The presence of life in its present form would not be possible if the earliest life forms had not changed constantly, adapting to their environment and circumstances. Getting from the far left in figure 6 to the far right, where humans appeared, involved billions and billions of tiny changes, starting with the first cell that appeared about a billion years after the planet itself was formed.
- Two types of prokaryotic cells were present when life began and are still around today: Archaebacteria and bacteria. (Single celled)
- Prokaryotic cells increased in complexity over the time
- Eukaryotic cells first appeared approximately 1.5 billion years ago. Development of the green pigment chlorophyll enabled the use sunlight energy to make food from water and carbon dioxide, releasing oxygen into the Earth’s atmosphere for the first time.
- These, the first plants gave rise to the Plant Kingdom we know today. They not only maintain an oxygen rich atmosphere, but make the food upon which all other life depends.