Where does life come from?

Why is Earth able to sustain such advanced forms of life?

The critical step for the evolution of life was the appearance of nucleic acids. Nucleic acids are able to reproduce and serve as templates for larger, more complex molecules. They are present in all living cells and are the over name for RNA and DNA.

Along with nucleic acids appeared amino acids. These molecules are the building blocks for proteins.

The next step was the enclosure of proteins and other biological molecules by membranes. fatty acids are molecules that do not dissolve in water, rather they form a membranous films. When agitated these films form vesicles which encloses internal molecules.

For around two billion years, most organisms only consisted of one cell, these organisms known as prokaryotes were confined to the oceans since early Earth was exposed to damaging amounts of ultraviolet rays and there was little to no oxygen.

Then, around 2.7 billion years ago the first signs of photosynthesis began to appear. The earliest photosyntheic cells were prokaryotic organisms. Over time these organisms became so vast that the oxygen they released began to accumulate in the atmosphere. Oxygen in the atmosphere allowed life to move on to land.

Prokaryotic cells do not contain a nucleus or any other membrane bound organelles such as the mitochondria and chloroplasts. Organelles function similarly as organs in the human body. Over time eukaryotic cells developed out of the previous prokaryotic cells. These cells contain a nucleus and other membrane bound organelle.

Eukaryotes developed from Prokaryotes through the process of endosymbiosis where a larger prokaryotic cell engulfed a smaller cell. Instead of digesting it, the smaller prokaryotic cell, over time, became part of the larger one. This theory is what most researchers believe was the beginning of eukaryotic cells and thus the start of the evolution of complex forms of life.