How did chemisty and oceans produce this?
Properties of Cells Today:
Prokaryotes precede Eukaryotes by approximately 2 billion years.
Making Polymers Today:
4 Billion years ago there were no cells to facilitate this. The available energy sources were
All of the above are quite inefficient compared to enzymes
Now we have a multiplying population of bacteria (prokaryotes) that has to eat to survive:
What to eat?
EVOLUTIONARY ADVANTAGE: Bacteria that could process plentiful UV light
and INorganic molecules will survive
So, chlorophyll evolves to more complex forms so that it can capture and store enough UV energy to breaking the hydrogen-oxygen bond in water.
Now we have a mechanism to deliver Oxygen to the atmosphere via the aerobic photosynthesis of blue-green algae. But, the oxygen does not initially go into the earth's atmosphere. Instead we have to wait 1.5 -2 billion years to get oxygen into our atmosphere!
How did this thing get here?
So now we can crawl out on the Land!
Dispersal of Parental Units by a variety of mechanisms:
Passive: (slowly alters gene pool over time)
Active: (catastrophe "overnight" change in ecosystem)
Survival of the fittest works in well-defined, slowly evolving ecosystems (like the ocean); On long time scales, the role of random catastrophe is more important
Mass extinctions mean:
But in recent years, the number of extinction events and their timescales seems to have grown considerably in complexity. Below are a few examples:
Timescale of extinction is crucial in identifying its cause:
Evidence from Fossil Record: 100-150 million year extinction periodicity ???
Since the orbital period of the Sun around the center of the Galaxy is about 250 million years then every 100-150 million years the earth is in a spiral arm which is a region of high supernova density. It is possible the earth could be subject to high radition from these supernova.
But evidence is pretty startling that impacts are the root cause:
Snowball Earth Hypothesis: