun's spectrum closely resembles a perfect black body with maximum emission in the green light wavelengths.
The visible part of the spectrum ranges from deep violet (400nm) to dark red (700 nm).
Human Eye Sensitivity and Solar Radiation
Human eyes are most sensitive to green and yellow light (576-585 nm), with the highest visibility at 556 nm.
Visible light consists of about 38% of the energy from the sun, while less than 9% is in the form of ultraviolet (UV) radiation (less than 400 nm) that humans cannot see or feel.
Fifty-three percent of solar radiation is in the infrared (IR) wavelengths, which includes detectable heat.
The radiation measured at the top of the atmosphere differs from the radiation received on the ground in terms of quantity and composition.
The solar constant measures the radiation that streams through space and is perpendicular to a flat surface. The average amount of this radiation received on Earth's surface is one-quarter (about 342 W/m²) of the extra-terrestrial flow.
Roughly twenty percent of solar radiation is absorbed as it passes through Earth's atmosphere, with UV radiation being absorbed by stratospheric ozone.
The remaining radiation is absorbed by tropospheric clouds and aerosols suspended in the atmosphere.
The global albedo, the share of incoming radiation reflected by clouds and the Earth's surface, is approximately thirty percent.
The average insolation (incoming solar radiation) is about half of the solar constant, averaging around 170 W/m².
The total annual solar energy input is estimated to be 2.7 x 1024 or roughly 87 PW, which is more than five thousand times the worldwide consumption of fossil fuels and primary electricity in 2015.
The fate of civilization depends not on the shortage of energy, but rather on the ability to harness and convert it into useful energy at an acceptable cost.
Implications of Solar Radiation and Greenhouse Effect on Energy Conversion and Climate
Despite a civilization consuming a hundred times more energy than ours, converting solar radiation into affordable electricity remains challenging.
Tropical and monsoonal cloudiness cause solar impoverishment in equatorial zones and northern Asia.
Equatorial Amazonia, southern Nigeria, and provinces in southern China receive less sunlight annually than New England.
Noon summer insolation peaks are identical in Jakarta and Edmonton.
Earth's radiation balance is maintained through conduction, convection, latent heat, and greenhouse gases.
Waters vapor, CO₂, methane, nitrous oxide, and ozone contribute to the greenhouse effect.
Changing atmospheric concentrations of water vapor amplify temperature changes.
Feedback between atmospheric CO₂, temperature, and silicate weathering regulate climate.
The Role of CO₂ in Climate Concerns and the Dynamics of Atmospheric Circulation
CO₂ emissions from combustion of fossil fuels and deforestation are the main causes of concerns regarding climate change.
Absorbed radiation from CO₂ heats continents and oceans, evaporates water, and fuels photosynthesis.
Only a small fraction of insolation is needed to power global atmospheric circulation, which distributes heat and carries particles.
The atmospheric circulation is energized by the continuous heating of the tropics, creating Hadley cells and trade winds.
The outflow of cold polar air creates a weaker circulation known as the Ferrell cell.
Earth's rotation deflects winds into prevailing westerlies, causing precipitation on America and Europe's western coasts.
Intensive summer heating generates cyclonic flows, including thunderstorms and hurricanes.
The Impact of Hurricanes, Cyclones, and Tornadoes on Structures
Hurricanes or cyclones frequently make landfall along the northern Gulf of Mexico, Florida, and the East Coast, while typhoons affect parts of Southeast Asia, coastal China, the Korean peninsula, and Japan.
Hurricanes and cyclones can have speeds up to 90 m/s and strike vertical surfaces with power densities of up to 1 MW/m², requiring structures made of modern steel and concrete to withstand the force.
Tornadoes are more restricted, with an average path width of 125 m and length of less than 10 km, but can generate winds in excess of 100 m/s and strike surfaces with more power than hurricanes.
Water's unique properties, such as high specific heat capacity and heat of vaporization, make it the world's most massive temperature regulator and allow for long-distance movement of latent heat in water vapor.
Evaporation and transpiration draw water from soils and vegetation, but the ocean dominates the Earth's energy balance due to its extent and low albedo.
