EVOLUTION OF LIFE

At present, Earth provides the only example of an environment that has led to the evolution of life. It is believed that high energy chemical processes produced a self-replicating molecule around 4 billion years ago, and between 3500 and 3.8 billion years ago the last common ancestor existed universal. the development of photosynthesis allowed the living recogiesen energy directly from the Sun; the resulting oxygen accumulated in the atmosphere ozone layer formed (a form of molecular oxygen [O3]) in the upper atmosphere. The incorporation of smaller within larger cells resulted in the development of complex cells called eucariotas.43 True multicellular organisms formed as cells within colonies became increasingly specialized. Life colonized the surface of Earth in part by the absorption of ultraviolet radiation by the layer ozono.

In the 1960s a hypothesis which states that during the Neoproterozoic period, from 750 to 580 Ma, there was intense glaciation in which much of the planet was covered by an ice sheet emerged. This hypothesis has been termed the "global glaciation", and is of particular interest since this event preceded the so-called Cambrian explosion in which multicellular life forms began to proliferar.