Earth is our home planet, the only place in the universe where we know for certain that life exists. Earth formed over 4.6 billion years ago from a swirling cloud of gas and dust that gave rise to our entire solar system, including our star, the sun. Scientists hypothesize that this gas and dust collapsed into a disk, with different parts of the disk coalescing into each of the planets in the solar system.
Where is Earth located?
Our planet sits in a small corner of the Milky Way galaxy, 25,000 light-years from the galactic center, according to NASA (opens in new tab). The solar system is situated on a minor arm called the Orion Spur, which branches off from the Sagittarius Arm, one of the galaxy's two major spiral arms.
Earth's circumference is 24,901 miles (40,075 kilometers), making it the largest rocky planet in the solar system, according to Live Science sister site Space.com (opens in new tab). Our planet orbits 93 million miles (opens in new tab) (150,000 km) away from the sun, giving it the right temperature for persistent liquid water on the surface; it's the only known body to orbit in this so-called Goldilocks zone.
What is Earth made of?
Earth is composed of many elements, chief among them oxygen, silicon, magnesium, iron, aluminum and nickel, according to Caltech's Infrared Processing and Analysis Center (opens in new tab). Our planet's crust is a thin outer layer, containing mostly silicate and basaltic rocks, that extends on average around 18 miles (30 km) below the planet's surface, according to the U.S. Geological Survey (opens in new tab) (USGS). The mantle is the next layer down, extending to about 1,800 miles (2,900 km) below Earth's surface. A common misconception is that all the rock in the mantle is melted into magma; in reality, most of it is in a highly viscous form that is so thick that it takes millions of years for its movement to become apparent. In Earth's center is a nickel-iron core that is liquid on the outside, down to 1,400 miles (2,250 km), but is crushed by incredible pressures into a solid form at the lowest depths, according to the USGS.
Earth has several enormous landforms. The largest continent, which is sometimes known as Afro-Eurasia (though more commonly broken up into Africa, Europe and Asia), has a total area of 32.8 million square miles (84.95 million square km), according to the Encyclopedia of World Geography (opens in new tab). North and South America together constitute 16.43 million square miles (42.55 million square km), according to the online encyclopedia Nations Online (opens in new tab), while the frozen continent of Antarctica is 5.41 million square miles (14 million square km). The area of Australia is 2.97 million square miles (7.66 million square km), according to the Australian government (opens in new tab).
Processes below Earth's crust cause these continents to move around over geological time periods. Geologists have discovered underground continents buried deep below the surface, and though nobody quite knows how or when they formed, they may be as old as Earth itself.
What is Earth's atmosphere made of?
Our planet's atmosphere is 78% nitrogen, 20% oxygen, 0.9% argon and 0.04% carbon dioxide, plus trace amounts of other gases, according to NASA. Most human activity takes place in the lowest atmospheric layer, the troposphere, which extends 5 to 9 miles (8 to 14.5 km) over our heads, NASA says (opens in new tab). Above that is the stratosphere, where clouds and weather balloons fly, going up to 31 miles (50 km). This is followed by the mesosphere, which extends up to 53 miles (85 km) in altitude (this is where meteors burn up), and the thermosphere, which reaches far into space, at least 373 miles (600 km) high.
Human activity has a huge effect on climate and weather in Earth's atmosphere. By adding excess carbon dioxide, which traps infrared radiation from the sun, human industry is heating up our planet via global warming. In 2021, the United Nations announced that parts of the Arctic had reached a new temperature record in June 2020: 100 F (38 C) in the Siberian town of Verkhoyansk.
What are some characteristics of Earth?
Earth is tilted on its axis by 23.4 degrees, meaning that sunlight falls unevenly on the planet's surface over the course of the year, creating seasonal variation over most of the planet. But regions experience different variances in sunlight, so Earth's surface is often broken up into three major climatic zones: the polar regions in the Arctic and Antarctic, which start above or below 66 degrees latitude north or south; the middle temperate zones, between 23 and 66 degrees latitude north or south; and the tropical regions, between the Tropic of Cancer, at 23 degrees latitude north, and the Tropic of Capricorn, at 23 degrees latitude south, according to the National Oceanic and Atmospheric Administration (opens in new tab).
