The surface of the earth is very young. In a relatively short period of about 500 million years (according to astronomical standards), erosion and tectonic processes destroyed and reconstructed most of the earth's surface, thus eliminating almost all traces of the early geological surface history (such as impact craters). Therefore, most of the early history of the earth has been erased. The age of the earth is 4.5 to 4.6 billion years, but the oldest known rocks are about 4 billion years old, and there are few rocks over 3 billion years old. The oldest biological fossils are less than 3.9 billion years old. There is no record of the critical period when life first began.

7 1% of the earth's surface is covered with water. The earth is the only planet with water on its surface in liquid form (although there may be liquid ethane or methane on Titan's surface and liquid water on Europa's surface). Of course, as we know, liquid water is essential to life. The heat capacity of the ocean is also very important to keep the earth's temperature relatively stable. Liquid water is also the cause of most erosion and weathering of the earth's continent, which is unique in today's solar system (although it may have happened on Mars in the past).