Let's look at a few general things on this timeline first.
We can see that the Earth's history is broken into three eons: Archean, Proterozoic and Phanerozoic.
Instead of just simple single-celled organisms, multicellular organisms - and even soft-bodied invertebrates like worms, sponges and jellyfish - were found towards the end of the Proterozoic eon.
The Phanerozoic eon covers a small portion of Earth's history, but we have the most information about this eon.
This same idea is used to determine the relative age of rock layers and of the fossils within those rocks.These old life forms were simple but helped to change the atmosphere of early Earth.They helped to produce more oxygen, making the atmosphere more similar to what we have today.Now that we know how scientists determine how old things are - both relatively and more specifically - let's look at a general timeline of the history of life on Earth.We will come back to this image as we discuss specific characteristics and events in each era.