Water is ubiquitous on Earth—about 70% of Earth’s surface is covered by the stuff. Water is in the air, on the surface and inside rocks. Geologic evidence suggests water has been stable on Earth since about 4.3 billion years ago. Water is ubiquitous on Earth—about 70% of Earth’s surface is covered by the stuff. Water is in the air, on the surface and inside rocks. Geologic evidence suggests water has been stable on Earth since about 4.3 billion years ago. Planetary Sciences Phys.org – latest science and technology news stories