The oldest continental rocks are found in cratons. A craton is a stable part of the continental lithosphere, which has survived several cycles responsible for the merge and the dislocation of supercontinents. Cratons are therefore always found within continents. Some cratons in Canada and Greenland shelter the oldest continental rocks in the world, about 4 billion years old. Other cratons in South Africa, Australia and Asia have continental rocks that are 3 billion years old.
The oldest seafloor is comparatively very young, approximately 280 million years old. It is found in the Mediterranean Sea and is a remnant of an ancient ocean that is disappearing between Africa and Europe. The next oldest seafloor is found at the margins of the north Atlantic Ocean and the northwestern Pacific Ocean, as far as possible from the mid-ocean ridges where they were created. These parts of the seafloor are about 200 million years old.
Age of the oceanic crust. Courtesy of NOAA.