The Development of Life on Earth

Question 1

What is the central dogma of biology?

Answer 1

The flow of genetic information in all biological cells. Specifically RNA to DNA in 3 processes:
1. Transcription
2. Translation
3. Replication

Question 2

What are the 4 things about water that make it a necessity for biological growth?

Answer 2

1. Universal solvent
2. Ability to dissociate molecules into positive and negative ions, critical for biochemical reactions
3. Osmosis
4. Maintaining cell shape and cell membranes

Question 3

What is the name for an organism who thrives in <20℃?

Answer 3

Psychrophiles.

Question 4

What is the name for an organism who thrives in 15-45℃?

Answer 4

Mesophiles

Question 5

What is the name for an organism who thrives in 45-80℃?

Answer 5

Thermophiles

Question 6

What is the name for an organism who thrives in >80℃?

Answer 6

Hyperthermophiles.

Question 7

What is the name for an organism who thrives in pH of 5-9?

Answer 7

Neutrophiles

Question 8

What is the name for an organism who thrives in pH of <2?

Answer 8

Acidophiles

Question 9

What is the name for an organism who thrives in pH of >10?

Answer 9

Alkaliphiles

Question 10

What are the nutrients required for life?

Answer 10

Carbon, mainly. Autotrophs convert inorganic carbon into organic, and heterotrophs consume this.
Metals are also required.

Question 11

What was earths primordial soup?

Answer 11

Biologically important molecules such as methane, ammonia, water and hydrogen self assembling into simple living cells.

Question 12

Describe the RNA world hypothesis.

Answer 12

• RNA molecules catalyse replication, meaning they can perpetuate their own evolution. They compete and the best lives on.
• Chemical pathway discovered that RNA nucleobases were found in primordial soup that had been wet and dried.

Question 13

What are the unsolved questions for the RNA world hypothesis?

Answer 13

1. Unclear on if RNA or proteins came first
2. No energy source

Question 14

What is the geological support for RNA world?

Answer 14

The wet and dry cycles promote necessary reactions to form polymer. However there is no record of a stable wetting and drying environment.

Question 15

Describe the Metabolism hypothesis.

Answer 15

• Chemical gradients needed life as a series of self sustaining chemical reactions that produced biomolecules
• Would have provided molecules and energy needed to fuel them
• Primitive bacteria were then chemosynthetic thermophiles

Question 16

What are the unsolved issues with the Metabolism first hypothesis.

Answer 16

There is no way to store genetic information to pass on through evolutionary processes.

Question 17

What is the geological support for the metabolism first hypothesis?

Answer 17

• Hydrothermal alkaline vents with hot temperatures, energy gradients, biochemical compounds and metals.
• These can produce protocells with iron sulphide membranes
  However there is no clear link for how it all ended up in a single walled membrane to form a prokaryotic cell.

Question 18

What are the defining characteristics of prokaryotes?

Answer 18

• No membrane bound organelles
• 70s ribosomes
• Asexual reproduction via binary fission

Question 19

What are the differences between bacterial and Archean cell membranes?

Answer 19

Archaeal cell walls have isoprene chains that makes them able to withstand extremes.
- They also lack peptidoglycan which bacteria have an use for strength

Question 20

What are the defining characteristics of Archaea.

Answer 20

• S layers form cell walls combined with methanochroitin (very strong) and sheaths linking tubular proteins
• Have pseudomurein (stronger than peptidoglycan)

Question 21

What are Stromatolites?

Answer 21

• Bio sedimentary structures formed of microbes and sediments
• Form microbial mats from falling sediment, allowing for vertical growth
• Built by photosynthetic cyanobacteria

Question 22

What is the issue with stromatolites?

Answer 22

Easy to mismatch with other lines of evidence from biomarkers. They could be from abiotic prosses?

Question 23

What is the oldest Eukaryotic fossil?

Answer 23

Grypania, 2.1 Ga.
- Possibly cyanobacteria or algae
- Isn’t DEFINITELY a eukaryote

Question 24

What is the oldest uncontroversial Eukaryotic fossil?

Answer 24

Acritarchs. 1.8 Ga.
- Organic walled microfossils with complex wall ornamentation

Question 25

What is the oldest fossil tied to a modern group?

Answer 25

- Bangiomorpha pubescens, 1.05 Ga - Red algae - First evidence of sexual reproduction

Question 26

What are the three fossil types?

Answer 26

Body Trace Chemical

Question 27

What drove the snowball earth periods? What came out of them?

Answer 27

Driven by: Runaway albedo effect of expansion of ice sheets followed by volcanic emissions Arose: First complex animal fossils due to extreme selection pressure of fluctuating earth and limited habitats

Question 28

What is multicellularity defined by?

Answer 28

- Cell differentiation - Cell signalling - Co ordinated growth and development - Division of labour - Independent cells in an organism

Question 29

What were the first organisms to perform photosynthesis and what did they create?

Answer 29

Cyanobacteria performed in chloroplasts. - Evidence for this is fossilised bubbles in stromatolites which form reefs

Question 30

What is a proxy?

Answer 30

* Proxies are a measurable quantity of something that substitutes for something else that is no longer measurable

Question 31

What are the three proxies that help us constrain O2 over time?

Answer 31

1. Mass independent fractionation of sulphur isotopes 2. Iron redox geochemistry 3. Uraninite

Question 32

What is isotope fractionation?

Answer 32

When some chemical process partitions a mixed pool of isotopes into pools of unique ones.

Question 33

How were early sulphur isotopes fractionated?

Answer 33

- Sulphur gas oxidised to H²SO⁴ and rained out as sulphate - Sulphur gasses accumulated in the atmosphere and underwent photochemical reactions - These resulted in unique geochemical signatures resulting from mass independent fractionation

Question 34

How can we use these sulphur isotopes to detect oxygen amounts?

Answer 34

- Values of sulphur isotopes below/above 0 signify isotope fractionation - The process of sulphur gas being oxygenated cant occur without oxygen so there must have been oxygen if there is no MIF.

Question 35

Why are there no Red Beds before 2.2Ga?

Answer 35

Iron rich minerals were not oxidised and reduced iron weathered away into the ocean. When atmospheric O2 accumulated, iron rich soils were oxidised and turned to rust.

Question 36

Describe how Banded Iron formations form.

Answer 36

- Composed of alternating iron rich and iron layers of chert Increase when ocean oxygen makes iron oxides and then oxygen in the atmosphere rises, as well as when oxidative weathering of soil caused an increase of sulphur in the ocean. Increased again when iron was removed in a brand new geochemical pathway (snowball)

Question 37

What is Uranitite?

Answer 37

- Rare today as it is extremely sensitive to oxidation - So if there is any, there isn't any oxygen. - Forms clasts in sandstones.

Question 38

What new proxy appeared after plants?

Answer 38

Wildfire records, using charcoal. We use it to estimate minimum oxygen levels once it appears.

Question 39

What are the three evolutionary faunas according to John Sepkoski?

Answer 39

Cambrian, Palaeozoic and Modern Fauna.