My Science School

What is inside the Earth?

The Earth is not solid rock all the way through. It has an inner core of solid rock, which is mostly iron. The temperature here is probably around 4,500°C. Beyond the inner core is a layer of liquid rock, called the outer core, which extends about halfway to the surface. Beyond this is a thick layer of rock called the mantle, which is partly molten and runny. The thinnest layer, or crust, is on the Earth’s surface, floating on the red-hot liquid mantle. The crust is about 6 km thick under the oceans, but 30 to 40 km thick beneath the land. 

Why is the Earth like a magnet?

The Earth acts as if it is a huge magnet. When the solid rocky core moves inside the liquid rock above it, it creates a magnetic field with a north pole and a south pole. This field surrounds the Earth and extends right out into space. The Earth’s magnetic field is changing constantly. This means that the magnetic north pole is not always the same as the geographic, or true, North Pole that you find on a map, although it wanders about in the same region. Millions of years ago, the north magnetic pole lay in what is now the Sahara desert. 

How old is our Earth?

The Earth is thought to be about 4,600 million years old. The oldest rocks so far discovered are up to 3,800 million years old. The Universe is much older, and probably began about 15,000 million years ago. We can calculate the ages of the Earth and the Universe by examining meteorites, and also by looking at changes in the atomic structure of some of the elements found on the Earth. Radioactive elements decay at a steady rate, and these changes can indicate the age of the Earth and other planets, as well as the age of the stars.