What Makes Earth?

The most common elements and compounds on Earth

The earth is a wonderful planet capable of sustaining human life. But what actually makes up Earth? What makes up the air we breathe and the ground we walk on? 

Elements in the Atmosphere

The air is a key component that makes life possible on Earth. These are some of the most common elements in the atmosphere:

Nitrogen: Nitrogen (N2) makes up 78% of our atmosphere (2). It is important to life because it’s found in an amine group within all amino acids. Unfortunately, the gaseous form of N2 found in the atmosphere isn’t directly usable by plants. Instead, it needs to be fixated into other compounds like ammonia (NH₃) and ammonium (NH₄+) by organisms like bacteria and blue-green algae which move the nitrogen into other compounds in the soil. Interestingly, nitrogen can also be fixated by lightning (3).

Oxygen: Oxygen (O2) makes up 22% of our atmosphere and is an essential part of life (2). Humans breathe O2 into their lungs and use it for cellular respiration, a process necessary for survival. Notably, because insects absorb O₂ through their exoskeleton, in prehistoric times when oxygen levels were over 30 percent, insects would rule the skies, and had wingspans of up to 28 inches in length (4). Oxygen also forms O3, or ozone, an important part of our stratosphere that helps absorb UV light and protect Earth from harmful radiation (2). 

Argon: Argon is the third most abundant element in our atmosphere at about 0.94% (2). Although not as important to human life, this stable noble gas is used in welding to ensure metals don’t oxidize. Its stability is used in fluorescent and low energy lights to allow electric discharge. Argon exists as a result of decaying potassium (5).

Argon discharge tube

Greenhouse gasses: Greenhouse gasses stop heat from leaving the earth’s atmosphere. Greenhouse gasses include well-known molecules like carbon dioxide (CO2) and methane (CH4), but also water vapor. Water vapor is the most abundant greenhouse gas, but it always changes as water evaporates and rain falls.

Elements of the Earth’s Crust

The crust is the 1% of the earth right below the surface (6). These are some of the most common elements in this reachable underground:

Oxygen: 43% of the crust is oxygen. Most molecules in the crust are metals bonded to oxygen. Typically, oxygen pairs with silicon, aluminum, iron, or even carbon and calcium. The products of such bonding can be compounds like rust and limestone (1). Of course, this includes water (H₂O), which makes up for 60-70% of the human body (6).

Silicon: Silicon makes up 28.2% of the crust (1). It most commonly combines with oxygen to form Silicon dioxide, which is most abundant in the crust. Silicon dioxide (SiO₂) is found in rocks like quartz, opal, and amethyst in the crust. Additionally, different mixes of SiO₂ among other substances make different sand types. In high concentrations, they make for silica sand, which has a variety of uses in water filtration, glassmaking, and ceramics (7).

Beaches are a place where sand containing silicon dioxide(SiO₂) and water can be found.

Aluminum: Aluminum is the first heavy metal in the periodic table, and the most abundant metal in the crust. Like silicon, it’s often found with oxygen in the form aluminum oxide (Al₂O₃), which is around 7% of the crust (8). Aluminum is often used for kitchen foil, but its light weight also makes it helpful in building rockets (8).

Iron and Nickel: Iron and nickel are more common deeper in the earth. They are abundant in the deepest regions of Earth: the mantle and the core. Still, iron makes for the fourth most abundant element in the crust (9). It is one of the most commonly mined metals, and moved civilization into the Iron Age. It has since been a staple part of buildings in the form of steel (6).


  1. Venditti, B. (2021, December 4). Visualizing the abundance of elements in the Earth’s crust. World Economic Forum. Retrieved October 9, 2022, from https://www.weforum.org/agenda/2021/12/abundance-elements-earth-crust/
  2. What’s in the Air? Center for Science Education. (n.d.). Retrieved October 9, 2022, from https://scied.ucar.edu/learning-zone/air-quality/whats-in-the-air#:~:text=The%20most%20abundant%20naturally%20occurring,most%20abundant%20gas%20at%200.93%25.
  3. Britannica, T. Editors of Encyclopedia (2021, July 24). Nitrogen Cycle. Encyclopedia Britannica. Retrieved October 9, 2022 from https://www.britannica.com/science/nitrogen-cycle
  4. Stephens, T. (2012). Reign of the giant insects ended with the evolution of birds. UC Santa Cruz News. Retrieved October 21, 2022, from https://news.ucsc.edu/2012/06/giant-insects.html 
  5. Royal Society of Chemistry. (2017). Argon. Periodic Table. Retrieved October 9, 2022, from https://www.rsc.org/periodic-table/element/18/argon 
  6. Dodd, C. (2020, November 5). The most abundant elements in the Earth’s crust. WorldAtlas. Retrieved October 9, 2022, from https://www.worldatlas.com/articles/the-most-abundant-elements-in-the-earth-s-crust.html 
  7. What is Silica Sand & How is it different from regular sand? Shaw Resources. (n.d.). Retrieved October 19, 2022, from https://shawresources.ca/what-is-silica-sand/ 
  8. Thomas Jefferson National Accelerator Facility- Office of Science Education. (October 9, 2022). 10 Most Abundant Compounds in the Earth’s Crust. JLab Science Education. Retrieved October 9, 2022, from https://education.jlab.org/glossary/abund_com.html
  9. Evers, J. (Ed.). (2022, August 9). Mantle. National Geographic. Retrieved October 9, 2022, from https://education.nationalgeographic.org/resource/mantle