During the first 500–600 million years of the Earth's history, the crust was continuously destroyed by convection within the very hot young planet and by meteorite bombardment. This turbulent period is known as the Hadean Era, which is defined as the period from which no geological record exists (no rocks were preserved). The oldest rocks known on the Earth occur in Canada and West Greenland and appeared between 4000 and 3800 million years ago (Ma). They define the beginning of the Archean Era, which gave way to the Proterozoic (“earlier life”) Era 2500 Ma. Until recently, no fossils were known from the Archean.