The ocean's poor conductivity leads to strong thermal stratification, with sunlight penetrating only a thin layer of its average depth of 3.8 km. Wind-generated waves mix the water within a thin layer.
Water's Unique Properties
The surface temperature of the shallow mixed layer fluctuates daily and seasonally, reaching more than 25°C in the tropics.
In the Pacific Ocean, trade winds off South America create cool surface water temperatures and nutrient-rich upwelling, supporting abundant marine life.
When trade winds weaken, the warm surface waters extend along the equator, causing El Niño with heavy rains in Peru and drought in Australia and Indonesia.
La Niña occurs when strong trade winds create a larger pool of cool water off the South American coast.
Below the thermocline, water is uniformly dark and close to 4°C, its highest density.
Deep ocean cold waters are brought to the surface in upwelling zones.
The planetary water cycle moves nearly 580,000 km³ annually, with an average precipitation of 3 mm per day.
Thunderstorms release fifty- to one hundred-fold more heat than kinetic energy, while Asia's summer monsoons release five hundred times more latent heat.
Continental precipitation is mostly evaporated or returned to the ocean by streams.
The Earth's Energy Sources: Gravitational and Geothermal
The average continental elevation of 850 m gives the stream flow a potential gravitational energy of about 400 EJ (13 TW) annually, which is an order of magnitude higher than the world's total electricity use.
The exploitation of this energy is limited by the availability of suitable sites for hydroelectricity generating stations, competing needs for water, and the need for minimum stream flows.
The Earth's internal heat, generated by the slow cooling of the core and radioactive decay, constantly reshapes the ocean floor and continents.
The geothermal energy generated by the Earth's internal heat amounts to around 44 TW globally, with a mean flow of less than 90 mW/m².
There is considerable spatial variation in geothermal flux, with higher rates for the ocean floor and even higher rates at hydrothermal vents.
Approximately sixty percent of the Earth's heat is converted into the formation of new sea floor along ocean ridges.
The Role of Basaltic Magma in Plate Tectonics
Basaltic magma rising from the mantle along ridges creates new ocean floor at a rate of less than 5 cm/year.
Rifting process visible in Afar region, East African Rift Valley, and central Iceland.
Oceanic plates eventually collide with continental plates, leading to subduction and recycling of ocean floor into the mantle.
Deep ocean trenches are prominent features of plate subduction.
Violent earthquakes and volcanic eruptions are concentrated along subduction fronts.
Collision between oceanic and continental plates forms mountain ridges.
Magma upwelling and plate subduction drive Earth's geotectonic process.
New ocean floor is higher than the abyssal plain, providing push-power away from the ridges.
Sinking of cold ocean floor along trenches produces pull-power.
Plate movement speed correlates with length of subduction zones.
Earthquakes and volcanic eruptions serve as reminders of energy flow from the Earth's mantle.
Earthquakes and Tsunamis: Key Information
All but 5% of earthquakes occur in subduction or collision zones, mostly in the Pacific coastal areas known as the "Ring of Fire".
The energy released by earthquakes annually is only 1-2% of the total geothermal flux, but larger earthquakes can be highly destructive.
Earthquakes have claimed more lives in the 20th century than volcanic eruptions, cyclones, and floods combined.
Charles Richter introduced the Richter scale in 1935 to measure earthquake magnitude, based on trace amplitude recorded 100 km from the epicenter.
The largest earthquakes with a Richter magnitude of 9.0 release around 1.5 EJ of energy in less than 30 seconds.
Casualties from earthquakes are mainly determined by residential density and housing construction quality.
The 1906 San Francisco earthquake was more powerful than the 1923 Tokyo quake, but Tokyo had a much higher death toll due to densely packed wooden houses.
The deadliest earthquake in recent history occurred in Tangshan in 1976, with an official death toll of 242,219 people.
Some underwater earthquakes generate tsunami, which can travel in deep ocean at high speeds and cause massive destruction when they hit shallow coastal waters.
The Pacific Ocean has the highest frequency of tsunami, with Japan experiencing the most casualties.
The 1896 tsunami in Honshū had waves up to 30 meters high and killed 27,000 people.
