Oxygen, the most abundant element in the Earth's crust, makes up about what percentage of the crust by weight?

Oxygen is the most abundant element in the Earth's crust, making up about 46.6 percent of it by weight. It is found combined with other elements, mainly in silicate minerals and oxides.

Abundance of elements in the Earth's crust (by weight, approximate):

• Oxygen: 46.6 percent
• Silicon: 27.7 percent
• These two are followed by several metals, and eight elements together make up about 98.5 percent of the crust.

Why oxygen is so abundant in the crust:

• Oxygen combines easily with other elements.
• Most rocks are made of silicate minerals, in which silicon and oxygen form the basic building block, the silicon-oxygen tetrahedron.
• Quartz, the common mineral in sand, is silicon dioxide.

Oxygen in other parts of the Earth:

• In the atmosphere, oxygen makes up about 21 percent by volume, after nitrogen (about 78 percent).
• In water, oxygen makes up about 89 percent by weight, since a water molecule has one oxygen atom and two hydrogen atoms.
• In the human body, oxygen is the most abundant element by weight, about 65 percent, mainly because of water.

Composition of the whole Earth:

For the Earth as a whole, the most abundant element by mass is iron (about 32 percent), followed by oxygen (about 30 percent), silicon and magnesium.

Composition of the universe:

In the universe as a whole, hydrogen is the most abundant element, followed by helium.

Silicon:

Silicon, the second most abundant element in the crust, is the basis of the semiconductor industry.

Why not the other options?

• ✗27.7 percent is the share of silicon in the crust.
• ✗21 percent is the share of oxygen in the atmosphere by volume.
• ✗78 percent is the share of nitrogen in the atmosphere.