Theme 5C

Question 1

What was early earth’s atmosphere like?

Answer 1

It had very little oxygen because it had a reducing atmosphere. Oxidation was prevented by removal of oxygen and other oxidizing gases/vapours (methane, ammonia, dihydrogen). There was basically an input of energy that transformed them into organic compounds instead

Question 2

What was the Urey Miller experiment?

Answer 2

It simulated the early earth conditions and tested the chemical origins of life. 2% of carbon was in amino acid (13 of 22 used in living cells).

Question 3

What did the reducing atmosphere allow prokaryotes to maximize?

Answer 3

ATP production because they had to use a different “food source” (different electron donors)

Question 4

When did the first prokaryotes appear?

Answer 4

Oldest known specimens found 3.2 - 3.4 billion years ago in the Archean. Many are found in stromatolites (cyanobacteria form a biofilm that traps layers of sediment)
- Stromatolites appear 2.7 billion years ago and decline in abundance by 500 million years ago

Question 5

What are cyanobacteria?

Answer 5

Obtain their energy through photosynthesis. Gaseous oxygen is a byproduct of photosynthesis and it converted early earths atmosphere into an oxidizing one (rusting of the earth).

Question 6

How did cyanobacteria affect life on earth?

Answer 6

Dramatically changed the composition of life forms on earth, lead to the near extinction of oxygen intolerant organisms

Question 7

What was the great oxygenation event?

Answer 7

Free oxygen accumulated in the atmosphere via cyanobacteria 2.5 billion years ago, huge increase 850 million years ago.

Question 8

What is the evidence for the great oxygenation event?

Answer 8

• Banded iron formations abundant around that time
• Major changes in number of rock types formed after this event (they were more hydrated and had oxidized minerals)

Question 9

Why was there a long gap before oxygen truly started to take over the atmosphere?

Answer 9

• Long period of anoxygenic photosynthesis
• Free oxygen reacted with ocean chemistry (however when this became saturated it had nowhere to go, hence oxygen in atmosphere)
• Banded iron formations: oxygen reacting with iron and sulfur to form these rocks
• Higher oxygen –> higher carboniferous plants

Question 10

What do eukaryotes have that prokaryotes do not?

Answer 10

Eukaryotes are nucleated and have membrane bound organelles

Question 11

What is the evidence for endosybiosis?

Answer 11

• Membrane bound organelles
• Organelles have their own DNA separate from DNA in nucleus
• mtDNA sequence similar to bacteria/chloroplast sequences in cyanobacteria
• Mitochondria replicate by pinching (binary fission in bacteria)

Question 12

What happened in the paleozoic?

Answer 12

The Cambrian explosion, invasion of land, appearance of larger organisms (like tetrapods)

Question 13

What was the Cambrian explosion?

Answer 13

• Rapid appearance of many groups of organisms 530 million years ago
• Preceded by small shell parts
• Unusually high number of sites with soft body preservation
• Many recognizable features appear: heads, mouths, eyes, legs, etc..

Question 14

Why was there an explosion of life in the Cambrian?

Answer 14

• Increasing oxygen levels from
  eukaryotic algae (allowing higher metabolic rates, bigger body size)
• Reduction of algal mats (new niches opening)
• Shift in ocean chemistry favouring production of calcium carbonate

Question 15

Discuss extinctions.

Answer 15

• Rate of speciation is usually higher than rate of extinction
• Mass extinction is when the rate of extinction exceeds the rate of speciation, they are also periodic (so normal in most cases)

Question 16

Why are mass extinctions important to evolution?

Answer 16

• It allows for ecological niches to be cleared, allowing more opportunities
• Leaves ‘dead clades walking’ (low diversity of once diverse lineages)