5.2 - The Co-evolution Of Earth Adn Life

Question 1

How did the earth form?

Answer 1

The earth accreted slowly from comets/asteroids, but puzzling evidence from Apollo missions suggests the impact rate increased to 3.9 billion years ago. This is because we can see marls and creators on the moon which date back to this.

Question 2

What do formation models suggest?

Answer 2

Formation models suggest the impact flux would drop off exponentially, but the moon and mars show evidence for much bigger impacts around 3.8Ga

Question 3

When did earths surface environments become habitable and inhabited?

Answer 3

The best current evidence is from 3.43 Ga with less well accepted claims from 3.8 Ga (earths first sediments).

There are 2 key questions for AB when earths surface environments became permanently habitable and or permanently inhabited:

1) If earth was habitable since 4.56 Ga (after magma ocean from moon forming impact solidified), but only inhabited from 3.5Ga, this has a far different implication for life in the universe than:

(This implies that it was hard to create life in evolution)

2) If earth was habitable since the end of the LHB at 3.85 Ga, but inhabited from 3.8 Ga

(Only become habitable after earth became habitable = implies the creation of simple life isn’t that hard to create)

Question 4

How has the earths surface remained habitable since the onset of life?

Answer 4

It is the right distance from the Sun, it is protected from harmful solar radiation by its magnetic field, it is kept warm by an insulating atmosphere, and it has the right chemical ingredients for life, including water and carbon

Question 5

What is the faint young sun paradox?

Answer 5

Earth’s surface temperatures have remained within a narrow, habitable range of its history (At least since the onset of life)

This is despite large changes in the suns brightness

Greenhouse gas concentrations/compositions must have adjusted to counteract these changes
- > GHG must have had a higher effect and dismissed as the sun got brighter, enabling earth to have habitable environments.

(If GH and albedo were the same as they were today then earth would have been be below freezing temps with no liquid water on earth)

Question 6

What has the metabolisms of microbial life done?

Answer 6

The metabolisms of microbial life have radically changed the chemistry of earths atmosphere.

Life <—-> environmental conditions

In turn this has shaped the metabolisms employed by life.
Metabolism = the chemical changes occurring within a cell to:

1. Acquire elements and build them into biological materials (ie. Cell growth)
2. Generate energy
3. Excrete waste products

Question 7

What are the 2 major reactions that eukaryotes are reliant on?

Answer 7

Photosyntheses
C02 +H2O —> CH2O + O2

Respiration
CH2O + O2 —> CO2 + H2O

They both produce waste products.
Photosynthesis is where are all the oxygen in the atmosphere comes from.

(Prokaryotes are reliant on other reactions)

Question 8

What was the atmosphere before life like?

Answer 8

Atmosphere would be mostly volcanic gases
H2, H2O, CO2, N2, SO2, H2S

Earths interior was more radioactive, leading to higher CO2 and H2 concentrations than present.

No oxygen in atmosphere!! Oxygen in todays atmosphere is produced by a specific metabolism - oxygenic photosynthesis

Question 9

What were the metabolisms of early life on earth?

Answer 9

Earliest prokaryotic life is the closest root to LUCA

Methanogens and anoxygenic photosynthesis took place in early life and appear near the root of the tree of life.

Many early metabolisms tend to make CH4. They would produce methane and so the atmosphere was high in CH4

CH4 is a GHG that is 26x more potent than CO2

Question 10

What is the equation in methanogenesis?

Answer 10

4H2 + CO2 —> CH4 + 2H2O

Volcanic gases —-> methane and water

Biology is a significant source of CH4 to the early atmosphere

Question 11

Equation of anoxygenic photosynthesis (primary producers)

Answer 11

2 H2S + CO2 = hv —> CH2O + H2O + 2S-

2 H2 + CO2 + hv —> CH2O + H2O

Doesn’t produce oxygen

Question 12

What reactions did heterotrophic prokaryotic life use?

Answer 12

They used chemical reactions
Eg. Fermentation which was the only option for prokaryotes

Question 13

Why was earths early atmosphere periodically hazy?

Answer 13

It was a methane-rich haze, similar to saturns moon titan, but derived from biology

= as biology was the significant source of CH4 to the early atmosphere

Question 14

How did the early life have a profound affect on the atmosphere and climate?

Answer 14

Early metabolisms likely resulted in a methane (CH4) rich atmosphere

Enhanced greenhouse effect could have helped to compensate for the lower solar luminosity during the early earth history to maintain habitable temperatures.

