Why Earth has Fewer Craters than Moon

Plate Tectonics and Geological Activity Destroy Earth's Craters

Apr 20, 2009

The Moon's surface is littered with meteorite impact craters, but Earth has very few because geologic and plate tectonic activity destroyed ancient impact craters.

A view of the Moon through a small telescope shows that its surface is covered with a very large number of craters. Earth's surface contrasts with very few craters. Why?

Origin of Lunar Craters

Geologically, there are two common ways to form craters. One is by volcanic eruption and the other by meteorite impact. There are some volcanic craters on Earth, but meteorite impacts in the distant past formed the craters on the Moon. When a meteorite from space strikes a planet's or moon's surface, the impact has sufficient energy to explode and form a circular crater. Impact craters on the Moon and elsewhere in the solar system are nearly universally circular.

Meteoroids are debris left over from the formation of the solar system. As meteors strike moons or planets to form craters, they get used up. Hence, the major era of impact cratering in the solar system is over. Impact craters can still form but not as frequently as they formed 4 billion years ago, when the solar system was young.

One might think that Earth's atmosphere burns meteors to prevent meteorite strikes. This mechanism prevents very small craters from forming on Earth, but not large craters. Larger meteorites can penetrate the atmosphere to form a crater. If Earth's atmosphere does not prevent impact craters, why then does Earth have so few?

Craters Destroyed by Weathering and Erosion

It is well known that Earth's atmosphere causes weathering and erosion of geological features, including craters. Erosional processes can certainly wear away craters after they have formed on Earth, however erosion is not the primary reason that Earth has so few impact craters.

As evidence, consider Io and Europa, two of Jupiter's moons. Neither has a significant atmosphere to cause weathering and erosion. Yet neither has significant impact cratering. Other forces must be at work to destroy impact craters. Both Io and Europa have significant geological or tectonic activity. Jupiter's other two major moons, Ganymede and Callisto, have less geological activity and crater-covered surfaces.

Plate Tectonics and Geological Activity

The primary reason, therefore, that Earth has so few impact craters is that Earth has so much geologic and tectonic activity.

According to the theory of plate tectonics, Earth's crustal plates float on the mantle. Very slow convection currents in the mantle cause the tectonic plates to drift slowly. As the tectonic plates drift, they cause tectonic activity such as volcanoes and earthquakes. The drifting and tectonic activity obliterates craters and other existing geologic features. By reshaping Earth's surface geology, tectonic and geologic activity has destroyed impact craters on Earth.

There are a few craters from geologically recent impacts. Drifting tectonic plates have, however, completely swept away craters formed during the solar system's youth, the major era of cratering in the solar system.

The terms meteor, meteorite, and meteoroid seem to be used interchangeably in this article. They do however have distinct meanings. A chunk of debris drifting in space is a meteoroid. When it burns in Earth's atmosphere, it becomes a meteor. After striking the surface, it is a meteorite.