We know that the atmosphere became more oxygen-rich around 1.8 billion years ago (ga) because of geologic evidence such as choose one:

a. redbeds that formed after 1.8 ga.

b. abundant fossils of land plants, signifying the start of photosynthesis.

c. bifs that occurred prior to 1.8 ga but disappeared from the rock record after that time.

d. the presence of abundant pyrite after 1.8 ga.

A. redbeds that formed after 1.8 Ga.

Explanation:

Red beds are known to be as the rocks which are sedimentary which are red in colour and contain high amount of ferric oxides.

good thing- during decomposition the organic molecules in organic matter are broken down into simpler organic molecules that require further decomposition or into mineralised nutrients

bad thing- it can be harmful in crop productivity