Cyanobacteria
Anvilcloud pointed out that cyanobacteria (blue-green algae) were crucial in developing Earth’s atmosphere into one which would support human life. I was intrigued by that so investigated. It's straightforward but far from simple.
Cyanobacteria exist anywhere where light and moisture are found, from salty oceans to freshwater lakes, hot deserts and cold soils. In symbiosis with plants and algae they provide nitrogen to their hosts.
Three billion years ago there was little oxygen in the atmosphere. Cyanobacteria in the oceans used energy from the sun to split water molecules and produce oxygen. During millions of years, the level of oxygen in the atmosphere rose to a point where it could support life. This process is referred to as the Great Oxidation Event and allowed the evolution of animals and eventually human beings.
Cyanobacteria created the ozone layer, a protective barrier against the sun’s harmful ultraviolet rays.
Scientists continue to study cyanobacteria.
