Detailed Notes on the History of Life on Earth

The History of Life on Earth

1.3 Studying Earth’s History

• Microevolution:

  • Can be observed in hours or days in a laboratory.

• Macroevolution:

  • Takes much longer spans of time.

  • Examples:

    • Appearance of new species.

    • Evolutionary branching of lineages of species.

    • The appearance of new traits.

  • Must be studied across deep time.

    • Thousands, millions, and billions of years of history.

  • Requires a solid understanding of geology.

1.4 Geology

• The history of the Earth is recorded in its rocks.

• Three kinds of rocks:

  • Igneous: Formed from magma/lava.

  • Metamorphic: Igneous rock modified under extreme pressure and high temperature.

  • Sedimentary: Igneous and metamorphic rock that erodes and is deposited, reforming into rock in the presence of water.

• Relative Dating:

  • We can determine the ages of rocks relative to each other.

  • Sedimentary rocks are deposited with the oldest on the bottom.

  • Each new layer of deposition is a stratum (pl. strata).

  • Fossils are typically contained in sedimentary rock deposits.

  • The age of the fossil is relative to the stratum in which it is found.

1.5 Fossils

• Fossils are the preserved remains of ancient organisms.

• Inform us about the organism’s morphology.

  • Morphology: the study of body forms.

• Tell us when and for how long a species roamed the Earth.

• Provide a direct record of evolution.

• Fossils are rare – species must die under the proper conditions to be fossilized.

1.6 Relative Dating

• Stratigraphy - Fossils can be dated relative to the stratum of rock in which they were deposited

• Fossils of similar organisms are found in widely separated places on Earth

• Certain fossils are always found in younger strata, while other fossils are always found in older strata

• The organisms found in younger strata are more similar to modern organisms

1.7 Absolute Dating

• Unstable radioactive isotopes (radioisotopes) decay into stable isotopes

• Isotope decay occurs at a precise, universal rate

• Half of a sample of Carbon-14 will decay into Nitrogen-14 in 5,700 years

• A 5,700 year old sample will contain 50% Carbon and 50% Nitrogen

• This period of time is called the Half-Life of an isotope

1.8 Absolute Dating – Warning!

• Carbon-14 dating is ONLY used for samples 100 to 60,000 years old

• Potassium-40 is ONLY used for samples 10 million to 4.5 billion years old

• Uranium-235 is ONLY used for samples 200,000 – 4.5 billion years old

• There are several other less common isotopes used in combination to date samples between 50,000 and 10 million years old

1.9 Dating Geologic Events

• Dating events in geological time requires BOTH relative and absolute dating methods

• Sedimentary rocks and depositional layers must use relative dating

• Igneous rocks can use absolute dating

• To apply absolute dates to sediments, scientists must find places where igneous and sedimentary rock were formed at the same time

• Paleomagnetic dating

  • Uses the orientation of iron filings in rocks

  • Orientations changed based on the direction of the Earth’s magnetic field

  • Can be used on sedimentary and igneous rocks

1.10 Earth History

• The history of the Earth is divided into spans of time

  • Eon > Era > Period > Epoch > Millennium > Century > Decade > Year

• Divisions were based on dramatic, global changes

  • In the fossil record, indicating mass extinctions or species shifts

  • In the geological record, indicating mass movements of the Earth’s crust and the continents

• These time divisions have been modified over the years as we learn more

• Haven’t changed recently

1.12 A Dynamic Earth

• For most of our history, we believed Earth was stagnant and unchanging

  • Had poor/no explanation for geological formations

  • Earth was “created” in its present form

• 1912 – Alfred Wegener (“Vagner”)

  • Proposed Continental Drift

  • Seemed impossible – no mechanism could allow continents to move

  • Wegener dies in a North Pole expedition gathering data

  • Completely unsupported until the 1940’s – submarine mapping during WWII

• 1960’s – Science of Plate Tectonics and Continental Drift Theory earns merit and acceptance among scientific community

1.13 Continental Drift & Plate Tectonics

• Convection Zone – Hot mantle rises, forces apart ocean floor

• Ridge Zone – Area where expansion is occurring

• Subduction Zone – Old crust is sucked back down and melts

• Uplift Zone – Extra material is forced up; volcanoes and earthquakes are common

