In 2007, a piece of oceanic crust found in Greenland was dated by scientists to be around 3.8 billion years old. The age of the oldest oceanic rocks was previously determined to be approximately 200 million years old.
The rocks covering the ocean floor, known as oceanic crust, vary in geologic age and composition from the rocks covering the continents, known as continental crust.
The oldest continental crust was previously dated at 3.8 billion years old. However, new findings confirm that zircon crystals found in Western Australia are 4.4 billion years old.
The oceanic rocks discovered in Greenland are identified as ophiolites, referring to slabs of oceanic crust that were later transported to land in a process called seafloor spreading.