We need natural resources for just about everything we do. We need them for food and clothing, for building materials and energy. We even need them to have fun. Table 2.1 gives examples of how we use natural resources. Can you think of other ways we use natural resources? Use Vehicles Resources Rubber for tires from rubber trees Steel frames and other metal parts from minerals such as iron Example iron ore Electronics Plastic cases from petroleum prod- ucts Glass screens from minerals such as lead lead ore Use Homes Resources Nails from minerals such as iron Timber from trees Example spruce timber Jewelry Gemstones such as diamonds Minerals such as silver silver ore Food Sunlight, water, and soil Minerals such as phosphorus corn seeds in soil Clothing Wool from sheep Cotton from cotton plants cotton plants Recreation Water for boating and swimming Forests for hiking and camping pine forest Some natural resources are renewable. Others are not. It depends, in part, on how we use them.

Are natural resources renewable?

Earths magnetic field helps protect Earth and its organisms. It protects us from harmful particles given off by the sun. Most of the particles are attracted to the north and south magnetic poles. This is where Earths magnetic field is strongest. This is also where relatively few organisms live. Another benefit of Earths magnetic field is its use for navigation. People use compasses to detect Earths magnetic north pole. Knowing this helps them tell direction. Many animals have natural 'compasses' that work just as well. Birds like the garden warbler in Figure 1.36 use Earths magnetic field. They use it to guide their annual migrations. Recent research suggests that warblers and other migrating birds have structures in their eyes. These structures let them see Earths magnetic field as a visual pattern.

How does Earth's magnetic field help humans?

The idea that Earth is a magnet is far from new. It was first proposed in 1600 by a British physician named William Gilbert. Knowing it acts like a magnet is one thing. Knowing why it acts like a magnet is more difficult. In fact, finding out why is a fairly recent discovery. To find out why required new technology. It was the seismograph that made it possible to learn why the Earth acted like a magnet. Seismograph are used to study earthquakes. By studying earthquake waves they were able to learn about Earths interior. They discovered that Earth has an inner and outer core. The outer core consists of liquid metals, mainly iron and nickel. Scientists think that Earths magnetic field is generated here. It is caused by the motion of this liquid metal. The liquid metal moves as Earth spins on its axis.
Why was William Gilbert unable to explain prove theory that the Earth acts like a magnet in 1600?