Astrobiology (Geo 080) Study Guide — Spring 2022 — Exam 1

What role did the Allan Hills meteorite play in establishing the Astrobiology Program at NASA?

1984 discovered in Allan Hills, Antarctica. The Mars meteorite and the excitement surrounding it gave a jumpstart to NASA's renewed search for life beyond Earth.

Which planets in our solar system have liquid water at the surface today? Which of them have signs of life (past or present)?

Earth is the only known planet (or moon) to have consistent, stable bodies of liquid water on its surface.

How has our sun's brightness changed over time? What components in our atmosphere have offset the effects of a less bright sun toward maintaining liquid water at our surface over most of Earth history?

Our sun's brightness has increased over time warming our planet . Initially we had more greenhouse gases enabling us to retain a good surface temperature. Now there are fewer greenhouse gases in the atmosphere

How did our moon form?

It proposes that the Moon formed during a collision between the Earth and another small planet, about the size of Mars. The debris from this impact collected in an orbit around Earth to form the Moon.

What is the habitable zone and what defines its width and distance from the star?

It is the area around a star where liquid water could exist on a

planet, given it has sufficient atmosphere. The habitable zone is defined by how bright a star is and how far from a star the planet lies with a right atmospheric composition. Whether a planet is in the HZ is dependent on its host star and its

orbital period

What is the earliest evidence for liquid water on Earth? Why is liquid

water important in astrobiology studies?

4 billion years ago, liquid water is so important in astrobiology studies as it equates to habitability, therefore the conditions suitable for life.

What was the Late Heavy Bombardment? What is the evidence for or

against it? (Hint: how does the moon help us understand Earth's early

impact history?)

The Late Heavy Bombardment (LHB) is a theory that the Earth suffered through an intense spike in asteroid bombardment roughly 4 billion years ago. The moon's crater record and the hundreds of kilograms of lunar material returned to Earth by the Apollo astronauts.

What are some of the "impacts of impacts?"

Some theorize that the impacts may have helped deliver life on earth. If life originated in environments on the Earth's surface, it only could have happened after the bombardment stopped. but also may have delayed life on earth for a while.

What are the earliest possible records of life on Earth—that is, the types of evidence and their ages?

4.1 billion years old biogenic carbon preserved in zircon.

3.5 billion years old stromatolites (microbial structures)

3.5 billion earliest fossil records of all time

3.0 billion or more first photosynthesis (indicated by the increase of O2 in the atmosphere)

How has oxygen varied in our atmosphere over time?

Oxygen levels are generally thought to have increased dramatically about 2.3 billion years ago. Photosynthesis by ancient bacteria may have produced oxygen before this time. O2 in the atmosphere = life on earth (however O2 does not necessarily equate to life)

What was 'Darwin's dilemma,' and how was it resolved after his death?

Darwin thought evolution was a very slow process, proceeding in tiny changes over many generations, didn't understand how life could have evolved so quickly during the Cambrian era. Excavations around the world have since uncovered fossils that show the change was rapid, but not too rapid to be inconsistent with evolutionary theory. It actually took millions of years.

Compare the relative histories of liquid water on Venus, Earth, and Mars.

Venus may have had a shallow liquid-water ocean and habitable surface temperatures for up to 2 billion years of its early history, however it lost habitability due to its atmosphere.

Mars: thin atmosphere prevents liquid water from forming on the surface, evidence for liquid water in the past.

Compare, in simple terms, the biggest differences between the surface conditions and atmospheric compositions for Venus, Earth, and Mars.

Mars: thin atmosphere, cold temperatures, target of meteorites and huge storms : 95% CO2, 3%N2, 1.5 Argon

Venus:.clouds of sulfuric gases, It has a crushing carbon dioxide atmosphere 90 times as thick as Earth's. Temperatures reach 864 degrees Fahrenheit :96% CO2, 3%N2, 1% other

Earth: Temperate, allows liquid water on the surface with stable hydrogen compound (72% Nitrogen, 21%O2, 1% Argon)

What is the evidence for past liquid water on Mars?

Geologic evidence,

What are Enceladus and Europa and why are they exciting targets in

astrobiological research? Where and why do they have liquid water?

Enceladus, an ocean-harboring moon of Saturn, possible habitability, comparing Earth's deep-sea plumes, where microbial life thrives, with the ones found on the icy moon and suggesting that they may be home to Earth-like microorganisms.

Europa is one of four moons orbiting Jupiter. From fluctuations in Europa's magnetic field that suggests a conductor of some sort, scientists also think there is an ocean deep beneath the surface of the moon. This ocean could contain some form of life.

What are exoplanets and how do they factor into the Drake Equation?

Exoplanets are planets beyond our solar system. The Drake equation is a probabilistic argument used to estimate the number of active, communicative extraterrestrial civilizations in the Milky Way Galaxy. As we haven't discovered the majority of exoplanets increases the odds of finding those civilizations.

