Explain what the word theory means.
How did the land-bridge form?
It was always there.
The water dried out because of hot weather.
The glaciers froze over during the Ice Age allowing them safe travel across.
Why did they migrate over the land-bridge?
They migrated because they wanted to look for new farm land.
They were following the herds of animals.
They were traveling to find shelter.
They were trying to find new land to live in.