A land bridge is a strip of dry land that joins two landmasses normally separated by water. Most famous ones, such as Beringia and Doggerland, were shallow seabed that lay above the sea during the Ice Age, when sea level was far lower than it is now.
Key takeaways
- Land bridges appear where the sea between two landmasses is shallow enough to dry out when sea level falls.
- We checked 10 likely bridges against the grid, and all 10 are dry when the sea is 120 m lower.
- The Bering Strait floor is 55 m down today, so it dries at 80 m lower.
- A bridge on our map is a bathtub-model result, not proof of a walkable route.
How a land bridge forms
A land bridge needs two things: two landmasses close together, and a shallow seabed between them. Most of the world's coasts are fringed by a continental shelf, a gently sloping platform of seabed [2]. Where the shelves of two landmasses meet or overlap, the water over them can be shallow for hundreds of kilometres.
When sea level falls, that shallow water goes first. During the Last Glacial Maximum, ice sheets held so much water that the sea stood roughly 120 m lower than it does today [1]. A seabed less deep than that became dry land, and the landmasses on either side were joined.
Land bridges are temporary. When the ice melted, the sea rose and flooded them again. The speed and timing varied from place to place, so a bridge may have been open to animals and people for thousands of years and then closed quickly or slowly.
A land bridge is not always a narrow isthmus. Some, such as Beringia, were broad plains hundreds of kilometres wide. That is why researchers talk about the land, not only the route across it.
The map reads the depth of each site directly from the grid, then tells you the lowest sea level at which it would be dry. The Ice Age section of the homepage shows the biggest ones at once.
An example from our data
We checked 10 sites and found 10 dry at 120 m lower: Doggerland (North Sea), English Channel floor, Irish Sea floor, Beringia (Bering Strait), Beringia (Chukchi shelf), Sundaland (Java Sea), Sundaland (Gulf of Thailand), Sahul (Arafura Sea), Sahul (Gulf of Carpentaria) and Bass Strait (Tasmania).
They dry at different steps of the slider. The North Sea site of Doggerland is 43 m deep today, so it is dry at 50 m. The Bering Strait is 55 m deep and dries at 80 m. The Arafura Sea between Australia and New Guinea is 111 m deep, and needs the full 120 m.
That difference is the point: a bridge's depth tells you how far the sea had to fall before people and animals could cross.
The thing people get wrong
A dry patch on our map does not mean a bridge was open. The slider is a bathtub model that lowers the sea evenly on today's seabed. It ignores ice sheets, which blocked some routes, and ignores crust movement and seabed change since. A real bridge also needed a climate and a landscape that could be crossed, which the map does not show.
The map tells you where the seabed was shallow enough to be exposed, and no more.
Frequently asked questions
Why did land bridges appear in the Ice Age?
Because water was locked up in ice sheets, sea level fell and the shallow seabed between some landmasses became dry land.
Which land bridges does the map show?
It checks 10 well-known sites, including Doggerland, Beringia, Sundaland and Sahul, by reading their depth from the grid.
Sources
- Last Glacial Maximum, Wikipedia.
- Continental shelf, Wikipedia.
- Every figure from our own map is worked out from the datasets on the data sources page (checked against GEBCO_2026 grid).