The tallest point above sea level is the peak of Mount Everest, at 29,032 feet (8,849 meters), according to Britannica (opens in new tab)). A crescent-shaped trough at the bottom of the western Pacific Ocean known as the Mariana Trench is the deepest spot on our planet, extending down to 36,037 feet (10,984 m).
The Nile is the longest river in the world, winding for 4,132 miles (6,650 km) through northeastern Africa. Lake Baikal in Russia is the largest and deepest freshwater lake, containing 5,521 cubic miles of water (23,013 cubic km) — a volume approximately equivalent to that of all five North American Great Lakes combined.
What makes Earth special?
Earth is unique because it is the only place in the universe known to host life. Some of the oldest evidence of microbial life suggests that it was already widespread on our planet 3.95 billion years ago, Live Science previously reported. Exactly how these microscopic creatures arose remains a mystery, though experts have proposed many theories.
Scientists estimate that there are as many as 1 trillion species on our planet, occupying niches that extend from the upper atmosphere to deep below the rocky surface. Bizarre and complex biospheres exist around hydrothermal vents at the ocean's bottom and in just about every rock and crevice ever explored, Live Science previously reported. Whether this means organisms exist elsewhere in the solar system or beyond remains an open question, but the diversity of life on Earth has given scientists hope that life might exist in extreme environments throughout the universe.
Additional resources
- Learn how to measure Earth's shape and size in this blog post (opens in new tab) from physicist Matt Strassler.
- Explore NASA's latest information (opens in new tab) about Earth.
- Marvel at the beauty of our planet in this photo gallery (opens in new tab) from NASA.
Bibliography
Bishop, B. C. (2021, May 13). Mount Everest. Britannica. https://www.britannica.com/place/Mount-Everest (opens in new tab)
Caltech Infrared Processing and Analysis Center. (n.d.). What is Earth made of? Cool Cosmos. Retrieved March 25, 2022, from https://coolcosmos.ipac.caltech.edu/ask/58-What-is-Earth-made-of- (opens in new tab)
Geoscience Australia. (n.d.). Area of Australia - states and territories. Australian Government. Retrieved March 25, 2022, from https://www.ga.gov.au/scientific-topics/national-location-information/dimensions/area-of-australia-states-and-territories (opens in new tab)
McColl, R. W. (Ed.). (2005). Encyclopedia of world geography. Facts on File. https://books.google.com/books?id=DJgnebGbAB8C&pg=PA215&redir_esc=y#v=onepage&q&f=false (opens in new tab)
NASA. (1976). U.S. Standard Atmosphere, 1976. NASA Technical Reports Server. https://ntrs.nasa.gov/citations/19770009539 (opens in new tab)
NASA Goddard Space Flight Center. (2015, December). The Milky Way galaxy. https://imagine.gsfc.nasa.gov/science/objects/milkyway1.html
National Oceanic and Atmospheric Administration. (n.d.). Teacher background information: Earth's climate [PDF]. https://gml.noaa.gov/infodata/lesson_plans/Teacher%20Background%20Information-%20Earth's%20Climate.pdf (opens in new tab)
Nations Online. (n.d.). Countries of the Americas. Retrieved March 25, 2022, from https://www.nationsonline.org/oneworld/america.htm (opens in new tab)
Robertson, E. C. (2011, January 14). The interior of the Earth. U.S. Geological Survey. https://pubs.usgs.gov/gip/interior/ (opens in new tab)
Sharp, T. (2021, July 6). How big is Earth? Space.com. https://www.space.com/17638-how-big-is-earth.html (opens in new tab)
Sharp, T., & Urrutia, D. E. (2022, January 21). How far is Earth from the sun? Space.com. https://www.space.com/17081-how-far-is-earth-from-the-sun.html (opens in new tab)
Zell, H. (2017, August 7). Earth's atmospheric layers. NASA. https://www.nasa.gov/mission_pages/sunearth/science/atmosphere-layers2.html (opens in new tab)
