Two planets, Venus and Mercury , are closer to the Sun, while the other six are farther away. Earth formed about 4.5 billion years ago, and it is still evolving. Earthquakes and volcanoes are violent proof of Earth's shifting crust. Beneath the mantle is Earth's core, made mostly of nickel and iron. The inner part of the core is solid, but the outer part is liquid.
Oceans cover more than two-thirds of Earth's surface.
The first signs of life on Earth appeared in the oceans about 3.5 billion to 3.9 billion years ago. The first tiny organisms may have been similiar to forms of bacteria living today. The first life on land, simple plants, developed around 430 million years ago. The age of the dinosaurs followed 225 million years later, and human beings evolved less than one million years ago. Above Earth's solid surface lies its atmosphere.