Methanogens = will have turned CO2 into methane. Heating earth and so earth was warmer even though sun wasn’t as bright

Question 15

Oxygenic photosynthesis

Answer 15

It uses light to split water. It requires a huge amount of energy input to split water and is a very complicated molecular machinery to split H2O. Photosynthesis was a key critical step in the evolution of life and implications are huge when shaping evolution of life.

2H2S + CO2 + hv —> CH2O + H2O + O2

As H2O, CO2 and sunlight are everywhere, primary productivity would have increased dramatically.

Question 16

When did oxygenic photosynthesis evolve?

Answer 16

Carbon isotope signature of Rubisco

Resemblance of microfossils to Cyanobacteria (and of stromatolites to modern Cyanobacterial structures)

Biomarkers thought to be unique to Cyanobacteria (or to require O2 in their synthesis)

There are multiple lines of evidence to point to 2.7 Ga, but no one piece is individually conclusive for when oxygenic photosynthesis evolve.

• Undisputable proof is evidence of O2 building up in the environment ( 1 Ga after first microbial life and Defo’s by 2.3 Ga oxygen was building up in the atmosphere)

Question 17

What evidence is there for low O2 conditions?

Answer 17

There are rounded siderite/ uraninite / pyrite. The rounded grains indicate long term transport in rivers or beaches.

These particular minerals dissolve in O2-rich water and so the only way for them to be preserved is if there was no oxygen in the atmosphere.

Their existence implies that the waters they were tumbled in did not have much dissolved oxygen.

Question 18

What are O2 proxy - red beds?

Answer 18

They form near surface fluivial features showing evidence of iron oxidation. Evidence of this appears around 2.2 Ga.

When iron is exposed to oxygen it is oxidised and these red units show oxygen rich atmosphere.

Question 19

Where do ‘weird’ sulphur isotope patterns form?

Answer 19

They only form in oxygen free atmosphere

There would be no ozone layer to protect from UV rays. No UV is blocked and so Sulfur dioxide reacts with UV which causes isotopic reactions.

There was an oxygen poor/CH4 rich atmosphere prior to 2.3 Ga (older).

There was an oxygen rich/CH4 poor atmosphere from 2.3 Ga to the present. This rise in oxygen was the most profound transition in earths history Great Oxidation Event (GOE)

Question 20

When was the GOE?

Answer 20

GOE took place 2.32 Ga and oxygen went from trace levels to 5% modern

The rise of atmospheric oxygen resulted in the decline of atmospheric CH4.

Can’t have an atmospheric rich in both CH4 and O2 as they react with each other and so can’t have a 50/50 split.
O2 won this and so took over in the atmosphere. This lead to a period where the planet got very cold.

Question 21

What was the GOE?

Answer 21

It was the most substantial re-organisation of biochemical cycles in earth history

• Climate = collapse of methane greenhouse, perhaps linked to global glasciations
• Chemistry = oxygenation of the oceans changed what life could live there

It lead to a mass extinction as organisms should not cope with O2 and was poisonous to many early life forms. It killed all the methanogens. But this revolution in earth caused by the evolution of oxygenic photynthesis paved the way for the next major revolution in life = eukaryotes

Question 22

Late Proterozoic timeline

Answer 22

The Late Proterozoic Era, also known as the Neoproterozoic Era, spanned from approximately 1 billion to 541 million years ago. It was a time of significant geological, biological, and climatic changes on Earth, including the emergence of complex life forms.

Here is a brief overview of the Late Proterozoic timeline:

Tonian Period (1 billion to 720 million years ago):
The period is named for the Tonian Supergroup in Western Australia.
The first evidence of eukaryotic life, organisms with complex cells, appears.

The supercontinent of Rodinia formed, and global glaciations occurred towards the end of the period.
Cryogenian Period (720 million to 635 million years ago):
The period is named for the extensive glaciations that occurred during this time.
The earliest known animals, including sponges and jellyfish, appear in the fossil record.
The supercontinent of Rodinia began to break up.
Ediacaran Period (635 million to 541 million years ago):
The period is named for the Ediacara Hills in South Australia, where many important fossils have been found.
The first complex, multicellular organisms appear, including some of the earliest animals with hard shells and skeletons.
The supercontinent of Rodinia continued to break up, leading to the formation of smaller continents.
The first evidence of sexual reproduction appears.

Overall, the Late Proterozoic was a time of major evolutionary and environmental changes, with the emergence of complex life forms and the breakup of supercontinents. These changes set the stage for the explosion of biodiversity that occurred during the subsequent paleozoic era.

