Encyclopedic Entry

Deserts, such as Saudi Arabia (above) and Antarctica, are excellent places to search for meteorites.

Photograph by Thomas J. Abercrombie

Rocky Cookie
The best place to hunt for meteorites is in Antarctica. Because most of Antarctica is covered in ice and snow, rocky meteorites stand out like chocolate chips in a cookie.

Meteorite or Meteorwrong?
How can you tell if that rock you found fell from the sky? First of all, meteorites get burned when they enter Earths atmosphere, so they are usually black and crusty on the outside. Also, meteoriteseven stony meteoritescontain iron, so a magnet will stick to them.

Meteorites are meteors that fall to Earth’s surface. A meteor may also be called a shooting star or falling star.

Meteors were once meteoroids. Meteoroids are lumps of rock or iron that orbit the sun. Many were once part of larger bodies called asteroids, which orbit the sun between the paths of Mars and Jupiter in a region called the asteroid belt. Others come from the moon, Mars, and the tails of comets.

Dust-sized particles called micrometeorites make up 99 percent of the approximately 50 tons of space debris that fall through Earth’s atmosphere each day.

As meteors fall into Earth’s atmosphere, the gases surrounding them briefly light up. At this point, meteoroids become meteors, or shooting stars. Most meteors are too small to reach the surface of the Earth. They burn up and disintegrate in Earth’s atmosphere.

Very large meteors might explode before reaching the Earth’s surface. This is rare. In 1908, a meteor exploded about 10 kilometers (6 miles) over the Tunguska River in Siberia, Russia. The so-called Tunguska Event is considered an impact, even though the meteor did not actually hit the Earth and become a meteorite. The Tunguska Event instantly knocked down about 80 million trees in the Siberian forest. Many scientists say the explosion was larger than the most devastating nuclear weapon ever detonated.

Types of Meteorites

Scientists have collected hundreds of meteorites. They have divided the meteorites into three main types: stony, iron, and stony-iron.

Stony meteorites are made up of minerals that contain mostly silicon and oxygen. They also contain some metalnickel and iron. There are two types of stony meteorites. Chondrites are the most common type of meteorite, accounting for 86 percent of all meteorites that have fallen to Earth. They are named for the hardened droplets—or chondrules—of lava embedded in them. Achondrites do not contain these droplets. They are very rare, constituting about 3 percent of all known meteorites. They form in the outer layer of asteroids, which is similar to Earth’s crust.

Iron meteorites are mostly made of iron and nickel. They come from the cores of asteroids and account for about 5 percent of meteorites on Earth.

Stony-iron meteorites have nearly equal amounts of silicate minerals and metal in them. One group of stony-iron meteorites, the pallasites, contains yellow-green olivine crystals encased in shiny metal.

The largest meteorites leave enormous holes in the ground called impact craters. The best example of an impact crater in the United States is Meteor Crater, near Winslow, Arizona. There, more than 20,000 years ago, a meteorite weighing about 270,000 tons slammed into the Earth, making a hole 1.3 kilometers (.8 miles) wide and 175 meters (575 feet) deep.

Many scientists believe a large meteorite triggered the extinction of the dinosaurs 65 million years ago. They believe the Chicxulub Crater in the Yucatán Peninsula in Mexico is the site of that meteorite’s impact.

Vocabulary

Term Part of Speech Definition Encyclopedic Entry

achondrite

Noun

type of stony meteorite containing no hardened droplets (chondrules).

asteroid

Noun

irregularly shaped planetary body, ranging from 6 meters (20 feet) to 933 kilometers (580 miles) in diameter, orbiting the sun between Mars and Jupiter.

asteroid belt

Noun

area of the solar system between the orbits of Mars and Jupiter filled with asteroids.

atmosphere

Noun

layers of gases surrounding a planet or other celestial body.

Encyclopedic Entry: atmosphere

chondrite

Noun

type of stony meteorite containing hardened droplets, called chondrules, of silicate minerals.

chondrule

Noun

small droplet of silicate mineral found in stony meteorites.

core

Noun

the extremely hot center of Earth, another planet, or a star.

Encyclopedic Entry: core

detonate

Verb

to cause something to explode.

devastate

Verb

to destroy.

disintegrate

Verb

to fall apart and disappear.

dust

Noun

microscopic particles of rocks or minerals drifting in space. Also called cosmic dust or space dust.

forest

Noun

ecosystem filled with trees and underbrush.

gas

Noun

state of matter with no fixed shape that will fill any container uniformly. Gas molecules are in constant, random motion.

impact

Noun

collision or crash.

impact crater

Noun

circular surface depression made by the impact of a meteorite.

iron meteorite

Noun

rock, made of iron and nickel, that has crashed to Earth from outside the atmosphere.

Jupiter

Noun

largest planet in the solar system, the fifth planet from the Sun.

lava

Noun

molten rock, or magma, that erupts from volcanoes or fissures in the Earth's surface.

magnet

Noun

material that has the ability to physically attract other substances.

Mars

Noun

fourth planet from the sun, between Earth and Jupiter.

metal

Noun

category of elements that are usually solid and shiny at room temperature.

meteor

Noun

rocky debris from space that enters Earth's atmosphere. Also called a shooting star or falling star.

Encyclopedic Entry: meteor

meteorite

Noun

type of rock that has crashed into Earth from outside the atmosphere.

Encyclopedic Entry: meteorite

meteoroid

Noun

small, rocky body traveling around the sun.

Encyclopedic Entry: meteoroid

micrometeorite

Noun

dust-size particle of space debris that burns up as it enters Earth's atmosphere.

mineral

Noun

inorganic material that has a characteristic chemical composition and specific crystal structure.

nickel

Noun

chemical element with the symbol Ni.

nuclear weapon

Noun

explosive device that draws power from the splitting and combining of atomic nuclei.

olivine

Noun

type of silicate mineral.

orbit

Verb

to move in a circular pattern around a more massive object.

Encyclopedic Entry: orbit

stony-iron meteorite

Noun

rock, made of nearly equal parts metal and silicate minerals, that has crashed to Earth from outside the atmosphere.

stony meteorite

Noun

rock, made of silicate minerals, that has crashed to Earth from outside the atmosphere.

Credits

Media Credits

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Writer

Kim Rutledge
Melissa McDaniel
Diane Boudreau
Tara Ramroop
Santani Teng
Erin Sprout
Hilary Costa
Hilary Hall
Jeff Hunt

Illustrator

Tim Gunther
Mary Crooks, National Geographic Society

Editor

Kara West
Jeannie Evers

Educator Reviewer

Nancy Wynne

Producer

Caryl-Sue, National Geographic Society

Sources

Dunn, Margery G. (Editor). (1989, 1993). "Exploring Your World: The Adventure of Geography." Washington, D.C.: National Geographic Society.

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