Notes on Tsunamis and Volcanic Eruptions
The March 2011 earthquake in Japan had a magnitude of 9.0 and caused a large tsunami, resulting in nearly 16,000 deaths and over 2,500 missing people.
The deadliest tsunami occurred in Aceh province, Sumatra, on December 26, 2004, following a 9.0 magnitude undersea earthquake. It claimed more than 200,000 lives across several countries.
A volcanic eruption in 1883 at Krakatoa in the Sunda Strait destroyed Rakata Island and caused an estimated 36,000 casualties due to the subsequent tsunami.
Volcanic eruptions contribute to a small portion (around 2%) of the global release of geothermal energy.
Heat is the primary component of volcanic energy release, with different carriers such as ash clouds, slow-moving lavas, and pyroclastic flows.
Pyroclastic flows, consisting of volcanic material and extremely hot gases, can reach speeds above 100 km/h and cause significant destruction.
Notable volcanic eruptions include Mount Pinatubo (1991), Mount St. Helens (1980), and Krakatoa (1883).
Volcanoes and Photosynthesis
Tambora eruption vs Yellowstone eruption: Tambora's energy was pitiful compared to the Yellowstone eruption that released 2,500 km³ of ash 2.2 million years ago.
Eruptions over 5 million years: Eruptions over five million years between 65 and 60 million years ago piled up about one million cubic kilometers of basalt lava, forming the Deccan Traps in west central India.
Volcanoes and tectonic plates: Volcanoes are mostly associated with tectonic plate margins, but powerful hot magma plumes have created hot spots far from any subduction or collision zones.
Hawaiian Islands and hot spot: The chain of Hawaiian Islands is being created by a massive hot spot and continues to erupt, with Kilauea volcano being currently active.
Africa's volcanic chain: Africa's plate has a major hot spot that pierces the continent's center, creating the Virunga volcano chain.
Photosynthesis process: Photosynthesis is energized by the absorption of light by pigments in chloroplasts, producing new phytomass. The process is more complex than the commonly simplified equation.
Melvin Calvin's discovery: In 1948, Melvin Calvin and his co-workers revealed the sequential steps of photosynthesis, for which he received the 1961 Nobel Prize for Chemistry.
Chlorophyll absorption maxima: Chlorophylls a and b, the dominant plant pigments, have narrow absorption maxima between 420-450 nm and 630-690 nm.
Photosynthesis and its Mechanisms
Photosynthesis is primarily energized by blue and red light, resulting in the dominance of green and yellow colors in leaves during spring and summer.
Photosynthetically active radiation (PAR) accounts for only about 43% of insolation.
Pigments absorb energy and drive electron transport, generating NADP and ATP.
Carbon is incorporated into carbohydrates through the reductive pentose phosphate (RPP) or Calvin-Benson cycle.
Ribulose 1,5-bisphosphate oxygenase (Rubisco) catalyzes the addition of CO₂ to RuBP, producing PGA.
NADPH and ATP produce triose phosphate, which can form carbohydrates or fatty acids and amino acids.
Rubisco also acts as an oxygenase, leading to photorespiration and the release of CO₂.
Photorespiration reduces the efficiency of photosynthetic conversion in C3 plants.
Widely cultivated crops have low energy conversion efficiencies and require significant water.
There is another photosynthetic path involving hydration of CO₂ to bicarbonate.
Photosynthetic Paths and Energy Usage in Plants
In the C3 photosynthetic pathway, carbon dioxide (CO2) is fixed by the enzyme Rubisco in the mesophyll cells of leaves.
C4 plants have an additional pathway involving the enzyme phosphoenolpyruvate carboxylase (PEP) and bundle sheath cells to increase efficiency.
C4 plants have advantages such as no light saturation, higher temperatures for optimal photosynthesis, and lower water transpiration rates.
CAM plants use crassulacean acid metabolism to absorb CO2 at night and convert it into malate for photosynthesis during the day.
Regardless of the pathway, plants use energy obtained through respiration to support basic functions, nutrient uptake, and defense against insects.