Question 23

Why did eukaryotes take so long after the GOE to evolve and radiate

Answer 23

The Great Oxidation Event (GOE), which occurred approximately 2.4 billion years ago, marked the first time that significant amounts of oxygen appeared in Earth’s atmosphere. The presence of oxygen was a key factor in the evolution of eukaryotic organisms, which are characterized by complex cells with internal structures such as mitochondria and a nucleus. However, it took a long time after the GOE for eukaryotes to evolve and radiate.

There are several factors that may have contributed to this delay:

Oxygen toxicity: Although oxygen was necessary for the evolution of eukaryotes, it was also toxic to many organisms that had evolved in an anaerobic environment. It took time for organisms to develop mechanisms to detoxify oxygen and use it for energy.

Prokaryotic competition: Before eukaryotes could evolve, they had to compete with prokaryotic organisms that dominated the early Earth. Prokaryotes had already evolved a range of adaptations that allowed them to thrive in different environments, making it difficult for eukaryotes to establish a foothold.

Complexity: The evolution of eukaryotes required the development of complex cellular structures and mechanisms, such as the endomembrane system, which allows for the segregation of different cellular functions. This level of complexity may have taken a long time to evolve.

Environmental changes: The environment of the early Earth was constantly changing, with fluctuations in temperature, atmospheric composition, and ocean chemistry. These changes may have created barriers to the evolution of eukaryotes, particularly if they required specific environmental conditions to thrive.

Overall, the evolution of eukaryotes was a complex and multifaceted process that took a long time to unfold. It required the development of new adaptations, the ability to compete with existing organisms, and the persistence to survive in a constantly changing

Question 24

Why were oxygen levels held back?

Answer 24

Due to carbon and sulphur cycle.

Question 25

When was there a second increase in atmospheric oxygen?

Answer 25

It is associated with severe global glaciations.
- 2nd oxidation event in Phanerozoic

The oxygen increase correlated to formation of complex life. Animals require at least 10% oxygen in atmosphere.

Question 26

Archaea vs Proterozoic vs Phanerozoic oxygen states

Answer 26

Archaea = oceans were anoxic and iron rich. There was no Sulfur cycle (archae and bacteria)

Proterozoic = surface oxic, deep water anoxic-sulfidic (eukaryotes and fungae)

Phanerozoic = oceans oxic sulfate-rich (eukarya, fungae, archae, bacteria, plants and metazoa)

Question 27

The Cambrian Explosion

Answer 27

The Cambrian explosion was a period of rapid evolutionary diversification and the emergence of many major animal groups that occurred approximately 541 million years ago during the Cambrian Period. During this time, there was a sudden burst of diverse and complex animal forms that appeared in the fossil record, many of which were the first representatives of modern animal phyla.

Before the Cambrian explosion, the fossil record of animal life was dominated by small and simple organisms such as sponges, cnidarians, and mollusks. However, during the Cambrian explosion, there was a sudden proliferation of more complex and diverse forms of animal life, including arthropods, echinoderms, and chordates. This rapid diversification of life forms occurred over a relatively short period of time, on the order of several million years.

The causes of the Cambrian explosion are still not fully understood, but several factors have been proposed, including changes in ocean chemistry, environmental and ecological factors, and genetic innovations. It is likely that a combination of these factors contributed to the explosion of biodiversity that occurred during this time.

The Cambrian explosion is a significant event in the history of life on Earth because it marks the emergence of many of the animal groups that dominate the modern biosphere. It also provides valuable insights into the evolutionary processes that drive the diversification of life and the emergence of new biological forms.

Question 28

Phanerozoic diversity

Answer 28

The Phanerozoic Eon, which began approximately 541 million years ago and continues to the present day, is the most recent eon in Earth’s history. It is characterized by the emergence and diversification of complex life forms, including animals, plants, and fungi, and is divided into three major eras: the Paleozoic, Mesozoic, and Cenozoic.

During the Phanerozoic Eon, there has been a dramatic increase in the diversity of life on Earth. This diversification is particularly evident in the fossil record, which shows a succession of major radiations and extinctions. These events have led to the emergence of new biological forms and the extinction of others, resulting in the complex web of life that exists today.

The Paleozoic Era, which lasted from approximately 541 million to 252 million years ago, was characterized by the emergence and diversification of many major animal groups during the Cambrian explosion, as well as the emergence of terrestrial plants and the colonization of land by animals. This era was also marked by several major extinction events, including the end-Permian extinction, which was the largest mass extinction in Earth’s history.

The Mesozoic Era, which lasted from approximately 252 million to 66 million years ago, was characterized by the emergence and diversification of dinosaurs, as well as the evolution of flowering plants and the emergence of modern mammals. This era also saw the extinction of the dinosaurs at the end of the Cretaceous Period, which was caused by a catastrophic event, likely a meteorite impact.