Roughly how many exoplanets have been discovered?

5011

What is the transit method for exoplanet discovery? How does it work, and what can it tell us about an exoplanet?

Transiting exoplanets is the method of finding exoplanets using a telescope. When light passes through atmospheres we can identify the gases present in it, thus finding planets. (relies heavily on timing and chance)

How might life be detected on an exoplanet?

Life on an exoplanet might be detected by the gases in the atmosphere that may give a biosignature.

How long have ideas regarding the existence of life throughout the

universe have

been around? Who were some early thinkers on this topic?

Epicurius (300BC) > plurality of worlds

Giodano Bruno (1584) > 7 planets (including the moon) > transition to geocentric from heliocentric

What problem did Giordano Bruno identify, and in what year?

In 1582 he published his ideas : the most notable of these were his theories of the infinite universe and the multiplicity of worlds, in which he rejected the traditional geocentric (burnt at the stake for heresy)0

How are planets orbiting stars other than our sun detected?

If we measure the brightness of stars we can figure out when they are obscured.

Why were giant planets the first to be discovered?

They obscure the most amount of light and therefore are the easiest to spot from earth.

What was the first planet-finding spacecraft capable of finding rocky

planets? When did it launch?

Kepler is the first NASA mission capable of finding Earth-size planets in or near the habitable zone, the region in a planetary system where liquid water can exist on the planet's surface. It launched March 7, 2009.

What is the most important condition for habitability that has driven most research so far?

The presence of liquid surface water is the most important condition for habitability.

What are the three main categories of effects on planetary habitability?

The planetary environment, stellar properties, and the planetary system environment

What are our best prospects for finding life elsewhere in our solar system?

Finding a planet that has similar conditions like earth

Why/how do studies of Earth help guide our search for life elsewhere?

There are basic requirements for life on our planet (that are likely true for other planets):

-Tells us about the chemical properites present in life

-We observe multiple chapters earths in order to have a wider range of templates that may aid us to find life elsewhere

What are the ingredients for life?

1.Chemical building blocks like carbon, oxygen, hydrogen and nitrogen,

2.An energy source (solar or chemical)

3.Situated in the habitable zone

What are two fundamental characteristics of life?

Life spreads and increases exponentially and that life needs energy either solar or chemical

What are the special properties of water that make it necessary for life as we know it?

Water dissolves almost every substance + is an ideal substance for transporting components of a cell (either through the flow or transfusion) +Charge property allows it to react with other species +Organisms have to take in components to survive so they shuttle in components into their membrane and water provides an efficient way to do so

What roles does temperature play in controlling life?

Temperature helps determine what may enter the molecule ( if too high the cell membrane can become more fluid and possibly allowing some potentially harmful molecules to enter)

(if too low , there is a decrease of the overall fluidity of the membrane and decreasing its permeability and potentially restricting entry of important molecules such as oxygen and glucose into the cell)

Why do water molecules have charge (polarity)?

Water (H2O) is polar because of the bent shape of the molecule. The shape means most of the negative charge from the oxygen on side of the molecule and the positive charge of the hydrogen atoms on the other side of the molecule.

What is NASA's definition for life?

Life is a self-sustaining chemical system capable of Darwinian evolution" and considered the specific features of the one life we know —Terran (Earth) life.

What is Darwinian evolution?

Evolution theory that states that all species of organisms arise and develop through the natural selection of small, inherited variations that increase the individual's ability to compete, survive, and reproduce

What is homeostasis?

In biology, homeostasis is the state of steady internal, physical, and chemical conditions maintained by living systems.

Understand what it means to say that life is in disequilibrium with its

surroundings.

Chemical disequilibrium in planetary atmospheres has been proposed as a generalized method for detecting life on exoplanets through remote spectroscopy. Among solar system planets with substantial atmospheres, the modern Earth has the largest thermodynamic chemical disequilibrium due to the presence of life.

What are the three domains of life?

Archaea, Bacteria, and Eukarya

Contrast autotrophy and heterotrophy.

Autotrophs are known as producers because they are able to make their own food from raw materials and energy.

Heterotrophs are known as consumers because they consume producers or other consumers.

Describe the Miller-Urey experiment.

The Miller-Urey experiment refers to the 1952 synthesis of organic compounds (specifically the amino acidà central building blocks for life) from inorganic chemicals (specifically: methane CH4, ammonia NH3, water H20, and hydrogen H2) using an electrical discharge. Amino acids are also found in meteorites (also formed without life). Proteins are made up of amino acids (so building blocks).

Photosynthesis is an example of which?

Photosynthesis is an example of an anabolic process. Anabolic reactions are those metabolic reactions in which complex substances are formed from simpler organic substances.

Does photosynthesis always produce oxygen?

