Early humans in North America

Available evidence indicates that modern humans crossed from Siberia to Alaska as glaciers began to retreat at the end of the last ice age - less than 20,000 years ago

1 15,000 years ago

Coast becomes ice-free allowing humans to travel overland

2 13,000 years ago

Retreat of glaciers opens up migration routes between the continents

Alaska

Bering Sea

Land bridge

at a time of lower sea levels

California

3 130,000 years ago

Mastodon bones 'processed' using hammerstones and stone anvils

Mexico

1 15,000 years ago

Coast becomes ice-free allowing humans to travel overland

2 13,000 years ago

Retreat of glaciers opens up migration routes between the continents

Alaska

Siberia

Bering Sea

Land bridge

at a time of lower sea levels

California

Pacific Ocean

3 130,000 years ago

Mastodon bones 'processed' using hammerstones and stone anvils

Mexico

Guardian graphic | Source: Nature, various sources