Some interesting questions about craters...

How are terrestrial impact craters recognized by scientists?

There are many kind of craters on Earth, and not all of them are generated by impacts (for example, many craters have been generated by volcanos). So, how can scientists distinguish impact craters from other kinds of structures?
First of all, a crater has to be identified, and this is not always easy on Earth. In fact, if on the Moon, craters are very visible (click here to see some beautiful craters on the Moon), on Earth there are many mechanisms that wipe them away. Furthermore, many craters happen to be in the water, and in this case, recognizing them is even harder. Luckily, today scientists are helped in this task by satellitary photography and spacecraft orbital imagery.

On the left, crater Bessel on the Moon
( photo NASA, Apollo)
On the right, a Shuttle image of
Manicougan craters. ( NASA/LPI)

After the crater has been identified, how can scientists prove its meteoric origin? Apart from the morphology and the characteristic shape of the impact crater, there are several markers that have been used in the past and that are still used today :


What happens after a crater is formed on Earth?

A last question that needs to be answered about impact craters is: if all the bodies of the solar system have gone through similar periods of bombardment, why do craters around the planets of solar system (for example craters on Earth, on the Moon or on other planets) appear so different ? In other word which geological mechanisms take place on the Earth's crust to change the crater's aspect ?
A first explanation is based on the fact that the surface of the Earth is still very active, while on some other planets and moons (such as the Moon, Mars and Mercury) the geological processes stopped millions of years ago. For this reason, craters due to bombardment have been clearly recorded on the surface of the Moon and impact craters are still visible. On Earth, however, craters are continually erased by erosion and redeposition as well as by volcanic resurfacing and tectonic activity.