LIFE SCIENCE

Detailed explanation-1: -The rise in oxygen is attributed to photosynthesis by cyanobacteria, which are thought to have evolved as early as 3.5 billion years ago.

Detailed explanation-2: -Cyanobacteria played an important role in the evolution of Early Earth and the biosphere. They are responsible for the oxygenation of the atmosphere and oceans since the Great Oxidation Event around 2.4 Ga, debatably earlier.

Detailed explanation-3: -The release of oxygen by cyanobacteria was thus responsible for changes in the earth’s atmospheric composition, the rise of aerobic metabolism and, ultimately, the evolution of multicellularity. Oxygen is the primary molecule that makes Earth what it is today, far more hospitable and beautiful than the early earth.

Detailed explanation-4: -Some scientists think that 2.4 billion years ago is when organisms called cyanobacteria first evolved, which could perform oxygen-producing (oxygenic) photosynthesis. Other scientist think that cyanobacteria evolved long before 2.4 billion years ago but something prevented oxygen from accumulating in the air.