Every age on this page is answered by fossils alone: the rock database we use for the wider region does not reach Britain. 3,083 fossils have been recorded around this city, and at 66, 150 and 200 million years ago the ones whose age range reaches those moments are sea creatures. At 250 million years ago this page has to say something stranger: 120 fossils sit in that age's group and not one of them has an age range that reaches the age itself. At 66 million years ago it happens the other way round — the group is empty, and 16 fossils have ranges wide enough to cover it. One age also has a rock answer of a different kind: the geological map names the unit under this city, though it does not say what that rock formed in.
The answer, age by age
Five ages in the past of this place, each one a window rather than a day. Each says which witness spoke — and where our evidence cannot answer yet, it says that too.
“Ma” means millions of years ago. The dashed mark means our sources have nothing for that age — which is a finding, not a fault.
The same question, asked two ways
A fossil is not dated to a moment. It is dated to a stretch of time, and that stretch can be wider than the gaps between the ages on this page. So there are two fair ways to ask which fossils belong to an age, and this record answers both.
A full group that answers nothing — around 250 million years ago
120 fossils are grouped with this age, because this moment is the closest of the five to where their own age ranges sit. Not one of those ranges actually reaches 250 million years, so for this exact age the local witness has nothing to offer. The group is full and the answer is still empty.
An empty group that answers — around 66 million years ago
Here it happens the other way round. No fossil near this city is grouped with this age at all, and yet 16 of them have an age range wide enough to cover 66 million years. They are counted at a different age, and they still reach this one.
Where the two agree — around 200 million years ago
1,733 fossils are grouped with this age and 169 of them have a range reaching it. The closest was dug up about 3.2 km away — near the city, never under it.
Neither way of counting is a trick, and neither is the right one. They answer different questions: one asks which fossils are nearest to this moment in time, the other asks which fossils could have been alive at it. Every fossil in this record belongs to exactly one group, and a fossil’s own age range is wide enough to cover more than one moment.
It is worth knowing that a number in a science story is always the answer to a particular question, and that changing the question changes the number without anyone being wrong.
Travel back in time
The plate model places this ground at all five ages, each one further south than the last as the rows go back. The model returns a position, and a position is not a description of the place: it says where this piece of the Earth’s surface was, never what was on top of it.
250
million years agojump to the evidence250 million years ago, the plate model puts this ground about 12° north of the equator. This is one of the ages the models argue about most: published reconstructions put it as much as 6.4° of latitude apart, which is several hundred kilometres. Treat it as one model's answer, not a photograph.
200
million years agojump to the evidence200 million years ago, the plate model puts this ground about 18° north of the equator. Published models disagree by about 4.3° of latitude here — a few hundred kilometres — so it is one model's answer, not a photograph.
150
million years agojump to the evidence150 million years ago, the plate model puts this ground about 23° north of the equator. Published models disagree by about 4.4° of latitude here — a few hundred kilometres — so it is one model's answer, not a photograph.
100
million years agojump to the evidence100 million years ago, the plate model puts this ground about 33° north of the equator. This is one of the ages the models argue about most: published reconstructions put it as much as 5.4° of latitude apart, which is several hundred kilometres. Treat it as one model's answer, not a photograph.
66
million years agojump to the evidence66 million years ago, the plate model puts this ground about 44° north of the equator. Published models disagree by about 3.8° of latitude here — a few hundred kilometres — so it is one model's answer, not a photograph.
What was the water doing?
Five ages, oldest first. Each one has two kinds of witness — the rock of the wider region, and the fossils dug up near the city — and they are kept apart on purpose, because they are answers to different questions.
Each age here is a marker on the timeline, not a single day. The evidence that belongs to it comes with an age range of its own that overlaps the marker — so it can tell you what this stretch of time was like, and never what was happening on one exact date.
Our evidence has no witness here
Around 250 million years ago
250 million years ago, the plate model puts this ground about 12° north of the equator. This is one of the ages the models argue about most: published reconstructions put it as much as 6.4° of latitude apart, which is several hundred kilometres. Treat it as one model's answer, not a photograph.
An open question
Neither of the evidence sources we use can answer this one: the regional rock database does not cover this place at all, so it has nothing to say about 250 million years ago, and no fossil dug up nearby covers that age either. That is a real gap in the evidence, not a gap in the past — and saying so is more useful than guessing.
Only the fossils speak
Around 200 million years ago
200 million years ago, the plate model puts this ground about 18° north of the equator. Published models disagree by about 4.3° of latitude here — a few hundred kilometres — so it is one model's answer, not a photograph.
The rock of the region
The geological map does answer here: the rock mapped at this point is the Lias Group, dated 170.3 to 208.5 million years, a range that contains 200 million years ago. What the map does not record is what that rock formed in, so this source can name the rock and cannot answer the water question.
