Answer:
The correct answer is Oxygen.
Step-by-step explanation:
2.0 BYBP means 2 billion year before present.
The theory of evolution holds that the the synthesis into primitive life forms of the basic chemical components of life such as carbon, nitrogen, hydrogen and oxygen occurred in an atmosphere without any oxygen.
The presence of oxygen in our plant today is explained by two processes.
They are:
- Photosynthesis and
- One is photochemical dissociation. This refers to a reaction between the suns ultraviolet radiation and water molecules in the upper atmosphere. This photochemical reaction is said to have contributed to the oxygen in the plant today.
The process of Photosynthesis which is the chief contributor of oxygen to the earths atmosphere is said to have spanned billions of years.
Cheers!