Researchers have modeled sea level changes on thousand-year timescales for the past 540 million years. These insights offer better tools for mapping subsurface layers used in energy and waste storage.
Earth’s sea levels have fluctuated ever since the planet first had oceans. Until recently, scientists could only estimate these changes over broad time intervals, typically spanning millions of years, by analyzing sediment layers and fossil evidence. Now, for the first time, researchers from Utrecht University, the United Kingdom, and the United States have managed to chart sea level changes on the scale of thousands of years across the past 540 million years.
Their findings, published on 3 July in Earth and Planetary Science Letters, offer new insights into the planet’s geological history. “Taking these rapid sea level variations into account is important for understanding the structure of the subsurface, and the applications to green energy resources,” the researchers explain.
Two main factors drive sea level: plate tectonics, which shape the depth of ocean basins, and the volume of land ice, which determines how much water fills them. “If you look at time intervals of roughly a million years, you can estimate an average sea level going back to the earliest fossil records, about 540 million years,” says Dr. Douwe van der Meer, a guest researcher at Utrecht University and the study’s lead author. “That level has shifted by as much as 200 metres. We suspected there were also large changes over much shorter timeframes, but the available data was too limited to resolve them.”
Geological tree rings
To assess sea level changes over shorter time periods, scientists turn to rock layers formed in the last few million years. Much like tree rings, sedimentary layers such as sandstone and claystone provide a record of environmental conditions. Claystone typically forms in deeper marine settings, while sandstone is deposited closer to shorelines. “We observe these layers alternating most clearly during cold climatic periods when ice covers the poles,” the researchers explain. During such times, the Earth’s axial wobble creates ice ages lasting tens of thousands of years, driving sea level fluctuations of up to 100 meters.
Until recently, scientists could not identify these rapid changes in sea level in the distant past. Van der Meer and his team addressed this by establishing a relationship between global climate and ice sheet volume using high-quality data from the last several tens of millions of years. “This gave us the most accurate information, where we have warm periods without ice, and cold periods with ice – as well as ice ages. We used that relationship to determine short-term variability further back in time, to 540 million years ago,” Van der Meer explains.
Their reconstruction of these short-term sea level changes showed strong alignment with fossil-based estimates. “This is the first time we have been able to quantify sea level in a consistent way for such short timescales,” says Van der Meer. In recent millions of years, recurring ice ages have caused sea levels to rise and fall by as much as 100 meters. In contrast, during the Jurassic and Cretaceous periods, when dinosaurs roamed the Earth, sea level variation was less extreme due to the absence of significant land ice. However, in the late Carboniferous, when giant dragonflies hovered over vast swamps in what is now the Netherlands, sea level shifts were much larger because of a massive southern hemisphere ice cap.
Applications for underground storage
Because we now know much more precisely what happened to sea levels in the past, researchers are able to make better maps of the Earth for all time periods. They can use these for climate and evolution models, and their response to sea level change. “High or low sea levels, it’s all happened before in the geological past,” Van der Meer says.
Knowledge of sea levels in the geological past has many different applications. Today, we seek methods for underground CO2 and hydrogen storage, or geothermal energy. Sandstone, deposited at low sea level, is important here because it can be used as a reservoir. Claystone, deposited at high sea level, acts as a seal through which water or CO2 cannot easily pass. Currently, suitable sites for storing radioactive waste are also being sought in these kinds of strata. “If we know that at a certain time global sea level was high, we also know that a relatively continuous layer of claystone would have been deposited. We can use that information to create a global layer map of sand and claystone, which helps us in the safe use of the subsurface.”
Reference: “Phanerozoic orbital-scale glacio-eustatic variability” by Douwe G. van der Meer, Lennert B. Stap, Christopher R. Scotese, Benjamin J.W. Mills, Appy Sluijs and Douwe J.J. van Hinsbergen, 1 October 2025, Earth and Planetary Science Letters.
