Vickie Tolbert, age 10, of Tulsa, Okla., for her question:

Were Alaska and Asia ever joined?

The old earth is very, very old. The latest estimates say that she may have had three billion birthdays. In all that time there have been a great many changes. Time after time the seas have run over the land. At one time the California region was an island. At another time a wide sea stretched down the center of North America from the Arctic Ocean to the Gulf of Mexico. The region where the Rockies now stand was once a deep valley.

There were also times when new land areas arose from the sea. England was once joined to the mainland of Europe. At one time North America joined hands with Europe on one side and Asia on the other. There were land bridges over the northern oceans. One of these long arms reached from Alaska to Asia. In the long history of the earth this land bridge may have risen and fallen several times.

Most likely the Alaskan land bridge existed during the Ice Ages. At this time a great deal of the world's water was frozen in massive glaciers. That much water was stolen from the sea. The level of the oceans dropped all over the world.