What is the Earth Made of?
The third planet from the Sun, Earth, contains large amounts of water. Other planetary bodies in the Solar System contain large quantities of water as well, but Earth has no other known astronomical object that supports liquid surface waters. The oceans cover 71% of Earth’s surface, dwarfing its rivers, lakes, and polar ice. It is the only planet known to have life, making it particularly interesting and important. For more information, read our introduction to the ocean.
The earth is made up of four main components: the outer core, the mantle, and the inner core. Each layer is composed of different materials and has different physical and chemical states, and their properties influence the life on the surface of the planet. Variations in the heat in the core cause movement in the mantle, causing earthquakes and other natural hazards. It’s no wonder that Earth has so many layers and is so fragile!
The Earth’s crust is like a hard boiled egg shell. It is very thin and cold, and is composed primarily of relatively light elements like silica, oxygen, and aluminum. In some places, the Earth’s crust is as thin as 5 km, even under the oceans. In some places, it can be as thick as 70 km. For comparison, the outermost layer of the Moon is around 70 miles thick. The crust is the largest part of Earth, and is made up of mostly water.
The surface of the Earth is flat and rounded. In other places, water is irregular and has variations in elevation. The oceans’ geologic layers are analogous to land, and the differences between the two are often referred to as topography. Aside from the topography of land, the sea surface topography is an example of what makes the earth beautiful and unique. Its differences from the mean sea level are characterized by their geological layers.
Aside from the Earth’s surface, the interior of the Earth is also incredibly fascinating. Though the Earth’s surface is just a scrape, it is still a huge, complex planet. It is 6,400 kilometers deep, and it has four layers. The deepest layer, the crust, has never been explored by humans. The deepest human-made hole is twelve kilometers (7.6 miles), and it took 20 years for scientists to reach the bottom.
The interior of the Earth consists of three layers. Its core is 30 kilometers below the surface, while its mantle is 1,800 kilometers below. It is made of iron, magnesium, and silicon, and is dense and semi-solid. The mantle is very hot, and its temperature is high enough to melt rock, forming partially melted rock. The mantle is also where the Earth’s tectonic plates slide, causing them to tilt and collide.