Why doesn’t the Earth have more craters? 8 – Science Mysteries Explained

Q:
A:
earth science
IDIOT’S GUIDES: SCIENCE MYSTERIES EXPLAINED
8
Why doesn’t the Earth have more craters?
When we look through a telescope at other rocky planets and moons in the Solar System,
we see they have one surface feature in common: craters. Lots and lots of craters, from
meteorite impacts. But from space, Earth appears to have no craters at all. Where are our
craters?
There are lots of craters, but they’re blurred and hidden because the Earth is unique in the Solar System.
We have two things no other planet has: oceans on the surface and lots of life. And continental drift plays a
role, too.
Though we don’t yet have a complete answer
for how the Solar System was formed, scientists
mostly agree that a large disc of matter orbiting the
Sun slowly clumped into the eight major planets.
But about 1 percent of the material instead formed
into trillions—yes, trillions—of rocks, comets, and
asteroids.
These objects move throughout the Solar
System in all sorts of crazy orbits, and over a long
enough period, thousands of them will eventually
hit a planet or a moon.
There was even a period in the Earth’s early
history where the number of “impacts” (rocks
hitting something) increased—it’s called the
Late Heavy Bombardment, and it’s why the
Moon has so many craters.
So did the Earth just escape getting hit?
Not at all—we’ve been smashed by our share
of space rocks. There is strong evidence that a
large object, probably a comet, hit what is now
Central America and killed o the dinosaurs.
If the Chixulub Impact, as it’s known, had hit
the Moon, there would be a huge round crater
for us to admire. So where’s the Chixulub crater
on Earth? Why can’t we see it?
EARTH SCIENCE
9
The crater is there all right, but it’s mostly under the
ocean. What parts remain on land have been eroded by
wind and rain, and the jungle has grown over the top. If
you use a satellite and specialized instruments, it’s quite
easy to see a distinct round geological shape hidden under
the familiar coastline of Central America.
Geologists have identified thousands of craters all over
Earth. Some of them have lakes in the middle, others are
buried under sand dunes, still others can only be detected
by the damage they did to the crust deep underground—all
surface features have eroded away.
Earth is unique in the Solar System because of our
water cycle (liquid oceans that evaporate to create rain on
land) and our abundance of life.
Rain and wind erode the distinctive crater walls,
smoothing out the jagged peaks you can still see on the
Moon. And plants grow too, making it hard for us to spot
craters under jungles or grasslands.
Over longer periods of time, the processes of plate tec-
tonics (the way sections of the surface of the Earth move
around on top of a liquid interior) jumble and change
many surface features. Valleys open up, mountains are
pushed into the sky, coastlines sink or rise. All of these
things destroy the delicate structure of an impact crater.
But there are still places on Earth where you can visit a
well-preserved crater. For instance, the central Australian
desert has several craters, such as at Wolf Creek. Because
these areas receive very little rainfall, have sparse plant
life, and are located far away from tectonic fault lines, the
land is rarely disrupted—and so the craters are preserved.
But compared to the craters on the Moon, some of
which are millions of years old, even craters like Wolf
Creek won’t last long. Within a few hundred thousand
years, they will literally blow away in the wind and fade
away as the surface of the Earth continues to change.