What was the amount of oxygen in earths early atmosphere

Answer: 21%

Explanation:

The atmosphere is the gaseous portion of the planet Earth. It therefore consists of several gases and air particles.

In the atmosphere,

-Nitrogen is the most abundant gas with 78%

- Oxygen takes 21%,

- Carbon dioxide takes 0.03%,

- the remainder is unreactive gases and particles.

The amount of oxygen in earths atmosphere was about one ten-quadrillionth of the of the amount presented today