NEET BIOLOGY

Detailed explanation-1: -So how did Earth end up with an atmosphere made up of roughly 21 percent of the stuff? The answer is tiny organisms known as cyanobacteria, or blue-green algae.

Detailed explanation-2: -By around 600 million years ago, concentrations of molecular oxygen in our atmosphere finally reached around 21 percent.

Detailed explanation-3: -Prochlorococcus and other ocean phytoplankton are responsible for 70 percent of Earth’s oxygen production.

Detailed explanation-4: -In fact, the troposphere contains three-quarters of the mass of the entire atmosphere. The air here is 78% nitrogen and 21% oxygen. The last 1% is made of argon, water vapor, and carbon dioxide.

Detailed explanation-5: -"Cyanobacteria are the very first organisms that figured out how to make oxygen. How to take water, which is really abundant everywhere on Earth, and, using sunlight, split its molecules to make oxygen, ” says Bosak.