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Common Elements

Earth Elements, Water Elements, Air Elements, Elements of Life, Elements in Space

There are ninety-two elements found on Earth. But only a few are very common. Most elements are found only in small quantities.

Sorting the Elements Oxygen and silicon are the most common elements in the ground. This is because many rocks are made mainly of a substance called silicon dioxide. This substance is a combination of silicon and oxygen.

Earth Elements

The ground beneath our feet is made mostly from just eight elements. They are oxygen, silicon, aluminum, iron, calcium, sodium, potassium, and magnesium. Many rocks are made from a mix of silicon and oxygen. Rocks such as chalk are mostly calcium and oxygen. Metals such as iron and aluminum are found in rocks called ores. The Earth's core is mostly iron.

Water Elements

The main elements in the ocean are hydrogen and oxygen. These are the elements that make water. Sodium and chlorine are found in small amounts in seawater. They make the sea salty. Other elements are found in small amounts, too. These include sulfur, magnesium, calcium, and potassium.

Sorting the Elements The 92 elements found on Earth combine together in different ways. They make up the air in the atmosphere, the water in the sea, and the rocks beneath us.

Air Elements

Air is nearly 99 percent nitrogen and oxygen. Another 1 percent is argon. There are also small amounts of other gases in it. Carbon dioxide is one of them.

Sorting the Elements


Magnesium is important to all life. How? All living things depend on plants. Plants can make their own food from sunlight. The green color in plants is chlorophyll. This is the main substance for absorbing light. Magnesium is an essential part of chlorophyll.

Elements of Life

All living things are made up of just a few elements. For example, all living things have a great deal of water. Oxygen and hydrogen make water. So they are important elements. Other important elements include carbon and nitrogen. Animals and plants also need small amounts of several other elements. Two of these are calcium and iron. In humans, calcium is an important element for teeth and bones. And iron is needed for the blood.

Sorting the Elements 94 percent of the human body is made up of the key elements oxygen, carbon, and hydrogen.

Elements in Space

On Earth, oxygen is the most common element. Beyond Earth the most common element is hydrogen. More than 92 percent of the universe is hydrogen. Most of the rest is helium. Other elements make up only about one ten-thousandth of the universe.

Hydrogen is also found in stars. Stars are huge balls of it. This is the fuel that keeps them burning. Also, huge clouds of hydrogen gas float in space.

Sorting the Elements Our Sun is just one of billions and billions of stars in the universe. Every one of these stars is made mostly of the element hydrogen.


Stars burn hydrogen. It is converted into elements such as carbon, oxygen, nitrogen, and iron. A few giant stars make elements that are heavier than iron. The heaviest elements, such as gold and uranium, are made in explosions called supernovas. These happen when a large star comes to the end of its life.

Sorting the Elements This photo of the Orion nebula shows reddish clouds of hydrogen.

The fourteen most common elements in the universe
1 hydrogen 10,000,000
2 helium 1,400,000
3 oxygen 6,800
4 carbon 3,000
5 neon 2,800
6 nitrogen 910
7 magnesium 290
8 silicon 250
9 sulfur 95
10 iron 80
11 argon 42
12 aluminum 19
13 sodium 17
14 calcium 17
all other elements 50

The table shows the number of atoms of each element per 10 million hydrogen atoms.

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Science Encyclopedia for KidsSorting the Elements