Geode

Snowflake Obsidian

Depending on what type of rock it is,

a rock melts at temperatures between

1,300 and 2,400 degrees Fahrenheit

(700 and 1,300 degrees Celsius).

COMETS are balls of rock and ice—

sometimes called “dirty snowballs”—that are

heated by the sun and soar through space,

leaving glowing ribbons of dust behind them.

Asteroid

Meteoroid

Comet

METEOROIDS are rocks that range in size

from a grain of sand to a basketball. These

“shooting stars” streak through space and some-

times slam into the moon, Earth, and other planets,

breaking into fragments known as meteorites.

ASTEROIDS are gigantic chunks of

rocks and metal. They can weigh millions

of tons. The largest known asteroid is

650 miles (1,050 kilometers) in diameter.

It would take a person 352 hours,

or nearly 14 days, to walk around it.

The oldest known rocks on Earth were

formed billions of years before the sky

turned from green to blue, before dinosaurs

thundered across the earth, before humans

learned how to make fire. The oldest rocks

ever found are nearly 4.5 billion years old.

METEORITE FRAGMENTAlgeria,

4.4 billion years old

GREENSTONECanada,

4.28 billion years old

ZIRCON CRYSTALAustralia,

4.1 billion years old

LEWISIAN GNEISSScotland,

3 billion years old

GRANITEUnited States,

2.5 billion years old

The carpets of sand on the floors and shores of

oceans, lakes, and rivers come from larger rocks that

have been ground, through weathering, into tiny grains.

Considered by many to be the world’s largest rock, Australia’s

Mount Augustus is a sandstone rock with an elevation, or height,

of 3,628 feet (1,106 meters) above sea level—about 1,000 feet (305 meters)

higher than the world’s tallest skyscraper.