Early Life

Question 1

What is ‘said to be’ the oldest evidence for life on earth?

Answer 1

Apex Chert: contains fossils that look like cyanobacteria. Dates to 3.5 Ga. However if we had photosynthesis here, life’s origin would be pushed back even further.

Fossils supported by William Schopf.
KEROGENOUS in composition - product of decay of bacterial cells.

Question 2

What is chert?

Answer 2

Microcrystalline quarts that forms in a lot of environments, often fine preservation of fossils (i.e. rhynie chert in scotland - devonian, can see individual cells of plants)

Question 3

What was the controversy about Apex chert?

Answer 3

Brasier said there were impurities in the chert, that they weren’t fossils, they were ‘smudges’
looked at depositional settings and said they would be around a deep oceanic vent, couldn’t possibly be photosynthetic!

The molecules looked like biology due to CO2 release at vent systems.

Braisier said they were ‘pseudo fossils’ not real fossils.

Question 4

What are Hydrobereccias?

Answer 4

fractures in surrounding rock due to heat. Water induced fractures will fill up with organics giving the impression of lifeforms.

Question 5

How did Schopf respond to the controversy of chert?

Answer 5

Accepts paleodepositonal model, used isotopic imaging technique to demonstrate cell like qualities in fossils. ***
ask nellima

Question 6

What is the Isua formation?

Answer 6

Pillow lavas off of Hawaii (dated 3.8 Ga), evidence of first standing water

Question 7

What is carbonic evidence for photosynthesis?

Additional evidence?

Answer 7

most of carbon is C12, photosynthesis uses this, so organic carbon contains lower 13:12 ratio than inorganic carbon. depleted c13 cause they don’t want it.

MICROFOSSILS at the Gunflint chert in ontario around 1.9 Ga. INdicates life must be back at like 3.45 Ga, at least. maybe even 4.1GA

Question 8

What is so special about zircon crystals?

Describe them

Answer 8

They grew in the sedimentary rocks of jack hills, and the oldest part of the crystal grew where liquid water interacted with PRE EXISTING continental crust to produce something similar to granite. This implies temp was much cooler than previously thought.

Question 9

What is the LHB and why is it an issue?

Answer 9

Late heavy bombardment period (4.1-3.8GA) would have enough impacts to evaporate all oceans and melt crust! We know this due to patterns in moons and surrounding planets.

Paradox: how did life evolve if this would have wiped out everything??

Question 10

How does the paradox of LHB get solved?

Answer 10

In archaea, there are extreme thermophiles (found deep (3.5km) and in hot water!)

• extremophiles can be in salty conditions or in nuclear waste.

Bascially these things lived in awful conditions and preserved the evolution of life!
Everyone has a common ancestor: thermophile archaea. Found in ocean crust.

Question 11

What is life from elsewhere called?

Answer 11

Panspermia

Question 12

how do we know meteorites are from mars?

What is the evidence that there are fossils on mars?

Is this evidence good?

Answer 12

Mars has a ‘fingerprint’
Fossil evidence
1) Rod shaped structures that look like bacteria
2) PAH (polycyclic aromatic hydrocarbons) common life chemicals
3) Magnetite crystals produced by bacteria. (use magnetite to align themselves)
4) Carbonate rosettes (dark spots indicating MG rich ores with iron carbonate and iron sulfide) - similar to bacteria produced by terrestrial pond bacteria.

Evidence is OKAY but:
its really really small, PAHs and Rosettes can form physically (not needing biology)
Magnetite is most convincing, but we don’t have evidence that they CAN’T be formed inorganically, they just don’t right now.

Question 13

What are mars hypothesis?

Answer 13

1. life evolves on earth, when it gets too hot life retreates into other environment, mars dies.
2. life evolves on mars first, then cools and dies faster than earth, but before it does that it sends life via meteorites to earth- we are all martians
3. life never evolved on mars.

Question 14

What was keeping earth warm when the sun was less luminous?

Answer 14

Methane Gases!
- methanogens (archaea and obligate anerobes) like bacteria that produces methane in their metabolism. Live without oxygen.

Live in marsh lands and in animal guts. Decompose organic mattter.

Reduce C02 to CH4

10x more effective than c02

would have made skies pink!

Question 15

What defines a conglomerate?

What are tilites?

Answer 15

erosion of preexisting lumps.
Tilite conglomerates are the produce of glacial activity.
Lake huron in ontario has deposits aged 2.2. GA.
Some of these tilites are equatorial, which is super weird.

Question 16

How did earth cool?

Answer 16

Removal of methane due to stromatolites, which produce oxygen. THis oxydizes the methane in the air to become c02 which is a less effective greenhouse gas, causing the earth to be cold
Albedo would cause postive feedback once it reached level of texas.

Question 17

Why eukaryotism good?

Answer 17

Sexual reproduction helps diversification, mixing of DNA, helps evolution speed up.

Question 18

What is endosymbiosis?

Answer 18

Popular theory of mitochondrian and chloroplasts in plants that were once freely living, and then were engulfed by a host, then developed a symbiotic relationship to make energy.

Question 19

What are acritarchs?

Answer 19

Fossil algae reported at 1.6 Ga.

Question 20

What are the first metazoans?

Answer 20

Earliest fossil multicellular eukaryotes.
Found at hunting formation in canada of 1.2 Ga.
The bangiomorpha show DIFFERENTIATION between filaments and holdfasts that algae attached itself to rocks with.

Question 21

What are bangiomorpha?

Answer 21

Rhodophytes (red algae)

first evidence of differentiation

Question 22

What are choanoflagellates?

Answer 22

single celled organisms in sponges that create pressure to draw in water. also exist on their own as unicellular or collonial eukaryotes.
Earliest living relative of animals!!
related to bangiomorpha

Question 23

What caused development of Eukaryotes and Metazoans?

Answer 23

Increase in o2 (1%) following huronian glaciation, allowing for development of larger creatures.
- allow diffusion of oxygen if the animal is bigger, need higher atmospheric concentration in order to diffuse

Question 24

Why was the wait so long between developments after the 1st huronian glaciation?

Answer 24

1. Oxygen at 1% was still too low
2. Sulfidic ocean.
   Sulfate reducing bacteria would be present in deep oceans that would produce a lot of sulfate in the ocean, dangerous gas Hydrogen sulfide produced, this would have decreased availbility of metals like molybdenum and copper which are key enzymes in organisms of metabolism.

Question 25

What does H2S do in deep anoxic waters?

Answer 25

HYDRODEN SULFIDE combines with dissolved iron, producing pyrite, explaining by BIF deposition ceased. Pyrite (over magnetite or hematite) precipitated from oceans.
This caused a sulfidic ocean. around 1.84 GA.