The Cambrian time period (named for Cambria - the Latin name for Wales) was the first time period in the Palaeozoic era - the first time period when life existed on the planet. It lasted on average from 541 MYA to 490 MYA.
Nothing yet had lived on land at this time, but in the ocean, it was a different story. Life had already been evolving for millions of years at a slow and steady pace. The seas were full of simply, soft-bodied creatures blindly drifting in the currents. Though, in the coastal shallows below, evolution had stepped onto the accelerator. Predators had taken their first bite.
The Cambrian period was marked by the rise of the sea levels on the planet in the first part of the period, followed by its fall in the second half. By the end of the period, the seas dominated in the northern hemisphere of the planet, the continent of Gondwana - in the south.
When the Cambrian period ended, the Ordovician time period began.