Lecture 25: The Archean Biosphere

Question 1

What are the four things the first cells needed to create?

Answer 1

1) Proteins
2) Nucleic acids
3) Carbohydrates
4) Lipids

Question 2

What is the differentiation of Earth?

Answer 2

The organization of Earth into layers (core, mantle, and crust) due to gravity.

Question 3

What are komatiites?

Answer 3

Rocks formed from ultramafic lavas once temperatures dropped below 1000°C

Question 4

How old is the oldest rock?

Answer 4

4.0 Gyr (billion years)

Question 5

What was the atmosphere like on early Earth?

Answer 5

• High Co2 levels (10 bars)
• High greenhouse gases
• No free O2

Question 6

What is the ‘Organic Soup’ model of how organic compounds may have arisen?

Answer 6

Key prebiotic monomers were formed when reduced gases in the atmosphere were subject to UV irradiation and electrical discharges.
-They then condensed to form more complex compounds, such as amino acids, which accumulated into seawater.

Question 7

What was one major problem with the ‘Organic Soup’ model?

Answer 7

Giant impacts would have constrained the timing of life’s origin at the Earth’s surface.
-Impacts would have vaporized rock and evaporated the upper water column, and perhaps the entire ocean

Question 8

What is the most accepted theory on how life arose on Earth?

Answer 8

The theory that states that life would have started around hydrothermal vents
-Minerals surfaces could have served as templates for further polymerization reactions

Question 9

Where does evidence for ancient life come from?

Answer 9

• Microfossils
• Biogenic structures
• Isotopes
• Biomarkers

Question 10

What are microfossils?

Answer 10

The preservation of fossils that are microscopic in size.

Question 11

Why are stromatolites (biogenic structure) the best piece of evidence for ancient life?

Answer 11

Because bacteria get buried under sediment then want light so the bacteria grow upwards, causing columns in the stromatolites.
-The columns are proof of bacteria

Question 12

What is oxygenic photosynthesis?

Answer 12

Photosynthesis with oxygen

Question 13

What is anoxygenic photosynthesis?

Answer 13

Photosynthesis without oxygen

Question 14

How are Microbially Induced Sedimentary Structures (MISS) formed?

Answer 14

By microbial mates of filamentous bacteria trapping siliciclastic sediments in more
energetic tidal flat settings.

Question 15

What important about MISS

Answer 15

• Can go back to 3.2Gyr

- Can see structures in the rock record that look like bacteria that would grow on river beds

Question 16

How are isotopes evidence for ancient life?

Answer 16

Because the transformation of inorganic carbon via autotrophic pathways into organic carbon involves the preferential incorporation of the lighter isotope, into the organic phase, leaving behind a reservoir enriched in the heavier isotope.

Question 17

How are biomarkers evidence for ancient life?

Answer 17

-They retain some resemblance to the original biological molecule, even after a long history of decomposition

Question 18

What are biomarkers?

Answer 18

Organic compounds derived from more complex precursors to provide information on their relative abundance in ancient environments.

Question 19

When did cyanobacteria evolve?

Answer 19

Ranges from 3.5 to 2.7 billion years ago

Question 20

Why are cyanobacteria important?

Answer 20

They learned to split water to generate reducing power to fix CO2, and in doing so, released free oxygen to the environment

Question 21

When did oxygen accumulate in the atmosphere?

Answer 21

According to the rock record, around 2.5 Gyr

- “The Great Oxidation Event”