Cambrian

The Cambrian is the first geological period of the Paleozoic. It lasted from 541 to 485.4 million years ago.

Geography
It is still debated how exactly the continents were positioned in the Cambrian. Sea levels were high (as a result of the melting ice from Snowball Earth), and land was concentrated in the Southern Hemisphere.

Climate
All we know is that it was rather warm.

Plants
Plants had not evolved in the Cambrian, but it is possible that fungus and algae existed.

Animals
The Cambrian was the time of the Cambrian Explosion, when animals evolved very rapidly from jelly-like blobs into hard-shelled, some predatory creatures. Well-preserved examples of these can be found in the Burgess Shale of western Canada. This was the golden age of the trilobites; after the Cambrian they slowly declined as bigger, better predators evolved.