Photosynthesis and Net Primary Production (NPP)
Tissues inaccessible behind thick barks, waxy leaves, or thorns
Respiration claims less than a fifth of new photosynthate in crops, but all of it in mature trees
Maximum theoretical net efficiency of photosynthesis is about four percent
Intensively tended crops have an average of two percent efficiency, while temperate and tropical forests have 1.5 percent
Global continental average for photosynthesis is 0.33 percent and for the entire biosphere is less than 0.2 percent
Annual net primary production is about 120 billion tonnes on continents and 110 billion tonnes in the ocean
Major biomes are limited by temperature and precipitation, not insolation
Tropical rainforests need at least one meter of rain and an average annual temperature above 20°C
Rates of NPP range widely for major ecosystems: 1-3.5 kg/m² in tropical rainforests, 0.5-2.5 kg/m² in temperate forests, and 0.2-1.5 kg/m² for most grasslands
Tropical rainforests harbor more than 600 different species per hectare, but most phytomass is stored in a small number of large trees
Temperate and boreal forests are dominated by a few species, but can store more wood per hectare than tropical forests (up to 3,500t)
Energy Conversion Rates and Metabolism in Nature
Woods with higher lignin and extractives content have higher heating values.
Energy range in North American species is from 17.8 MJ/kg for sweetgum to 21 MJ/kg for Douglas fir.
NPP rates are equal to annual yields for undamaged crops, highest for C crops and optimal conditions.
Iowa farmers harvest over 12t/ha of corn, while wheat harvests in England or Netherlands are around eight.
Rice in Japan and China's coastal provinces produce just over six tons.
Leguminous crops yield mostly less than two, but many vegetables can produce over fifty.
Harvested stalks of sugarcane contain about 25% dry matter.
Well-managed forests have annual increments of 1-2 t/ha of dry matter, but fast-growing tree plantations can produce more.
Heterotrophs metabolize complex organic compounds anaerobically and aerobically.
Anaerobic fermenters include lactic fermentation bacteria and yeasts.
Yeasts produce alcohol without oxygen and carbon dioxide with oxygen.
Some bacterial phyla are aerobic, including nitrogen-fixing bacteria that provide leguminous species with ammonia.
All species in the Animalia kingdom are aerobic heterotrophs.
Heterotrophic Metabolism and Basal Metabolic Rate
The first task of heterotrophic metabolism is to break down carbohydrates into monosaccharides (glucose and fructose), lipids into glycerol and fatty acids, and proteins into amino acids.
ATP conserves the energy released by nutrient degradation, providing energy for new biomass synthesis and locomotion.
Fermentation results in lactic acid or ethanol and CO₂, while aerobic metabolism produces ATP, CO₂, and water.
Anaerobic fermentation has an efficiency of around 30%, while aerobic metabolism's efficiency is about 60%.
Every heterotroph has a basal metabolic rate (BMR), which is the minimum power needed for vital organs.
BMR is measured at rest in a temperature-regulated setting, determined by body weight raised to the power of 0.74 (or 0.75 according to Max Kleiber).
BMR is used to measure basal metabolic rates of mammals, birds, ectotherms, and microorganisms.
Carnivorous mammals have a higher exponent (closer to 0.9), indicating a greater BMR and increased increase with body mass.
Desert rodents have a lower exponent (just below 0.5) to minimize energy needs in a hostile environment.
Basal Metabolic Rate and Energy Expenditure in Endotherms and Ectotherms
Endotherms, such as mammals and birds, have a core body temperature that remains constant and high, and therefore have a much higher basal metabolic rate (BMR) compared to similarly-sized ectotherms.
Larger endotherms, like albatrosses, have a higher BMR than smaller ones.
Specific BMR declines exponentially with larger body mass.
The low specific BMR of large mammals allows them to go without eating for days and hibernate when at rest.
Animals lighter than shrews and hummingbirds have limited mass due to high rates of heat loss.
The total daily metabolism is about 2.5 times BMR for rodents and more than four times BMR for birds.
The metabolic scope of heterotrophs determines their running, flying, and swimming abilities.
Mammals have an average scope of ten, birds around fifteen, and reptiles and amphibians less than five.
