Surface and Interior of Earth

Click on image for full size version (378K GIF) Image courtesy of NASA

Earth, the largest and densest rocky planet, was formed about 4.5 billion years ago. The Earth's interior is divided into four layers, which is typical of rocky planets. Each layer has different characteristics and is made of different elements and minerals.

There are many different types of features on Earth’s surface due to the complexity of our planet. The surface is unique from the other planets because it is the only one which has liquid water in such large quantities. Water forms some features of Earth's surface such as rivers, oceans, beaches and lakes. Other surface features, such as mountains, earthquakes and volcanoes, are formed when large pieces of the Earth’s outer layer move slowly by plate tectonics.

Structure of the Interior of Earth

Click on image for full size version (64K GIF)

Earth has a diameter of 12,756 km (7,972 mi). The Earth's interior consists of rock and metal. It is made up of four main layers:
1) the inner core: a solid metal core made up of nickel and iron (1200 km diameter)
2) the outer core: a liquid molten core of nickel and iron
3) the mantle: dense and mostly solid silicate rock
4) the crust: thin silicate rock material

The temperature in the core is hotter than the Sun's surface. This intense heat from the inner core causes material in the outer core and mantle to move around.

The movement of material deep within the Earth may cause large plates made of the crust and upper mantle to move slowly over the Earth’s surface. It is also possible that the movements generate the Earth's magnetic field, called the magnetosphere.

Surface of the Earth

Click on image for full size version (383K GIF) Image from: Rick Kohrs, Space Science and Engineering Center, University of Wisconsin, Madison

Most of the Earth's surface (70%) is covered with water, and the remaining 30% is taken up by the seven continental landmasses. However, underneath the water that fills the oceans, and the dirt and plants that cover the continents, the Earth’s surface layer is made of rock. This outer layer formed a hard, rocky crust as lava at the surface cooled 4.5 billion years ago.

The crust is broken into many large plates that move slowly relative to each other. Mountain ranges form when two plates collide and their edges are forced up. In addition, many other surface features are the result of the moving plates. The plates move about one inch per year, so millions of years ago the continents and the oceans were in different positions. About 250 million years ago, most of the land was connected together, and ov

This image shows the divisions of the Earth's interior. Click on the image to see labels. (Adapted from Beatty, 1990)

er time has separated into seven continents.