Whichever theory is right, astronomers have figured out that it all probably happened about 5,500,000,000 years old! But other scientists besides astronomer have tackled this question. They tried to find the answer by studying how long it took for the earth to become the way we know it. They studied the length of time it takes to wear down to the oldest mountains, or the time needed for the oceans to collect the salt they now contain. After all their studies, these scientists agree with the astronomer: the earth is about 5,500,000,000 years old.
