By mass:

* Iron (Fe): About 32.1%

* Oxygen (O): About 30.1%

* Silicon (Si): About 15.1%

* Magnesium (Mg): About 13.0%

* Sulfur (S): About 2.9%

* Nickel (Ni): About 2.4%

* Calcium (Ca): About 1.5%

* Aluminum (Al): About 1.4%

By volume:

* Iron (Fe): About 32.1%

* Oxygen (O): About 29.5%

* Silicon (Si): About 15.0%

* Magnesium (Mg): About 12.9%

* Sulfur (S): About 2.8%

* Nickel (Ni): About 2.3%

* Calcium (Ca): About 1.4%

* Aluminum (Al): About 1.3%

Important Note: This composition primarily refers to the entire Earth, including the core, mantle, and crust. The proportions are very different when considering the Earth's crust alone:

* Oxygen (O): About 46.6%

* Silicon (Si): About 27.7%

* Aluminum (Al): About 8.1%

* Iron (Fe): About 5.0%

* Calcium (Ca): About 3.6%

* Sodium (Na): About 2.8%

* Potassium (K): About 2.6%

* Magnesium (Mg): About 2.1%

These elements are combined to form various minerals and rocks.