Songbirds have a high metabolic scope and can develop up to 150 mW/g, while small rodents and iguanas have lower scopes.
Canids have the highest known metabolic scope, surpassing thirty.
Running, swimming, and flying: The endurance and energy costs of animal locomotion
Cheetahs, despite being the fastest animals, can only sustain a short distance of less than 100 meters while hunting.
Wolves can chase their prey without stopping for up to 20 minutes, covering over 30 kilometers daily.
Larger animals have more power available for running and can take advantage of elastic recoil in their long leg muscles to reduce energy needs.
Massive animals like bison, grizzly bears, and hippos may not appear to be sprinters, but they can still outrun humans.
Asian elephants can reach speeds of about 25 km/h, but if humans can run 100 meters in under 14 seconds, they can escape.
Swimming requires less energy than running and flying, with running being more energy-demanding than flying for smaller body weights.
Large birds have difficulty getting airborne due to the power needed for flight rising more quickly than what their muscles can deliver.
Long-distance migrations are easier when animals can feed along the way.
Songbirds migrating in cool weather may expend more energy during stopovers than during flight.
The most impressive long-distance migration is the non-stop flight of tiny songbirds over vast oceans, relying on stored fat as fuel.
Energy Flows and Trophic Levels in Ecosystems
The maximum distance a small songbird can fly non-stop is limited by the amount of fat it can store before the trip.
Thermodynamic imperatives govern energy flows in ecosystems.
Autotrophs, despite relatively inefficient photosynthesis, dominate the energy cascade and biomass.
Herbivores, such as rodents and ungulates, are more abundant than carnivores or tertiary consumers.
Omnivory is common, as species can move up or down trophic levels based on resource availability.
Decomposers break down organic matter, providing nutrients to autotrophs and heterotrophs.
Terrestrial ecosystems have short feeding cascades, while tropical rainforests can support up to five trophic levels.
The Complexity of Marine and Terrestrial Food Webs
Snakes feed on frogs, and birds feed on snakes.
Marine ecosystems are based on primary production by phytoplankton.
Marine food webs are generally more complex than terrestrial food webs.
In marine ecosystems, the total standing heterotrophic biomass is larger than the mass of photosynthesizing phytoplankton.
Oceanic autotrophs are mostly species of microscopic phytoplankton.
Higher trophic levels in marine ecosystems include primary consumers, secondary consumers, tertiary consumers, and quaternary consumers.
The largest marine mammals and fish are filter feeders.
The declining numbers of heterotrophs in higher trophic levels are associated with increasing body size.
Megaherbivores, such as elephants and giraffes, have the largest body mass in modern ecosystems.
Generalizations regarding transfers within the trophic pyramid have been difficult to make.
Energy Efficiency in Ecosystems
Raymond Lindeman's pioneering studies on aquatic life in Lake Mendota showed that autotrophs have an efficiency of 0.4%, primary consumers retain less than 9%, secondary consumers about 5%, and tertiary feeders about 13% of available energy.
These approximations were mistakenly generalized into the "ten percent law of energy transfer", which subsequent studies proved to be incorrect.
Bacteria and herbivores can be more efficient converters than carnivores.
Final energy transfers in ecosystems depend on exploitation, assimilation, and production efficiencies.
The abundance of herbivores is limited by predation, while carnivores are limited by prey availability.
Assimilation efficiencies depend on feed quality.
Production efficiency is higher among ectotherms and varies based on trophic level.
The share of energy converted to new biomass at the next trophic level varies across species without clear correlations.
Evolutionary Success, Trophic Efficiency, and Energy in Human History
Trophic efficiency does not determine evolutionary success, as both low-efficiency endotherms and high-efficiency ectotherms thrive similarly in similar environments.
In complex food webs, reducing the abundance of a single species can have unexpected consequences.
Sea urchins caused massive damage to kelp forests in the Pacific Northwest, impacting species dependent on these marine plants, due to the decline in sea otter population caused by orcas' predation.
Humans, as foragers, relied on somatic energy and reasoning, using fire, stone tools, clubs, bows and arrows, and bone tools.
The domestication of large animals, starting with cattle, provided humans with increased capacity for work.