Geologists believe that between 280 million and 225 million years ago, the earth's previously separate land areas became welded into a landmass called Pangaea. About 120 million years ago, they believe, this landmass began to separate. As this happened, the Atlantic Ocean formed, dividing the Americas from Africa and Eurasia.
Hi Elizabeth--Try to avoid using About.com as a source. Instead, look for educational websites related to schools, museums, libraries, and research organizations. If you must, look at Wikipedia to see what sources are cited at the bottom of the page. That's a good place to start.