The fossils dug up nearby
169 fossils dug up near Bath have an age range covering 200 million years ago: 169 from the sea, 0 from land. The closest of them was found about 3.2 km away — near the city, never under it.
Only the fossils speak
Around 150 million years ago
150 million years ago, the plate model puts this ground about 23° north of the equator. Published models disagree by about 4.4° of latitude here — a few hundred kilometres — so it is one model's answer, not a photograph.
The rock of the region
The regional rock record does not cover this place at all, so there is no regional answer for 150 million years ago.
The fossils dug up nearby
125 fossils dug up near Bath have an age range covering 150 million years ago: 125 from the sea, 0 from land. The closest of them was found about 11 km away — near the city, never under it.
Only the fossils speak
Around 100 million years ago
100 million years ago, the plate model puts this ground about 33° north of the equator. This is one of the ages the models argue about most: published reconstructions put it as much as 5.4° of latitude apart, which is several hundred kilometres. Treat it as one model's answer, not a photograph.
The rock of the region
The regional rock record does not cover this place at all, so there is no regional answer for 100 million years ago.
The fossils dug up nearby
97 fossils dug up near Bath have an age range covering 100 million years ago: 96 from the sea, 1 from land. The closest of them was found about 23 km away — near the city, never under it.
Only the fossils speak
Around 66 million years ago
66 million years ago, the plate model puts this ground about 44° north of the equator. Published models disagree by about 3.8° of latitude here — a few hundred kilometres — so it is one model's answer, not a photograph.
The rock of the region
The regional rock record does not cover this place at all, so there is no regional answer for 66 million years ago.
The fossils dug up nearby
16 fossils dug up near Bath have an age range covering 66 million years ago: 16 from the sea, 0 from land. The closest of them was found about 23 km away — near the city, never under it.
What was dug up nearby?
Every fossil below was dug up somewhere around Bath, never underneath it, so each carries the distance to where it was actually found. The ages are ranges rather than dates, which is why the same fossil can be grouped with one age and still cover another.
Around 100 million years ago
A Gemmarcula from around this time (its own age range is 113.2–121.4 million years) was dug up about 19 km from here, in the Sandgate.
An Arenaciarcula fittoni from around this time (its own age range is 113.2–121.4 million years) was dug up about 19 km from here, in the Sandgate.
An Oblongarcula oblonga from around this time (its own age range is 113.2–121.4 million years) was dug up about 19 km from here, in the Sandgate.
Around 150 million years ago
A Megalosaurus from around this time (its own age range is 165.3–168.2 million years) was dug up about 0.6 km from here, in Somerset.
A Coenastraea from around this time (its own age range is 168.2–170.9 million years) was dug up about 0.6 km from here.
A Cyathophora pratti from around this time (its own age range is 165.3–168.2 million years) was dug up about 0.6 km from here.
Around 200 million years ago
A Plesiosaurus subtrigonus from 200 million years ago was dug up about 3.2 km from here, in Somerset.
A Binoculites terquemi from 200 million years ago was dug up about 7.0 km from here, in the Blue Lias.
A Binoculites jurassica from 200 million years ago was dug up about 7.0 km from here, in the Blue Lias.
Around 250 million years ago
A Clevosaurus sectumsemper from around this time (its own age range is 227.3–237 million years) was dug up about 26 km from here, in South Gloucestershire.
A Diphydontosaurus avonis from around this time (its own age range is 227.3–237 million years) was dug up about 26 km from here, in South Gloucestershire.
A Lepidosauria from around this time (its own age range is 227.3–237 million years) was dug up about 26 km from here, in South Gloucestershire.
We show these places to the nearest few kilometres rather than pinning them exactly. The scientists who recorded them know the spot far better than that — the full record is one click away in the Paleobiology Database, and it is free for anyone to read. We round them here because a map made for children is not a map for digging things up, not because anything is being hidden.
The rock the map shows here
Lias Group — described by the map as mudstone, siltstone, limestone and sandstone, and dated between 170.3 and 208.5 million years old. Of the five ages on this page, 200 million years ago falls inside that range.
The same spot, on three maps
Mesozoic sedimentary rocks — 66 to 100.5 million years · world map
Middle Jurassic limestone — 163.5 to 174.1 million years · continent map
Lias Group — 170.3 to 208.5 million years · country map
Those are three answers for one spot, and they do not match. A map of the whole world has to simplify; a map of one country has room for more detail. The more local the map, the more it can say — which is why the last line is the one this page quotes.
Our rock database has no column for this city, so the ages above rest on fossils. The geological map is a different source and it does answer here: it names the unit under this point and dates it, and one of the ages on this page falls inside that date range.
What the map does not record is what that rock formed in. It is a map of what is there, not a description of the world that made it, and we do not fill that part in.
This ground has moved a long way north. The plate model puts it in the tropics at the oldest age on this page, and at its present latitude today.
The rock at the surface today is younger than all of it. The geological map of this exact point returns Mesozoic sedimentary rocks (Late Cretaceous), Middle Jurassic limestone (Middle Jurassic), Lias Group (Mesozoic).
