Photosynthesis is vital for maintaining levels of atmospheric oxygen.

This is true. Photosynthesis plays a vital role in maintaining the levels of oxygen in the atmosphere. Oxygen is a byproduct of photosynthesis

Oxygen is crucial for the survival of most terrestrial and marine animals including man.  The level of oxygen in the atmosphere is about 21%. The process of photosynthesis helps in maintaining this balance. Plants absorb carbon dioxide and produce oxygen.

Without photosynthesis , life on earth would come to a halt. The process of photosynthesis was first discovered, albeit partially, in the 1600s by Jan Baptista van Helmont