Rocks brought back from the moon by astronauts are about 4,500 million years old. Many meteors that fall to Earth are about 4,500 million years old also. Because the moon, the earth, and the meteors probably formed at the same time, when the entire solar system formed, we can logically conclude that the earth itself is about 4,500 million years old even though no earthly rock that old has yet been found. Minnesota is host to some of the oldest rocks on earth. Parts of the Morton Gneiss (pronounced "nice") in western Minnesota have been dated at 3,600 million years before present. Rocks as old or older than these are rare on earth because geologic processes on and within our active planet tend to recycle old rocks and produce younger ones. Only in Minnesota, northwestern Canada, Greenland, Siberia, South Africa, and Australia have remnants of very old rocks been preserved.