Life 'bottom-up'

Question 1

State 2 arguments against the top-down approach to origins research

Answer 1

1. Due to plate tectonics (started 3 Ga) we are running out of rocks, earliest crustal rocks 4 Ga
2. Ancient terrains subject to ‘preservation bias’ where rocks surviving that long likely have special properties and so are not representative of all rocks at the time period

Question 2

What are the components of the Miller-Urey experiment? What does the experiment do?

Answer 2

Water, electric sparks, NH3, CH4, H2, H20
Simulates an early Earth atmosphere, produced amino acids proving that biomolecules can form under these conditions and confirmed the idea that life came from chemistry.

Question 3

What are the criticisms of the Miller-Urey experiment?

Answer 3

The ancient atmosphere was most likely weakly reducing and dominated by N2 and CO2, with UV as the most common radiation source

Question 4

How did the formation of the Earth’s core change volcanic gases?

Answer 4

H2, CH4, NH3 ==> H2O, CO2, N2 with minor H2 and CO

Question 5

Why is it significant that the moon has a similar composition to the Earth’s mantle?

Answer 5

Suggest that the impact between Earth and Theia occurred after the core had differentiated, and so origin of life would not have coincided with Miller-Urey gases

Question 6

Describe the mechanism by which ribose could be made in space

Answer 6

• on a dust particle encapsulated by an ice mantle (ice analog)
• if methanol, ammonia and water were attached
• under UV radiation

Question 7

How did Jennifer Blank replicate the conditions for a comet impact? What did she find?

Answer 7

• Used a giant gun to shoot impactor in to a big tank of felt
• Found that the force of impact actually generated more complex pre-biotic molecules, hence there is the implication that pre-biotic molecules should accumulate on most planetary surfaces

Question 8

Why do hydrothermal vents present a promising location for the origin of life? Give 5 reasons

Answer 8

• Globally distributed
• Geochemically reactive environment
• Rich microbial communities
• Their H2-CO2 chemistry is very similar to that of prokaryotic autotrophs (these are anaerobic chemotrophs)
• Protected from the effect of large impacts and harsh UV conditions??

Question 9

Give an example of an inorganic reaction, catalyzed by a mineral which produces energy

Answer 9

Fe-sulfides:

FeS (s) + H2S (g) –> Pyrite + H2 + electrons (for energy)

Question 10

What property of mineral surfaces may be important when forming molecules?

Answer 10

• some have chiral surfaces and so have ‘face-specific’ absorption properties

Question 11

What is the Wächtershäuser theory?

Answer 11

That, as Fe/Ni/S enzymes are at the heart of many metabolic reactions, maybe proto-metabolism started on a Fe/Ni/S mineral
However, criticism for lack of a ‘realistic’ environment

Question 12

Many of the most ancient microbes are hyperthermophiles. What 2 possibilities does this present?

Answer 12

1. That life originated in a high temperature environment?

2. Or simply that hyperthermophiles survived evolutionary bottle-necks more easily