The algae were the inventors of Photosynthesis, and the important part of this is the splitting of H2O into hydrogen and Oxygen. The Hydrogen is used by the plant to help build complex molecules; and the O2 is discharged as a waste gas.

Have a crack at the Siderian period, or the Oxygen catastrophe in Wikipedia.

Algae come in thee colours red, brown and green, and some think all green plants descended from the green Algae.

The Precambrian is the informal time before the Cambrian Period.

It is informally called a Super-Eon and certainly not a geological Era.

Geological time intervals from largest to smallest :-

• Super-Eon - AEonothem (informal)
• Eon - Eonothem
• Era - Erathem
• Period - System
• Epoch - Series
• Age - Stage
• Chron - Chronozone (informal)