4100 million years
or 1000 meters to today
Geological era: Archean
Biological evolution replaces chemical evolution 500 million years after Earth is formed. This marks the beginning of the development of life. Life appears at first in water, and spreads out from there. Proto-cells begin to multiply. They pass their most successful traits on to their descendants. Sometimes new changes appear, and these are subject to natural selection.
As you continue walking, try to imagine how incredibly long 4100 million years is.
The first atmosphere consisted of 80% water vapour and 10% carbon dioxide and sulphur dioxide, nitrogen and other small molecules (hydrogen, sulphur oxide, carbon monoxide, methane and ammonia). Cooling caused the water vapour to condense, resulting in continuous rain and the forming of the oceans.