DOI: 10.1016/j.epsl.2025.119526
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4 Comments
“Two main factors drive sea level: plate tectonics, which shape the depth of ocean basins, and the volume of land ice, which determines how much water fills them.”
Fundamentally, what is more important is the volume of ocean basins, and the volume of terrestrial land (and its density). If the land is worn down to a peneplane, then the volume of high-standing mountains is absent, and former mountains have been turned into sandstones and shales, which end up in the oceans. Shortly after orogenies, the volume of mountains is large; similarly, after extended eruptions of Large Igneous Provinces, the volume of basaltic terrestrial rocks will be much larger than several ten’s of millions of years later. It is all in flux, and we lack detail on the location, altitude, shape, and even area of all the terrestrial rocks because they are continuously eroded, worn away, and recycled as igneous intrusions and metamorphosed roof pendants. The eroded sediments largely end up in the oceans, displacing water, and reducing the effective volume of the ocean basins. It is just shear luck that some areas preserve fossils and escape erosion, allowing us to know that certain terrestrial organisms existed and tells us something about the environmental conditions, but giving us scant insight on how widespread they were, and how they varied with elevation. We have a better idea about the nature of marine organisms.
Also, what is an unstated assumption is that the volume of sea water, including liquid and frozen phases, has been essentially constant for the last 540 million years, and hasn’t been bound up chemically, isolated in lakes, retained in aquifers, diverted to the atmosphere, or temporarily removed from the oceans by subduction of plates. What do the phenomenally thick salt beds throughout the world tell us about evaporation of water and its temporary residency as the salt piles get thicker and thicker? The Clausius-Clapeyron relationship tells us that we can expect that during the Hothouse climates, much more of the water was to be found as vapor in the atmosphere and as droplets in clouds, and therefore, not residing in the oceans.
What this study is lacking is a concise definition of just what is being measured, and how they determined the volume of the land in the past without detailed topographic maps; similarly, there are no detailed bathymetric maps for the past. We can estimate the volume of existing marine sediments, but it is more difficult to be certain about the fraction that have been metamorphosed.
What this press release doesn’t make clear is that this research is supposedly about the role of glaciation in affecting the amount of water removed from the oceans, and the depression of the mantle under the glacial ice, while ignoring the other things I mention above. I don’t put a lot of faith in their claims, particularly their paleo-climate models.
So, right now the ocean levels are at their lowest point in all of the last 540 million years. Hmmmm….. So, it wouldn’t take mush in the way of green house gasses to make that sea level rise a lot. Thus amplifying the effect of global warming caused my the burring of fossil fuels.
“So, right now the ocean levels are at their lowest point in all of the last 540 million years.”
That is not true. If you look at the graph from NOAA, below, you will see that the oceans were about 120 meters lower during the peak of the last glaciation:
https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcT9ApOquS5boN8JB1R2aVnmrEbtOINm7UlrrZ7jLEliaX02mWRaWvMUCQqlXl2eN9Ecow4&usqp=CAU
Note also that unlike the NOAA graph, the graph above, provided by the authors of this study, does not provide associated uncertainties (margin of error) for their work. The uncertainty should increase as one goes back in time. Thus, sea level may well have been even lower during one of the past Ice House events, such as the Carboniferous. Figure 5 from their published paper suggests that is was much colder during the Ordovician-Silurian transition than what it has been during the Pleistocene-Recent time. We just don’t know because the uncertainty envelope for the data in this study is not provided.
Interesting that there was a vast southern ice-cap during hot, swampy, giant-dragonfly Carboniferous times when I have been led to understand that atmospheric CO2 reached the giddy concentration of 4550ppm, as opposed to 450 or so ppm to- day. Ok; the Carboniferous lasted about 70 million years so there is plenty of time for apparently contrary stuff to have gone on, but it would be nice to have more precision in description of the timing of such contrary stuff, even in a popular type of publication such as SciTech Daily. ‘Twould save me time in digging out dry and dusty learned academic journals when I have better stuff on which to spend my few years left to me.