Photosynthetic reactions can occur without oxygen that is anoxygenic; thus, they do not produce oxygen.

Does carbon fixation require light?

In aquatic ecosystems, both freshwater and marine, there is a widespread knowledge that carbon dioxide (CO2) fixation occurs in the dark

What role might minerals have played in the origins of life?

resistant to alteration + when formed the isotopes can capture the properites of their surrounding environments (therefore can tell us many things about life à water in the rocks billions of years ago)

How might deep-sea vents have contributed to the origins of life?

By creating protocells in hot, alkaline seawater. The process may work on a planet that does not have any continents

What is the basic argument behind the RNA-first model for the origins of life?

life on Earth began with a simple RNA molecule that could copy itself. Non-biological pathways to RNA that are extremely difficult to form

What is panspermia?

Theory: Exchange of the building blocks of life to earth /microorganisms or chemical precursors of life present in outer space and able to initiate life on reaching a suitable environment

What is a black smoker?

a particle-filled cloud resulting from metallic-rich solutions gushing form the seafloor into the ocean water, containing many chemicals central to life

What role might wet-dry cycles have played in the origins of life?

Wet-dry cycles allow more complex organic molecules to develop out of simpler organic molecules.

How does pyrite form and why might it be a fingerprint of life?

Pyrite is formed by bacteria that remove oxygen from sulfate in the water, producing sulfide that reacts with iron to form pyrite.

What is metabolism and the difference between anabolic and catabolic?

Metabolism is the chemical reaction in the body's cells that change food into energy. Anabolism is the synthesis of complex molecules from simpler ones. These chemical reactions require energy. Catabolism is the breakdown of complex molecules into simpler ones.

What is sulfate reduction?

Sulfate reduction is a type of anaerobic respiration that utilizes sulfate as a terminal electron acceptor in the electron transport chain.

Is oxygen the only oxidant that can support microbial decomposition of organic matter?

Some decomposition occurs in the absence of oxygen (anaerobic conditions)

What are isotopes, and how might carbon isotopes provide evidence for life?

When photosynthesis occurs C12 is easier to break than C13 the other à during that process

Light carbon isotopes in carbon remains and organic remains are the first signs of life on the planet

What is the evidence for possible early life in Earth's oldest hydrothermal vents? What is a hydrothermal vent?

As we think about actual fossils > hydrothermal vents are evidence for early life (all based on chemosynthesis )

What are stromatolites? How do they form? Are they a potential

signature of ancient life?

Stromatolites are layered accretionary structures formed in shallow water by the trapping, binding, and cementation of sedimentary grains in biofilms (specifically microbial mats).

How old is the oldest possible fossil evidence for life on Earth, and what is that evidence?

3.5 Billion years ago in Western Australia. Made of quartz with possible carbonaceous microfossiles.

The basic differences between prokaryotic and eukaryotic life.

Eukaryotes evolved from prokaryotes around 2.7 billion years ago. The primary distinction between these two types of organisms is that eukaryotic cells have a membrane-bound nucleus and prokaryotic cells do not.

How old is the oldest evidence for eukaryotic life on Earth?

microfossils - 1.5. billion years old

How old, roughly, is the oldest evidence for animal life on Earth?

700 million years ago

What are nutrients?

substances normally obtained in diets that are needed for life and growth. ex. carbon, nitrogen, phosphorus, sulfur, and more

What are nutrients used for?

The substances, normally obtained in the diet, that are essential to the life and growth of an organism

How is fixed nitrogen formed by life and why is this process important?

Certain organisms take N2 from the atmosphere > very few organisms that can take N2 (cyanobacteria can take it in the ocean) à after death other organisms can use their decay products

Understand the difference between photosynthesis and respiration.

The main difference between photosynthesis and respiration is where it occurs, one being in plants and some bacteria and the other being in most every other living thing. The other difference is that plants require sunlight for the process to occur, whereas respiration does not.

How are nutrients released in the deep ocean returned to surface waters?

When wind blows :

* Surface water is moved and the water is pushed out perpendicular to the wind direction

* The water from the deep is ocean is brought up

*This also explains why Californian water is so cold à a lot of wind causing cold deep ocean water to come up

Understand the difference between photosynthesis and respiration.

Photosynthesis consists of two stages light reaction and dark reaction. Respiration consists of two stages, they are inhalation and exhalation.

What role does light in the ocean play in controlling the distribution of nutrients with increasing water depth?

The organisms present on the surface in the light, after death those organisms settle to the depths of the ocean. Through decomposition the nutrients are released in the deep waters.

Is the surface ocean rich or depleted in phosphorus and (fixed) nitrogen relative to the deep ocean and why?

Certain organisms take N2 from the atmosphere à very few organisms that can take N2 (cyanobacteria can take it in the ocean) à after death other organisms can use their decay products. N increases as you go deeper while the inverse is true for P.