1.14 Continental Movements

• Great video, but be aware, he uses some “colorful” language that some may consider inappropriate

• Video Available at: https://youtu.be/9vvm1fJkA6M

1.15 Volcanism and Bombardment

• Massive volcanic eruptions have occasionally shaped Earth’s climate and affected life

• Meteor impacts have also had dramatic effects on Earth’s climate and biota

• The Era of Heavy Bombardment during the Hadean Eon

1.16 Earth’s Changing Climate

• The movement of the continents, volcanism, impacts from space, and life on Earth have all caused dramatic changes in Earth’s global climate

  • Sea Level

  • Temperature

  • Humidity/Precipitation

  • Atmospheric Oxygen (O2) concentration

  • Atmospheric Carbon Dioxide (CO2) and Nitrogen (N2) are also important

1.17 Sea Level

• Sea level changes throughout Earth's history are shown graphically.

• Asterisks indicate mass extinction events.

• The graph spans from the Proterozoic Eon to the Quaternary Period.

• The x-axis represents millions of years ago, ranging from 500 to the present.

• Key periods include Cambrian, Ordovician, Silurian, Devonian, Carboniferous, Permian, Triassic, Jurassic, Cretaceous, Tertiary, and Quaternary.

• The graph shows high and low sea levels, with notable drops coinciding with mass extinction events.

1.18 Atmospheric Oxygen Concentration

• The graph illustrates changes in atmospheric oxygen (O2) concentration over millions of years

• Key events are marked:

  • First Life at 4,000 million years ago

  • First Bacteria at 3,500 million years ago

  • First Photosynthetic Bacteria at 2,700 million years ago

  • First Aerobic Bacteria at 2,300 million years ago

  • First Eukaryotes at 1,800 million years ago

  • First Multicellular Eukaryotes at 1,000 million years ago

  • First Chordates at 540 million years ago

  • Invasion of Land at 480 million years ago

  • Giant Flying Insects at 320 million years ago

  • First Flowering Plants at 130 million years ago

• The concentration of O2 in the atmosphere is shown in percentage, ranging from 0% to 35%.

• The graph shows a gradual increase in O2 concentration over time, with significant spikes and plateaus.

1.19 Global Temperature

• Past global temperature fluctuations are represented from the Precambrian period to the present day (Pleistocene epoch).

• Temperatures are expressed as warm or cool, with approximate average global temperatures indicated (e.g., 22°C, 17°C, 12°C).

• The graph includes major geologic periods such as Cambrian, Ordovician, Silurian, Devonian, Carboniferous, Permian, Triassic, Jurassic, Cretaceous, Tertiary, and Pleistocene.

• Alternating periods of warm and cool climates are evident.

1.20 Atmospheric CO2 & Temperature

• Graph representing atmospheric CO2 levels and corresponding temperature changes over millions of years.

• The x-axis spans from the Precambrian era to the present day (TODAY), marking significant geological periods along the way.

• CO2 levels are not explicitly quantified but are correlated with temperature anomalies (ΔT in °C).

• Temperature anomalies are indicated at various points:

  • Δ=10°C during the Precambrian.

  • Δ=6°C during the Paleozoic.

  • Δ=3°C during the Mesozoic.

• The graph covers major eras: Precambrian, Paleozoic, Mesozoic, and Cenozoic, with more detailed epochs within the Tertiary period.

1.21 Addressing Modern Climate Change

• Earth’s climate has changed dramatically over its 4.6 billion-year history.

• Historical changes in temperature, sea level, and Carbon Dioxide have taken hundreds of thousands of years.

• Often times, these changes were indicative of other events, such as heavy volcanic activity or meteor bombardment.

• These changes, when more sudden, were precursors to major extinction events.

• Modern climate change IS at least partially man-made.

• Dramatic increase in CO2 emissions in less than 200 years

• Coincides perfectly with the discovery and use of Fossil Fuels

• Fossil Fuels were formed by plant matter during the Carboniferous Period

• This is not debated among scientists and ecologists*

• *Unless you count scientists who are employed or funded by corporations

1.22 Quaternary Period CO2 & Temperature Change

• Graph displays carbon dioxide (CO2) levels and temperature changes during the Quaternary Period.

• The X axis represents thousands of years before the present, ranging from 400,000 years ago to the present.

