What is the Earth made of? All matter is composed of elemental particles called atoms. Atoms are the smallest building blocks of chemical materials and the different types of atoms are called elements. Atoms are grouped in a multitude of combinations to make molecules. Molecules are the chemicals with which we interact and each molecule has different properties.
The most common element on the planet Earth is oxygen. Oxygen makes up about 20% of the air we breathe but actually constitutes nearly 47% of the planet. Most of the oxygen on Earth is combined with other elements to form substances like water and sand.
The second most common element on our planet is silicon making up almost 28% of the surface of the Earth, or the crust. Silicon combined with oxygen makes up the majority of the crust of the planet. These minerals (a name for a particular type of chemical compound or molecule) are the silicates. Quartz and quartz sand is the most common silicate but when other elements are combined with the silicon and oxygen other minerals are formed. When potassium, calcium or sodium, along with aluminum, are combined with silicon and oxygen a mineral called feldspar is formed. Other elements combined with silicon and oxygen form mica, hornblende and many other minerals.
Aluminum is the third most common element in the Earth's crust. Aluminum combines in silicates to form feldspar, a very common mineral. Aluminum oxide, aluminum combined with oxygen, forms corundum, a very hard substance used to make sandpaper. If corundum is combined with other elements it can form many of the gemstones we are familiar with including ruby, sapphire and topaz. Gemstones are rare minerals that in their purest forms are highly prized for jewelry and other purposes.
On the surface of the planet, at about 5%, iron is the fourth most common element. Deeper in the Earth it is believed that the core, or center, of the planet is mostly iron. Iron combines in a wide number of ways with other elements to form many, many different minerals. From some of these minerals we get pure iron that is then combined with other elements to form the iron and steel materials that we use for tools, construction and many other purposes. Iron is also very important to life as it is a key component that allows blood to carry oxygen throughout our bodies.
After these top four elements the light metals calcium, sodium, potassium and magnesium are the most common elements in the Earth's crust. Totaling together about 15% of the surface of the Earth, these elements make up a number of different minerals. Sodium, combined with chlorine, forms the substance we know as salt. These four elements are also common in many of the silicates. Calcium is used by our bodies to form bones and is used to form the shells of sea creatures.
After these top 8 elements in the Earth's crust, all other elements make up only about 1.5% of the surface of the Earth. These elements include hydrogen, the most abundant element in the universe, and carbon, the basic building block of life as we know it. The second most common element in the universe, helium, is almost non-existent on the Earth. This is because it is so light and doesn't combine with other elements to form compounds. Since there is nothing to hold this element to the planet it escapes through the atmosphere into space relatively quickly. Quickly in terms of the life of the planet, that is.
This discussion of the composition of the Earth's crust isn't the whole story about what the Earth is made of. The crust makes up only about 5% of the entire planet. When the depths of the Earth are considered iron and nickel become some of the very most common elements on the planet. In the oceans hydrogen, in the form of water, is prevalent. And, in the atmosphere, nitrogen is the most common element.
Further understanding of why the planet is made up of these materials involves fascinating knowledge of chemistry and geology. I would encourage you to study further to more fully grasp the beauty of the processes that have formed our planet and our universe.