What did Earth look like 100 million years ago?
Warmer, wetter, and with far more shallow sea than today. On this reconstruction 66.2% of the world's surface was below sea level — and much of what was under water was shallow, flooding the middle of continents rather than sitting out in the deep ocean.
AI reconstruction — not a photograph · Shutterstock AI/Shutterstock.com · Shutterstock Standard License
The world about 100 million years ago. The source calls this map the Early Cretaceous.
- Land
- Shallow sea
- Deep ocean
Yellow is land, mid-blue is shallow sea, dark blue is deep ocean. The map is drawn flat, so places near the poles look wider than they really are.
This is one model’s answer, not a photograph. It shows the world about 100 million years ago — the age of the map itself, which is the closest the source gets to the ages on this site.
Map data: Scotese, C. R., & Wright, N. M. (2018). PALEOMAP Paleodigital Elevation Models (PaleoDEMS) for the Phanerozoic (Version 2) [Data set]. Zenodo. https://doi.org/10.5281/zenodo.5460860 Licensed CC BY 4.0. Grid 361×181 at 1° — about 111 km per cell at the equator, so nothing the size of a town can be read from it.
Look at how much of it is pale blue
The mid-blue on that map is shallow sea, and there is a striking amount of it lying across the middle of continents rather than around their edges. North America has a seaway running up through it. Europe is a scatter of islands. That is what the phrase “this was underwater” usually means on this site: not deep ocean, but a warm shelf sea a few tens of metres deep, sitting on top of a continent.
Across this whole map 66.2% of cells are below sea level. Today the figure is about 71%, so this world was not wetter overall — the water was in different places, and a lot of it was on top of land that is dry now.
There is a proper name for a sea that sits on top of a continent rather than between them: an epeiric sea. The people who made this map use it too — they describe the pale blue as “the shallow shelves and the flooded portions of the continents (epeiric seas)”. Worth knowing, because almost every time this site says a British town was under the sea, this is the kind of sea it means: shallow, warm, and sitting on land rather than off the edge of it.
Real photograph · Sven Hansche/Shutterstock.com · Shutterstock Standard License
This map cannot tell you about your town
Each square on it is one degree across — about 111 km at the equator. A town is a dot inside one square, and the answer for a dot is not the answer for the square.
There is a harder reason too, and it is worth knowing. This map comes from one reconstruction of the ancient world. The place-by-place pages on this site use a different one, plus the rocks and fossils people have actually dug up. We compared them: at the seven towns on this site they give the same land-or-sea answer nine times out of seventeen, and a different one the other eight. Neither is lying. They are two estimates, and estimates differ.
So for a real place, go and read what was dug up there: Brighton, Hull and London all have chalk and sea fossils from around this age, and those pages say what the rock says.
Map built from data
The same world about 100 million years ago, as a picture you can save and use in class, with its credit underneath.
- Land
- Shallow sea
- Deep ocean
Yellow is land, mid-blue is shallow sea, dark blue is deep ocean. The map is drawn flat, so places near the poles look wider than they really are.
This is one model’s answer, not a photograph. It shows the world about 100 million years ago — the age of the map itself, which is the closest the source gets to the ages on this site.
Map data: Scotese & Wright (2018), PALEOMAP PaleoDEMs — rendered by triassicwater.com · CC BY 4.0
Map data: Scotese, C. R., & Wright, N. M. (2018). PALEOMAP Paleodigital Elevation Models (PaleoDEMS) for the Phanerozoic (Version 2) [Data set]. Zenodo. https://doi.org/10.5281/zenodo.5460860 Licensed CC BY 4.0. Grid 361×181 at 1° — about 111 km per cell at the equator, so nothing the size of a town can be read from it.
For teachers
For school
- North America has a seaway running up through it. Europe is a scatter of islands.
- Across this whole map 66.2% of cells are below sea level.
- Each square on it is one degree across — about 111 km at the equator.
Classroom prompt
Find the mid-blue on the map. If so much of this world’s land lay under a warm shelf sea, why does the page say it was not wetter overall than today?
Extension: two reconstructions gave different land-or-sea answers at eight of the seventeen checks made at this site’s towns. Which evidence would you ask for before choosing between them for one town?
Ages: spotting the shallow sea on the map works from about seven; the idea of an epeiric sea and the two disagreeing reconstructions suit pupils of about eleven upwards. That range is our teaching choice for this page, not a curriculum claim.
Where this comes from
- The maps
- PALEOMAP Paleodigital Elevation Models (PaleoDEMS) for the Phanerozoic, version 2. Scotese, C. R., & Wright, N. M. (2018). PALEOMAP Paleodigital Elevation Models (PaleoDEMS) for the Phanerozoic (Version 2) [Data set]. Zenodo. https://doi.org/10.5281/zenodo.5460860 Licensed CC BY 4.0. Read from a copy whose checksum is recorded in this repository, so the numbers on this page can be checked against the exact file they came from.
- How sure is this?
- Every map here is a reconstruction — an estimate built from evidence, not a photograph. Its authors call each one the “best guess” or average geography for the time it represents, which is a fair description and worth repeating. 1° cells — roughly 111 km at the equator. Nothing at the scale of a town can be read from this grid. The source grid is 5 million years. An age between two maps is NOT interpolated: the nearest map is used and its own age is what gets published.
One reconstruction among several. PALEOMAP draws the world here; MULLER2019 places individual points elsewhere on this site. They are different models and are never composited or averaged.
Read from the source archive on .
Where next
The seaway running up through North America on this map has its own page, the Western Interior Seaway, read from the rock under one city rather than from the map. For a world with the least water of all, go back another hundred million years to 200 million years ago, and the Ancient Earth pages gather the other ages.