a young Earth, fit for early life

Question 1

conditions of the early earth (4 billion years ago)

Answer 1

• 20% less bright
• high rates of meteor bombardment
• far more oceanic crust than continental crust
• no free O2
• no Ozone layer to shield Earth’s surface from the Sun’s UV radiation

Question 2

how could liquid water exist on the early Earth with a fainter sun?

Answer 2

-the atmosphere was significantly richer in greenhouse gases
(NOT O2)

-called “The Faint Young Sun Paradox”

Question 3

what do the textures of sedimentary rocks tell us?

Answer 3

• tells us the about the environment in which they were deposited.
• i.e. if it was windy, hot, wet, cold

Question 4

biomarkers

Answer 4

• Carbon-rich compounds that are only known to be produced by life, or by their specific degradation products
• graphite is not one
• in Archean cherts contain microfossils

Question 5

geological mapping

Answer 5

-critical to establish the context and type of sedimentary deposit in which the signs of life are found

Question 6

radiometric dating

Answer 6

-constraining the absolute age of the sedimentary rocks by measurements from the most reliable grains in the neighbouring igneous rocks

Question 7

visual observations

Answer 7

-microscope, scanning electron microscope, transmission electron microscope

Question 8

chemical analysis

Answer 8

-establish if chemistry is correct for life

Question 9

isotopic analysis

Answer 9

-look for characteristic ratios of stable isotopes of carbon, sulfur and nitrogen selected by microbial life

Question 10

panspermia theory

Answer 10

-the origin of life on Earth is actually from another planet or space itself

Variations:

1. Amino acids on meteorites are exposed to energy in space in the form of ultraviolet light
   - Evolve into simple cells in space → simple cells are then delivered to earth through falling meteors
2. Amino acids from meteorites are delivered to earth → they develop into cells according to primordial soup theory
   - Simple cells evolve on a different planet and then transported to earth on a meteorite

Question 11

experimental support for Panspermia Theory

Answer 11

-some forms of organic life can persist in space
(Bacterial spores, lichens and DNA can persist in space IF protected from UV radiation)

-Murchison meteorite contained 90 different amino acids, 19 of which are found on Earth

Question 12

Issues with the Panspermia Theory

Answer 12

Does not solve the issues inherent with the primordial soup theory

• How do cells arise?
• How did polymers form from monomers?

Does not solve the issue of how life would have evolved on the other planet

Question 13

formation of amino acids

Answer 13

cannot form if reactive O2 is present

Question 14

banded iron formations

Answer 14

• thick deposits of Fe2O3

- these layers are chemical precipitates in oceans

Question 15

explain the process of banded iron formations

Answer 15

1. bacteria photosynthesize in shallow water, releasing O2, which is carried by ocean currents (some lost to the atmosphere)
2. ocean currents mix this O2 with Fe2+ rich water
3. Fe2O3 grains precipitate and settle as a layer on the seafloor

Question 16

oxygen build up

Answer 16

-the ratios of Fe isotopes in banded iron formations
suggest that other bacteria may have also participated in their formation

-as anaerobic bacteria oxidized dissolved Fe to get energy, the O2 produced by cyanobacteria could have started accumulating more widely in atmospheres and oceans

basically this suggests that bacteria were the cause of Oxygen build up in the atmosphere

Question 17

red beds

Answer 17

• were common after 2Ga, a sign of oxidation!
• basically the quartz grain in the sandstone becomes coated in Fe2O3 from chemical weathering, “rust” in red/yellow/brown Fe-rich oxide compounds

Question 18

towards the end of the Great Oxygenation Event:

Answer 18

• diverse microfossils of bacteria become more common in chert
• most likely were prokaryotes
• cannot tell much bc organelles and DNA are not preserved

Question 19

Eukaryotes and Multicellularity

Answer 19

• arrive 1.8 Ga

- took so long because they all require some O2