First, use the globe on the left to take a look at the moon. As you can see, the moon is covered in craters. Because there is no air on the moon, and no tectonic plate movement, craters do not weather away, meaning that the moon's surface retains the scars of every object that has hit it in the past. Most of the moon's craters are thought to have been formed over 3.8 billion years ago. Our Solar System was formed around 4.6 billion years ago, and in the period directly after its formation, millions of small astronomical objects flew around colliding with each other repeatedly.
The Tycho Crater. One of the youngest craters on the moon's surface, thought to have been formed by a collision 100 million years ago. © NASA
Not only the moon, but in fact many of the bodies in our Solar System are covered in craters. One of the best known of these craters is that on Mimas, one of the moons of Saturn. It is known as the Herschel Crater, after the discoverer of Mimas, William Herschel. Measuring 130km across, the crater occupies a third of the moon's diameter. Its size suggests a major collision that Mimas may have barely survived, but exactly when the object hit is not known. It has left Mimas bearing a remarkable resemblance to the Death Star of Star Wars fame. 
Mimas, one of Saturn's moons, photographed from the planetary explorer Cassini © NASA
The surfaces of our moon and of Mimas are still pocked by thousands, if not tens of thousands of craters, so why are so few craters found on Earth? Obviously, like the moon and Mimas, our planet must have been hit by many celestial objects, leaving innumerable craters. However, for a number of reasons, such as the presence of air and sea, leading to erosion of craters by wind and rain, and the shifting of the continents, over the millennia almost all these craters have disappeared. At present there are around 180 known impact craters on Earth, ranging in age from two billion to just a few thousand years old. The globe on the left shows the distribution of these craters, indicating that most are found on the older land masses such as Australia and North America. These have only been identified as impact craters in the past 40 years or so, the result of a detailed global study of craters conducted as part of the Apollo Program in the 1970s.
Viewed like this, it is possible to see, albeit indistinctly, how our planet became the place it is today in the same way as the moon: by colliding with other bodies in space.
*Opinion is divided as to whether some craters have been formed by impact or volcanic activity. For Earthrium our source was the Earth Impact Database administered by the University of New Brunswick in Canada.