AP BIOLOGY

Detailed explanation-1: -Description: The Great Oxygenation Event occurred when cyanobacteria living in the oceans started producing oxygen through photosynthesis. As oxygen built up in the atmosphere anaerobic bacteria were killed leading to the Earth’s first mass extinction.

Detailed explanation-2: -The permanent introduction of oxygen into the atmosphere fundamentally changed the ecology of the planet. The first impact was on anaerobic organisms, which didn’t need oxygen to survive. The rise in oxygen levels was poisonous to them and led to most them becoming extinct.

Detailed explanation-3: -A global depletion of oxygen caused the planet’s first mass extinction about 550 million years ago, an event that killed 80% of the animals in existence at the time, according to a new study by geobiologists at Virginia Polytechnic Institute and State University, also known as Virginia Tech.

Detailed explanation-4: -Scientists think that algae first evolved approximately 2.7 billion years ago, and soon after this oxygen began to exist in the atmosphere. Photosynthesis by primitive plants and algae released oxygen, which gradually built up in the atmosphere.

Detailed explanation-5: -Since its first appearance 2.33 billion years ago, oxygen accumulated in high enough concentrations to have a weathering effect on rocks just 10 million years later. This weathering process, however, would have leached more sulfate and certain metals into waterways and ultimately, the oceans.