The Cenozoic Era, which began approximately 66 million years ago and continues to the present day, has been characterized by the diversification and expansion of mammals, as well as the emergence of modern birds and the evolution of humans. This era has also been marked by several major extinction events, including the end-Paleogene extinction, which led to the extinction of the non-avian dinosaurs and the rise of mammals as the dominant land animals.

Overall, the Phanerozoic Eon has been a time of rapid diversification and change, marked by the emergence and extinction of many biological forms. This diversification has led to the complex and diverse web of life that exists on Earth today.

Question 29

Phanerozoic timeline

Answer 29

The Phanerozoic Eon is the most recent eon in Earth’s history, spanning from about 541 million years ago to the present day. It is divided into three major eras, each marked by significant events in the evolution of life on Earth. Here is a brief overview of the Phanerozoic timeline:

Paleozoic Era (541 to 252 million years ago)
Cambrian Period (541 to 485 million years ago): During this time, there was a rapid diversification of marine life, known as the Cambrian Explosion. Many of the major animal phyla that exist today first appeared during this time.
Ordovician Period (485 to 444 million years ago): The first land plants appeared, and jawless fish and early vertebrates became more diverse.

Silurian Period (444 to 419 million years ago): The first vascular plants and terrestrial arthropods appeared, and jawed fish became more common.

Devonian Period (419 to 359 million years ago): The first amphibians appeared, as well as early sharks and bony fish. Land vertebrates began to diversify.

Carboniferous Period (359 to 299 million years ago): The first reptiles appeared, and coal deposits were formed from large swamp forests.
Permian Period (299 to 252 million years ago): The most severe mass extinction in Earth’s history occurred at the end of the Permian, wiping out about 96% of marine species and 70% of land species.
Mesozoic Era (252 to 66 million years ago)
Triassic Period (252 to 201 million years ago): The first dinosaurs appeared, as well as the first mammals, turtles, and crocodiles.

Jurassic Period (201 to 145 million years ago): Dinosaurs became dominant on land, and birds evolved from small theropod dinosaurs.

Cretaceous Period (145 to 66 million years ago): Flowering plants (angiosperms) became widespread, and the largest dinosaurs, such as the Tyrannosaurus rex and Triceratops, lived during this time. The Cretaceous ended with a mass extinction event that wiped out the non-avian dinosaurs.
Cenozoic Era (66 million years ago to present day)

Paleogene Period (66 to 23 million years ago): Mammals underwent a rapid diversification, and early primates and whales appeared.

Neogene Period (23 to 2.6 million years ago): The first hominins (early humans) appeared, and many modern mammal groups (such as elephants, giraffes, and cats) evolved.

Quaternary Period (2.6 million years ago to present day): Humans evolved and began to spread across the globe, and the last ice age occurred before ending around 10,000 years ago.

The Phanerozoic timeline is characterized by the emergence and diversification of complex life forms, as well as by several major mass extinction events that have shaped the course of evolution on Earth.

Question 30

Timeline of earliest land plants

Answer 30

Spores= from 475 Ma

First fragments of plants = 450 Ma

Vascular plants = from 425 Ma

Leaves and roots = 420 Ma

Trees = 385 Ma

Large forests = 375 Ma

Question 31

What are CO2 proxies and predictions

Answer 31

Carbon dioxide (CO2) proxies are methods used to estimate past atmospheric CO2 concentrations based on indirect measurements from sources such as ice cores, fossilized plant tissues, and sedimentary rocks. These proxies allow scientists to reconstruct changes in CO2 levels.

Models and data agree that CO2 was much higher for most of the Phanerozoic and possibly as high as 10-20x modern prior to the evolution of plants

(Earliest land plants pulled down co2 and cooled the planet)

Question 32

What are the 5 mass extinctions

Answer 32

The five mass extinctions are major events in the history of life on Earth, each of which resulted in the extinction of a significant proportion of the planet’s species. Here is a brief explanation of each of the five mass extinctions:

1. End-Ordovician (443 million years ago): This mass extinction was caused by a series of glaciations that led to a drop in sea levels and a loss of shallow marine habitats. It is estimated that up to 85% of marine species were lost during this event.
2. Late Devonian (359 million years ago): This extinction event was likely caused by a combination of factors, including climate change, sea-level fluctuations, and the evolution of new predator-prey relationships. It resulted in the loss of around 75% of all species, with many coral and brachiopod species disappearing from the fossil record.
3. End-Permian (252 million years ago): This was the most severe mass extinction in Earth’s history, with around 95% of all species going extinct. It was likely caused by a combination of factors, including massive volcanic eruptions, climate change, and ocean acidification.
4. End-Triassic (201 million years ago): This event resulted in the loss of around 80% of all species, including many large amphibians and reptiles. It was likely caused by a combination of climate change and the eruption of massive volcanic systems.
5. End-Cretaceous (66 million years ago): This is perhaps the most famous mass extinction, as it led to the extinction of the dinosaurs. It was likely caused by the impact of a large asteroid or comet, which triggered massive wildfires, tsunamis, and a global winter. Around 75% of all species went extinct during this event.

