What Is the Earth Made Of?

Earth whirls its way through space almost 93 million miles away from the sun. As far as we know, it is the only planet that supports life as we understand it. Humans have long organized their lives around the movement of the earth, so we know it revolves on its axis in slightly less than 24 hours and that it completes its path, or orbit, around the sun in approximately 365 days. But what is the Earth made of?

Features

Earth scientists tell us that the term "Earth" includes the planet's atmosphere, its surface,and its interior. Gravity holds Earth's atmosphere in place. The multiple layers of the atmosphere are composed of 79 percent nitrogen, 20 percent oxygen, and 1 percent other gasses. The layer closest to the surface of earth, the troposphere, is where weather as we know it happens.

Geography

The surface of the Earth is made of rock. That's right--beneath the mud, dirt and sand of the continents and the depths of the oceans, you'll find hard rock all the way around. The lithosphere, or crust, is the outermost layer of the earth, extending from 40 to 60 miles deep. The crust is a very thin layer, and it's thinner under the oceans than it is on the continents; ocean crust is volcanic basalt and continental crust is granite, primarily feldspar and quartz.

Identification

The mantle of the Earth, which lies directly under the crust, accounts for most of the planet's mass. It consists of iron, magnesium, aluminum, silicon and oxygen. The mantle is solid, but it is extremely hot (1000 degrees C), so scientists describe it as plastic.

Theories/Speculation

The Earth's core consists of two parts. The inner core is extremely hot, yet the tremendous pressure exerted on it makes it a solid mass of iron. The outer liquid core is made of iron and nickel. Scientists theorize that convection currents in this outer core occasionally cause changes in the Earth's magnetic field. This suggests that "magnetic north" has not always been and may not always be where it is today.

Considerations

The Earth is always changing. Plate tectonic theory tells us that the continents continue to slip and slide across the planet's surface. There are three classes of rocks on Earth: igneous rocks come from molten material below the Earth's crust; sedimentary rocks are laid down in layers as wind and water cause erosion and deposition of minerals; and metamorphic rocks started out in one form and were changed through heat and pressure to something different.