• CO2 levels are shown in parts per million by volume (ppmv), ranging from 180 to 300 ppmv.

• Temperature changes are indicated in degrees Celsius (°C), ranging from -10 to 2.

• The graph illustrates a correlation between CO2 levels and temperature changes, with higher CO2 levels generally corresponding to warmer temperatures.

• Data shows cyclical patterns, with peaks and valleys in both CO2 levels and temperature aligned over time.

1.23 Study Handout Reminder

• Students are expected to know Eons, Eras, Periods, Epochs, Age of onset, and important events

• This page is available as a full-page in CANVAS with added instructor’s notes

• Use handout from CANVAS to study:

  • Learn “rounded” dates

  • Pay attention to events and notes added by instructor

1.24 Major Events in Earth History

• Big Bang $\approx$ 14 billion years ago

• Our Sun begins fusing, planets (including Earth) form $\approx$ 4.6bya (Hadean Eon)

• First life (Prokaryotes) appear $\approx$ 3.5bya (Archaean Eon)

• Cyanobacteria begin photosynthesizing $\approx$ 2.7bya (Archaean/Proterozoic Eon)

• First Eukaryotes appear $\approx$ 1.8bya (Proterozoic Eon)

• Multicellular organisms $\approx$ 1.0bya (Proterozoic Eon)

• Snowball Earth Catastrophe $\approx$ 650mya (Proterozoic Eon)

• First Animals appear $\approx$ 630mya (Ediacaran Period)

• Cambrian Explosion $\approx$ 550mya (Paleozoic Era)

• Age of Reptiles $\approx$ 250-65mya (Mesozoic Era)

• Age of Mammals $\approx$ 65mya to present (Cenozoic Era)

• Ice Age Glaciations $\approx$ 2.6mya (Pleistocene Epoch)

• First human ancestors $\approx$ 2.1mya (Pleistocene Epoch)

• The Age of Humans $\approx$ 100,000 years ago to present (Anthropocene/Holocene Epoch)

1.25 Big Bang - 14 Billion Years Ago

• The first subatomic particles to be formed included protons, neutrons, and electrons

• Though simple atomic nuclei formed within the first three minutes after the Big Bang, thousands of years passed before the first electrically neutral atoms formed

• The majority of atoms produced by the Big Bang were hydrogen, along with helium and traces of lithium

• Giant clouds of these primordial elements later coalesced through gravity to form stars and galaxies, and the heavier elements were synthesized either within stars or during supernovae

1.26 Solar System Forms - 4.6bya (Hadean Eon)

• The early Earth was molten and unable to support life

• Radioactivity kept the Earth hot for about 1 billion years after formation

1.27 First Life (Prokaryotes) Appears - 3.5bya (Archaean Eon)

• Earth took about 1 billion years to cool and solidify while granite crust developed

• Water vapor began to condense to form oceans

• As soon as Earth was cool enough, simple Prokaryotic cells appeared

  • Domain Bacteria

  • Domain Archaea

• Although there are several strong hypotheses explaining the origins of life, we do not know for certain how life began on Earth

• We do know that all life since then descends from a common ancestor

  • Cellular, contained nucleic acids, proteins, lipids, and carbohydrates

1.28 Bacterial Photosynthesis - 2.7bya (Archaean Eon)

• The Great Oxygen Event/Catastrophe occurred when unicellular Cyanobacteria began a primitive form of photosynthesis

• Photosynthesis produces O2 as a “waste” gas

• Our previously anoxic atmosphere began to accumulate gaseous Oxygen, which was toxic to most life

• Caused a mass extinction of anaerobic species

1.29 First Eukaryotes Appear - 1.8bya (Proterozoic Eon)

• Eukaryotes (Domain Eukarya) evolved from Prokaryotes

• Eukaryotes developed

  • To be larger

  • Complex cytoskeletons

  • The ability to shift/flex their form

  • Endocytosis/Exocytosis

  • True membranous organelles

  • A true nucleus

• Endosymbiosis provided for the formation of Mitochondria and Chloroplasts

1.30 Multicellular Organisms 1.0bya (Proterozoic Eon)

• Eukaryotes had a complex external structure that allowed for the formation of colonies

