The oldest rocks of Saudi Arabia date back to the Precambrian, about 3 billion years ago. They form parts of the Arabian Plate that include the Arabian Peninsula. However, most areas of Saudi Arabia are underlain by the Neoproterozoic rocks (1,000 to 540 million years ago). These younger rocks include those from the Palaeozoic Mesozoic, and Cenozoic Eras, which are collectively called the Rock Cover of the Phanerozoic Eon.