Evolution and Systematics

Question 1

When was the earth formed? how is this possible to know?

Answer 1

4.53 to 4.58 billion years ago, based on slowly decaying radioactive isotopes

Question 2

When did water come and how?

Answer 2

4.3 billion years ago, asteroids/meteors

Question 3

Describe the evidence that microbial life existed early in earth’s history.

Answer 3

microfossils

Question 4

How was the atmosphere on earth before life existed?

Answer 4

The atmosphere contained no oxygen

• Water, methane, carbon dioxide, nitrogen and ammonia

Question 5

Experiments show that biomolecules can form spontaneously, describe these experiments.

Answer 5

If the gases that existed is radiated with UV or exposed for electrical discharges →
biochemical building blocks
• These can, through polymerization, form important macromolecules

Question 6

How and where was life formed - the current hypothesis.

Answer 6

One hypothesis is that life may have originated well below Earth’s surface on hypothermal springs on
the ocean floor
• Less hostile and more stable conditions than on the Earth’s surface
• Firm supply of energy in form of reduced inorganic compounds, e.g. H2 and H2

Question 7

How did the first cells look like?

Answer 7

primitive prokaryotic like

Question 8

Why did DNA-based cells arise?

Answer 8

DNA is more stable, RNA is susceptible to hydrolysis

Question 9

What happened when the cyanobacteria evolved approximately 2.8 billion years ago?

Answer 9

Oxygen → Iron-oxides, i.e. atmosphere was not altered
Great oxidation event
• Happened 2.4 billion years ago
• Anoxic to oxic atmosphere
o O2 accumulation in atmosphere (required by aerobic organisms)
o O3 accumulation
(protection against UV)
Aerobic/anaerobic organisms could start evolving