The history of life on earth Early EarthThe earth is 4.5 billion years old. The earth's early atmosphere contained no oxygen. Methane

AmmoniaHydrogen

3.8 billion years ago, the earliest form of life appeared on earth.Cyanobacteria are single-celled algae that are photosynthetic.

Over hundreds of millions of years, cyanobacteria released oxygen into the atmosphere. - ozone- oxygen-breathing organisms

Invertebrates (simple animals without backbones) started to appear:- worms- jellies- corals

Then 544 million years ago, organisms with shells started to appear.

The first animals with backbones evolved. They lived in the ocean.

Ferns and mosses

Amphibians and reptiles start to appear

Early birds

Very small mammalsPlants evolved to be more complex -> gymnosperms

Small primateshominids

Angiosperms are the most complex of all plants Humans are the most complex

and intelligent of all animals

Write a 1 paragraph summary about how life came to be on earth.