Life creating Oxygen

How did chemisty and oceans produce this?

Remember the two keys to evolution of planetary atmospheres:

Fate of the water vapor (gaseous, liquid, solid)
Fate of the Carbon Dioxide (stays in atmosphere vs. dissolves in liquid water)

After condensation of water vapor produced the earth's oceans, thus sweeping out the carbon dioxide and locking it up into rocks, our atmosphere was mostly nitrogen.

So now let's make some life over the next billion years or so:

A basic definition of Life satisfies the following criteria:

Metabolizes
Derives energy from environment
Reproduces
Evolves, RNA/DNA transfers characteristics

Life requires proteins which come from amino acids, DNA("reference manual") and RNA(builds protein).

Step 1 to Life: Getting Amino Acids

Amino acids are found in meteorites and could have been delivered via impacts (but still what was the process that created them?). But there is also the possibility that AAs were created on Earth. An experiment by Miller and Urey showed that making amino acids is relatively easy given Earth's early conditions, basic molecules of water, ammonia, methane, hydrogen and a spark of electricity (lightning) - but this could only happen in an oxygen-free environment.

Amino Acids now loosely mixed in the oceans

2D view of glycine

3D view of glycine

Most amino acids have a mirror image (L and D)

L and D both found in meteorites
L only in organisms on the earth
why is D selected against?

So now we have some amino acids (monomers) loosely mixed in the oceans. Liquid medium is important:

Protects molecules from UV photon disruption
Ease of transport and Interaction

Next goal is to combine monomers into Polymers (peptide chains) which will become RNA.

Example formation of a peptide chain

To do this, the monomers need to fairly concentrated together to facilitate polymer formation

Step 2: Concentrate the Monomers

Local Evaporation (clays), mud flats Tides?
heat from expelled lava (St. Helens)
tidal pools (bigger tides)
freezing of water

Energy Sources:

lightning
heat
UV

Clays Silicate Surfaces act as a catalyst and may only favor L amino acids

Step 3: DNA/RNA

BIG, Unknown Next Step need to organize a system capable of self-replication (e.g. RNA/DNA)

Organic polymers in high concentration separate out from liquid medium as individual droplets proto-cells
long chain molecules can act as a membrane

EVOLTUIONARY ADVANTAGE: Polymers that could reproduce themselves will survive!

Trial and Error until "right" combination is achieved (DNA)
every living organism on the earth has DNA. Appreciating this complex and amazing process is easy when you can visualize it. Check out the following:

Step 4: First Prokaryotes

1st cells The fossil record indicates that single celled life first emerged 3.5 billion years ago - Prokaryotes which are cells that don't have a nucleus but do have DNA. These early cells ate via fermentation where sugars are consumed and waste products are carbon dioxide and alcohol.

But fermentation is very inefficient, it releases little energy and this becomes a big problem when the food supply is running out

2nd Cells

Anaerobic photosynthesizing bacteria had a huge EVOLTUIONARY ADVANTAGE: Bacteria could process plentiful UV light. After the food supply diminishes, the cells evolved to consume CO₂, H₂S and process UV light via photosynthesis. The waste products were sugars, S₂ (stinky swamp gas) but no oxygen.

Step 5: Cyanobacteria

3rd Cells

Again, the previous cells ran out of food, so new cells evolved to make own food via photosynthesis by developing chlorophyll to efficently absorb UV light:

CO₂ + H₂O + UV light = Sugar + O₂.
Finally! oxygen is the waste product and we have oxygen production. These bacteria are called Cyanobacteria or "blue-green" algae.