Question

main source of air in the earth?

Answer 1

trees are the main source

Answer 2

Oceans are the main  source for oxygen on earth atmosphere.

About half of the sources of  oxygen comes from ocean.

The oxygen in ocean are generated by a type of floating plants named as phytoplankton.

Majority of oxygen sources is this plant.

These are tiny oceanic plants.

They are found to float near the water's surface and drift by means of oceanic current.

Phytoplankton produce oxygen by a reaction called photosynthesis.

Phytoplankton are a kind of  microscopic marine algae.

Phytoplankton is the base of several aquatic food resources for whales, shrimp, snails, and jellyfish and many more.