Question

1. explain when and how oxygen first began to accumulate in earths atmosphere according to the video. what biological process led to this change, and roughly where on the field does this occur?

Explanation:

Oxygen first accumulated in Earth's atmosphere around 2.4 - 2.5 billion years ago (the Great Oxidation Event). Cyanobacteria (blue - green algae) performed photosynthesis, a biological process where they used sunlight, carbon dioxide, and water to produce glucose and oxygen ($6CO_2 + 6H_2O \xrightarrow{light} C_6H_{12}O_6 + 6O_2$). Initially, oxygen was absorbed by minerals (like iron in the oceans, forming banded iron formations). Once these "sinks" were saturated, oxygen started to accumulate in the atmosphere. This process occurred in aquatic environments (oceans, shallow seas) where cyanobacteria lived, as they are aquatic organisms.

Answer:

• When: Around 2.4 - 2.5 billion years ago (Great Oxidation Event).
• How: Initially, oxygen produced by cyanobacteria was absorbed by mineral sinks (e.g., iron in oceans). After sinks were saturated, oxygen accumulated in the atmosphere.
• Biological process: Photosynthesis (by cyanobacteria), with the reaction $6CO_2 + 6H_2O \xrightarrow{light} C_6H_{12}O_6 + 6O_2$.
• Where it occurs: Aquatic environments (oceans, shallow seas) where cyanobacteria thrived.