What role does plate tectonics play in recycling nutrients?

Plate tectonics plays a critical role in long-term recycling of phosphorus, best way to recycle it is via plate tectonics (when continents collide) as the seafloor can be brought up to mountain ranges where the levels of phosphorus can be returned

Are many elements important to life beyond C, H, N, O, P, and S? What roles might they play?

Micronutrients (small quantities can be found in living organisms but still are extremely important) à availability in the ocean can be related to a myriad of factors

How do greenhouse gases help keep Earth's surface warm?

Greenhouse gases in our atmosphere trap just enough heat from the sun to keep our planet temperate.

Discuss the importance of methane as a greenhouse gas in the very ancient world versus more recent times? Why has this role changed (hint: think about the emergence of oxygen in our atmosphere)?

Originally there was abundant methane in our atmosphere however oxygen became more abundant when biology began to produce methane. These methane clouds forced hydrogen to leave the atmosphere, allowing today's oxygen-rich air to develop.

What is another very important greenhouse gas today and in the past?

CO2 is a very important greenhouse gas today as it is at a surplus and leading to a warmer planet.

Are organic molecules reliable evidence for the earliest oxygen production by life on Earth?

Organic molecules are a reliable indicator for life on Earth.

How does the biological pump work?

Organic matter settles in the deep ocean and is brought back to the surface in the form of nutrients.( satellite detects distribution of chlorophyll life in the oceans à you can see the upwelling in polar regions)

What name is given to the general

species from becoming an advanced

cause that prevents an intelligent

space-faring civilization?

The Great Filter

How does the biological pump work?

light penetrates through the ocean's surface → photosynthesis → produces organic matter that falls and settles into the deep ocean → nutrients are upwelled back to the surface

How is fixed nitrogen formed by life and why is this process important?

short and long term way of allowing nutrients to become available. plants bring nitrogen in the air allowing it to become available for other plants when they're done with it.

What are the factors that can limit the lifetime of an advanced civilization?

External and internal factors, like the climate change on the planet and how the civilization deals with it; an asteroid hitting the planet, and etc.

Why do numbers calculated from the Drake Equation vary so much?

The equation was made for the discussion, the variables can be changed because we have no idea of the accurate variables.

What is the Fermi paradox?

The Fermi Paradox asks why we haven't found signs of alien life yet. "Where is everybody"

What are some possible explanations for the Fermi Paradox?

Extraterrestrial life is extremely rare.

● Intelligent life is rare.

● Civilizations destroy themselves, or are otherwise destroyed.

● Water worlds are common.

● The physics/technology for vast space travel does not exist.

● The needed resources do not exist.

● The societal motivation for colonization does not exist.

● Intelligent species remain quiet (c.f. Stephen Hawking).

How did the history of life factor into the development of the geologic time scale? Think in terms of the origination and extinction of animals through time.

The earth has given us layers meaning you can see the evidence for early signatures of life up until our own level

How old, roughly, is the oldest evidence for animal life on Earth?

720 Ma

What is the Drake Equation designed to assess?

Number of civilizations with whom we could

potentially communicate; based on the notion that we will communicate to other civilizations

Frank made up this equation in order to promote discussion, not necessarily make it work and actually count the number of civilizations.

Do most stars have planets?

Yes, most stars have planets but it does not mean that they are all habitable

What kinds of measurements are used in the Drake Equation?

R* = rate of star formation in galaxy

fp = fraction of stars with planets

ne = average number of habitable planets per star

flife = fraction of habitable planets that develop life

fint.life = fraction of habitable planets with intelligent life

fciv = fraction of civilizations that can communicate

L = length of time that civilization survives

How old is the oldest evidence for eukaryotic life on Earth?

1.6-7 Billion years ago eukaryotic life

Understand the basic differences between prokaryotic and eukaryotic life.

eukaryotic: have membrane bound organelles, especially the nucleus, which contain genetic material

prokaryotic: do not

What are specific examples of bio-essential elements?

Hydrogen, Helium, Oxygen

What process explains the abundance of bio-essential elements across the universe?

Star formation

What is happening to the concentration of bio-essential elements in the universe over time?

Heavier elements become more available, as a result of helium capture

By what process do stars generate energy ?

Nuclear fusion

A star is on the main sequence

When it is still fusing hydrogen

When a star runs out of hydrogen

It becomes a red giant and starts fusing hydrogen with helium

In the process of helium capture

Helium fuses with heavier elements, so the temperature is very high in the core

What is a Super Nova

A super nova occurs when a star stops fusing elements and essentially collapses on itself, and sending materials out in an explosion

Where are stars born ?

Nebulae

Why do rocky planets tend to form close to their host star?

Rocks and metals form in hotter areas

Why do giant planets tend to form far from their host star

Ices and gaseous material tend to form in colder regions