This page says nothing about the hills, the valley or the hot springs the city is known for. We have no source for how any of them formed, so we do not guess.
Try it yourself
The sea creatures in this record lived in water, and that water is still here, still going round. Some of it is in the glass beside you.
This is a good page for how a method decides what you can see. Ask which fossils are nearest an age and you get one number; ask which fossils could have been alive at it and you get another. On this page the two answers swap places between the oldest age and the youngest.
If a fossil could be anywhere between 200 and 250 million years old, which age should it be counted at — and what would you lose by choosing either one?
How sure are we?
Column facts describe an area of thousands to tens of thousands of km², centred tens of kilometres from the town coordinate. They are claims about a region, never about the rock beneath the town.
Fossil facts are a bounding-box sample around the town, each with its own distance from it; a fossil is never "here". The absence of fossils is not evidence of the absence of life — only of the absence of a recorded, published dig in this box.
Positions are model outputs, not observations. Independent plate models disagree by hundreds of kilometres at these ages, and that spread is the honest size of the uncertainty.
The land/sea question is answered only by the regional rock and the local fossils, separately, and never by the reconstruction — which says where this ground was and cannot say whether it was wet. There is deliberately no single field holding a one-word answer, because answering in one word would require merging a regional claim with a local one (CLAUDE.md rule 5). The nearby fossils are reported as a census of what has been found — which kinds are present, and how many of each — and never counted into a verdict: occurrence records are not statistically equivalent observations, so a plurality of them cannot establish an environment (science review, 2026-08-30).
Fossils are binned to their nearest slice age by age-range midpoint, with boundaries at the inter-slice midpoints 83, 125, 175 and 225 Ma. Those boundaries are an editorial choice, not a published stratigraphic scheme; a reviewer may prefer stage boundaries. Every occurrence keeps its own age range so the choice can be re-examined.
Sources
Macrostrat — the rock of the regionRead from version 2.3.9 of its data service on 30 August 2026.Peters, S.E. et al. Macrostrat: a platform for geological data integration and deep-time research. https://macrostrat.org, accessed on (date)Palaeogeography: Wright, N., Zahirovic, S., Müller, R. D., and Seton, M. Towards community-driven paleogeographic reconstructions: integrating open-access paleogeographic and paleobiology data with plate tectonics. Biogeosciences 10:1529-1541
The Paleobiology Database — the fossils dug up nearbyPBDB publishes no dataset version string; the data-service path (data1.2) and the datainfo access_time bound this claim.Fossil occurrence data from the Paleobiology Database (https://paleobiodb.org), released under CC0 1.0.Palaeo-coordinate cross-check (Paleobiology Database `pgm=gplates`): Wright et. al., 2013; Towards community-driven paleogeographic reconstructions.Palaeo-coordinate cross-check (Paleobiology Database `pgm=scotese`): Scotese, C.R., 2021. An Atlas of Paleogeographic Maps: The Seas Come In and the Seas Go Out, Annual Reviews of Earth and Planetary Sciences, v. 49, p. 669-718.Palaeo-coordinate cross-check (Paleobiology Database `pgm=seton`): Seton et. al., 2012; Global continental and ocean basin reconstructions since 200 Ma.
The EarthByte plate model — where this ground used to beMULLER2019 version 3.0, run with pyGPlates 1.0.0, licensed CC BY 4.0.GPlates: Müller, R. D., Cannon, J., Qin, X., Watson, R. J., Gurnis, M., Williams, S., Pfaffelmoser, T., Seton, M., Russell, S. H. J., Zahirovic S. (2018). GPlates: Building a virtual Earth through deep time. Geochemistry, Geophysics, Geosystems, 19, 2243-2261. https://doi.org/10.1029/2018GC007584Reconstructions computed with the GPlates Web Service (EarthByte Group, The University of Sydney).Plate model: Müller, R. D., Zahirovic, S., Williams, S. E., Cannon, J., Seton, M., Bower, D. J., Tetley, M. G., Heine, C., Le Breton, E., Liu, S., Russell, S. H. J., Yang, T., Leonard, J., and Gurnis, M. (2019), A global plate model including lithospheric deformation along major rifts and orogens since the Triassic. Tectonics, vol. 38, https://doi.org/10.1029/2018TC005462. Licensed CC BY 4.0.Plate model: Zahirovic, S., Eleish, A., Doss, S., Pall, J., Cannon, J., Pistone, M., Tetley, M. G., Young, A., & Fox, P. (2022). Subduction kinematics and carbonate platform interactions. Geoscience Data Journal, 9(2), p.371-383. Licensed CC BY 4.0.Coastline and static-polygon data by the EarthByte Group, licensed CC BY 3.0 Unported.
This record was assembled on from the datasets above. The ancient positions are reconstructions from a published plate model, not observations.