Question 33

What caused the late Permian extinction?

Answer 33

The Late Permian extinction, also known as the End-Permian extinction, was the most severe mass extinction event in Earth’s history, with around 95% of all species becoming extinct. The exact cause of the extinction is still not fully understood, but scientists believe that it was likely the result of a combination of several factors, including:

Extinction of families = 49% marine, 63% terrestrial, 61% total

Massive volcanic eruptions: The eruption of the Siberian Traps, a large volcanic province in what is now Russia, is believed to have released massive amounts of greenhouse gases into the atmosphere, leading to global warming and ocean acidification.

Climate change: The release of greenhouse gases from the Siberian Traps is believed to have led to a rapid increase in global temperatures, which would have had a significant impact on the Earth’s ecosystems.

Ocean anoxia: As the Earth’s oceans warmed and became more acidic, they may have become depleted of oxygen, leading to widespread anoxia (lack of oxygen) in the oceans. This would have had a devastating impact on marine ecosystems.
Impacts from space: There is some evidence to suggest that impacts from space, such as a comet or asteroid, may have also played a role in the extinction event.

Overall, the Late Permian extinction was likely the result of a combination of several factors, including volcanic activity, climate change, ocean acidification, and possibly impacts from space. The exact sequence of events that led to the extinction is still the subject of ongoing scientific research and debate.

Question 34

What went extinct in the KT extinction?

Answer 34

Cretaceous - Tertiary (KT) extinction caused 60-80% of marine species to die, plus a number of terrestrial plants and animals.

Killes the dinos

Question 35

When was there a rise of mammals?

Answer 35

After the KT extinction, mammals diversified. Wouldn’t have radical changes in the evolution of life without extinctions. Mammals appeared in the late Triassic, but there were small rodent-like creatures at the end of the Mesozoic

They greatly diversified in the cenozoic.

Question 36

What have hominids evolved in response to?

Answer 36

Hominids have evolved in response to (and created) changes in climate

Earth fluctuated between cold and warm periods - we are in an interglacial period right now.

Question 37

Could the stable climate enable agricultural revolution?

Answer 37

Agricultural revolution = last 10,000 years. Holocene is a stable period in the climate and we have been able to develop agricultural and civilisation.

It is possible that a stable climate played a role in enabling the agricultural revolution to occur, but it is important to note that the relationship between climate stability and the development of agriculture is complex and multifaceted.

A stable climate would have provided more consistent rainfall patterns, making it easier for farmers to plan their crops and manage water resources. A stable climate would also have provided a more stable environment for early domesticated crops and animals to grow and reproduce.

Question 38

Summary

Answer 38

Life has radically altered the trajectory of the earth, and vice-versa

• The origin of life modified the composition of the atmosphere and oceans, as did the later origin of oxygenic photosynthesis, eukaryotes and animals

Question 39

How is the evolution of intelligence a similar revolution to the ones in earths history?

Answer 39

The evolution of intelligence is somewhat similar to the five mass extinctions and the agricultural revolution in that it represents a major shift in the trajectory of life on Earth. However, there are also important differences between the evolution of intelligence and these other events.

The five mass extinctions and the agricultural revolution represent major changes in the global ecosystem and the relationship between humans and the natural world. In contrast, the evolution of intelligence is a more focused change that occurred within a particular lineage of organisms, specifically the hominids.

The evolution of intelligence is characterized by the development of higher cognitive abilities, including the ability to reason, communicate, plan, and innovate. This development is thought to have allowed hominids to adapt to changing environments, develop more sophisticated social structures, and ultimately, develop modern human civilization.

While the evolution of intelligence is a significant event in the history of life on Earth, it is important to note that intelligence has evolved in a wide range of organisms, not just hominids. For example, birds, primates, dolphins, and even some insects have demonstrated high levels of cognitive ability, suggesting that intelligence is a complex and multi-faceted trait that has evolved independently in multiple lineages.

Therefore, while the evolution of intelligence is similar to other major events in the history of life on Earth in that it represents a significant shift in the trajectory of life on this planet, it is also a unique and complex phenomenon that has evolved in a variety of different ways and in multiple lineages.