• Colonies displayed cell specialization which increased efficiency

• Began to form primitive tissues, organs, and organ systems

• Gave rise to multicellular organisms

1.31 Snowball Earth Catastrophe 650mya (Proterozoic Eon)

• Due to continental shifts and massive volcanism, Earth entered a sudden global ice age

• The equator would have been as frozen as Antarctica

• Most life on Earth died

• What survived was severely impacted by the climate

• Scientists hypothesize that this sudden extinction selected for the strongest, most adaptive organisms

• Once earth began to thaw, a massive adaptive radiation of these very “fit” species began

• This is called the Ediacaran period, which led to the Cambrian explosion

1.32 First Animals Appear 630mya (Ediacaran Period)

• The Ediacaran period is known as the first time where true, primitive animals were present on Earth

• Almost none would be familiar to us today

  • Basic sponges, jellyfish, and corals

• Predominantly filter-feeders

• Consumed algae

• All life was restricted to the oceans

1.33 The Cambrian Explosion 550mya (Paleozoic Era)

• Animals with which we are more familiar get their start in the Cambrian Period in a sudden adaptive radiation of new species

• Predator/prey interactions replaced filter-feeding

• The oceans became a dangerous place

• Pushed natural selection and adaptation to occur quickly

1.34 The Colonization of Land 480mya (Ordovician Period)

• During the Ordovician, primitive plants, fungi, and animals moved onto land to escape the predation pressure of the ocean

• Animals, such as horseshoe crabs were still tied to the ocean

• No animals were capable of surviving for long on land

• Plants and fungi worked together to terraform the terrain into more suitable habitat

1.35 The Age of Fishes 420mya (Devonian Period)

• The ocean is filled with sharks, skates, rays, and a new group of ray-finned fish

• Also present are predatory Mollusks such as Octopi and Squid

• Again, in an attempt to escape predation, some fish (tetrapods) began to pull themselves onto land

• The fossil Tiktaalik is one sample of an intermediate organism

• Remained tied to the ocean, but could spend time on land

1.36 The Age of Amphibians 350mya (Carboniferous Period)

• Still not completely free of the aquatic lifestyle, tetrapodal amphibians became common on land

• Giant insects also present

• A climactic shift caused fungi to become less prevalent on land

• Fungi function as decomposers

• Loss of fungi led to lack of decomposition

• Ferns and plant matter was unable to be broken down

• Burial of plant material led to the formation of fossil fuels

1.37 Age of Reptiles 250-65mya (Mesozoic Era)

• The Permian extinction led to the rise of the Age of Reptiles

• The Triassic, Jurassic, and Cretaceous periods

• Dinosaurs, as well as other reptilian creatures ruled the earth

  • Turtles, snakes, crocodiles, lizards

  • Pteranadons, Icthyosaurs, Plesiosaurs

• Cone-bearing Gymnosperms are dominant plant

• Flowering plants evolve late in the Cretaceous

• Toward the end of the Cretaceous, dinosaurs are failing

• Meteor impact ends the age of the dinosaurs in an event called the KT Extinction

1.38 Age of Mammals 65mya to Present (Cenozoic Era)

• Following the KT Extinction, mammals are able to capitalize upon the resources no longer being used by dinosaurs

• Leads to an adaptive radiation of mammals and birds

• Although mammals, most would be unfamiliar to us

• The rise of flowering plants leads to pollinators such as honeybees and hummingbirds

1.39 Ice Age Glaciations 2.6mya (Pleistocene Epoch)

• The Ice Age occurred during the Pleistocene

• Many well-known but extinct mammals

  • Wooly mammoth, sabretooth tiger

• Glaciers pushed down through Pennsylvania

1.40 First Human Ancestors 2.1mya (Pleistocene Epoch)

• The ancestors of humans evolve in central African continent

  • Ardipithecus species

  • Australopithecus species

• Display ability to use tools

• Critical thinking skills

• Development of communication

• Beginning development of culture

• Genus Homo evolves and pushes out of Africa across globe

1.41 The Age of Humans 100,000 Years Ago

• The Anthropocene/Holocene Epoch

• Human ancestors continue to invent, globalize, and develop

• As hominids become more advanced, cranial capacity increases, and jaw size and musculature decrease

• Correlates with use of tools and fire

• Homo species go extinct at different times, except of course Homo sapiens