The Last Glacial Maximum was the time, roughly 26,000 to 20,000 years ago, when ice sheets were at their largest. So much water was locked up in ice that sea level stood well over 100 metres below today's, exposing wide stretches of shallow seabed as dry land.
Key takeaways
- The Last Glacial Maximum was the most recent time the ice sheets reached their greatest extent, and sea level was roughly 120 m lower than today.
- Falling seas turned shallow shelf into land: at 120 m down, the bathtub model on our map exposes 21.7 million km² of seabed.
- All 10 land bridges we checked are dry at 120 m lower, including Doggerland and Beringia.
- The Ice Age map is a simple bathtub model, not a reconstruction of the real coastline.
How the Last Glacial Maximum changed the sea
The Last Glacial Maximum, or LGM, is the part of the last ice age when ice sheets were at their biggest. It is usually placed between about 26,000 and 20,000 years ago [1]. Vast ice sheets covered most of Canada and much of northern Europe [1]. That ice was made of water that had once been in the sea, so the ocean got smaller.
The result was a sea level roughly 120 m lower than today. One source gives about 125 m around 21,000 years ago, and other estimates differ [1]. Because the world's shelves are shallow and gently sloping, a fall of that size did not just pull the coast back a little. It exposed large areas of seabed.
Land that is now sea became dry ground that animals, plants and people could cross. Britain was joined to Europe, Asia to North America, and the islands of South East Asia to the mainland. When the ice melted, the sea rose again and these links drowned.
The Ice Age section of the homepage shows this on the map. This page goes a little further into what the figure means and where it stops being reliable.
An example from our data
Set the slider to 120 m down and the map exposes 21.7 million km² of seabed, equal to 14.8% of today's land area. The sea that remains is 94% of its present extent. The full step is on the 120 m page.
The change happens in stages as the slider goes down. At 50 m the Doggerland site in the North Sea is already dry, since the point we sampled there is 43 m down today. At 80 m the Bering Strait floor, 55 m down today, has joined Asia and North America. The Arafura Sea, between Australia and New Guinea, is deeper at 111 m and only dries at 120 m.
Across all 10 land bridges we checked, 10 are dry at 120 m lower. The list is 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).
The North Sea shows how much shallow shelf there is: 84.5% of it is dry at 120 m lower, and 93.6% of it is shallower than 200 m today. See the North Sea page.
The thing people get wrong
People often read the Ice Age map as a picture of the real coastline 20,000 years ago. It is not. Our slider is a bathtub model: it lowers the sea by the same amount everywhere, on today's seabed.
Three things are missing. Ice sheets covered some of the land the map shows as free of ice. The crust under and around the ice was pressed down and has since moved, a process called isostasy [2]. And rivers, sediment and sea level rise itself have reshaped the seabed since. The real coast was in different places, and the real sea level also varied from region to region.
So treat the map as a good guide to how much shelf is shallow enough to have been dry, not as a surveyed ancient map.
Frequently asked questions
When was the Last Glacial Maximum?
It is usually dated to between about 26,000 and 20,000 years ago, although researchers choose slightly different dates for the start and end.
How much lower was sea level?
Roughly 120 m lower than today is the figure our map uses. Published estimates vary, and one source puts it at about 125 m around 21,000 years ago.
Is the 120 m step on the map an exact reconstruction?
No. It lowers today's sea by 120 m everywhere on today's seabed, so it ignores ice sheets, crust movement and seabed change since.
Sources
- Last Glacial Maximum, Wikipedia.
- Isostasy, Wikipedia.
- Every figure from our own map is worked out from the datasets on the data sources page (checked against GEBCO_2026 grid).