About the project

About Past Earths

One slider from 540 million years ago to today, on a 3D globe drawn from published reconstructions of Earth’s past.

Past Earths is a personal, non-commercial science visualisation. Drag the slider and the continents drift, seas flood and drain, and ice sheets grow and melt. It joins three very different kinds of reconstruction into one timeline, so the further back you go, the rougher the picture gets.

Three kinds of map

Detailed: the last 80,000 years. Today’s land and sea floor, from NOAA’s ETOPO 2022 relief model, with the ice sheets and sea level of the PaleoMIST reconstruction every 2,500 years. Sea level is worked out place by place: the global fall as water was locked up in ice, plus the crust sinking under the weight of the ice sheets and rising again after they melted. That’s why the sea floods into Hudson Bay and the Baltic as the ice retreats. Between snapshots, the ice margins move smoothly from one to the next. The readout’s sea level is the average over the ocean of the time. Today’s lakes, from HydroLAKES, fill in between 12,000 and 8,000 years ago as the ice clears; they are today’s shorelines, not those of the time.

Approximate: 5 million to 80,000 years ago. Today’s land at the global sea level of the time, from ocean-sediment records. The ice sheets of this stretch aren’t reconstructed here yet, so the globe shows today’s ice, and the crust’s sinking under past ice is left out. Sea level is averaged over each step, so the shortest swings are smoothed away; during the Last Interglacial, for example, this curve stays near today’s level where coral reefs suggest the sea stood several metres higher. Between 5 and 3 million years ago the last deep-time map gives way to today’s, the continents sliding along with their plates to where they are now, so coasts there are a blend of the two.

Schematic: 540 to 5 million years ago. Christopher Scotese and Nicky Wright’s PALEOMAP paleo-elevation maps, one every 5 million years. They are expert reconstructions of where continents, seas and mountains were, not surveys, and they are smoothed to about 1°: read them for the big picture, not the shape of a coastline. Between two maps the globe morphs one into the next, carrying each continent along with its tectonic plate (from the same PALEOMAP plate model), so continents drift and coasts and ice move gradually rather than jumping every 5 million years; it can’t zoom in as far. Heights are relative to that era’s own sea, so there is no single sea-level number to compare with today’s. The finer texture (hills, ridges, the bays, inlets and islands along the coasts, and the patchwork of forest and desert) is drawn procedurally to suggest a real landscape; it isn’t in the data, so read a deep-time coast’s small features as a plausible guess. The maps of the last 25 million years lean more and more on today’s own ground instead, keeping only what Scotese changed since today, so by 5 million years ago Britain is Britain, still joined to the continent where he has it so; the changes he drew finer than about 1° aren’t in his maps to keep.

Every age is drawn in the same painted style, today included: colours come from height, latitude and slope, with deserts in the subtropics, tundra and snow towards the poles, and bare rock and dust before land plants spread, about 430 to 380 million years ago. There is no satellite imagery anywhere, so today looks like every other age.

Ice through deep time

Deep-time ice comes from Cao and colleagues’ digitisation of Golonka’s paleogeographic maps, which gives the ice of ten intervals between 380 million and 2 million years ago. Those outlines are tied to today’s continents, so each piece is carried with its PALEOMAP plate to the time of the map, which puts it on the continents the elevation maps draw. The ice surfaces are schematic domes, showing where ice was rather than how thick it was.

Two choices are worth knowing. The Late Ordovician and early Silurian glaciation (about 450 to 440 million years ago) is older than Cao’s maps, so it’s drawn as a polar ice cap over the land near the South Pole. And Golonka’s 81 to 58 million year map, which shows ice in what is generally thought a hothouse world, is left out: Antarctica’s lasting ice sheet dates from about 34 million years ago.

Where was I?

Drop a pin on today’s Earth, at your own location or anywhere you tap, and it rides its tectonic plate through deep time. The motion comes from the PALEOMAP plate model, the same one the deep-time maps are drawn with, so the pin stays on the continent on screen. Where the crust under the pin is younger than the age on screen, the pin fades and says so. Your location is used only in your browser to place the pin; it isn’t sent anywhere.

Moments

Sources and credits

• Scotese, C.R. & Wright, N.M. (2018). PALEOMAP Paleodigital Elevation Models (PaleoDEMs) for the Phanerozoic. doi.org/10.5281/zenodo.5460860. CC BY 4.0. The deep-time elevation maps.
• Scotese, C.R. (2016). PALEOMAP PaleoAtlas for GPlates and the PaleoData Plotter Program. EarthByte. The plate model (rotations and plate polygons) that moves ice and pins.
• Cao, W., Zahirovic, S., Flament, N., Williams, S., Golonka, J. & Müller, R.D. (2017). Improving global paleogeography since the late Paleozoic using paleobiology. Biogeosciences 14, 5425–5439. doi.org/10.5194/bg-14-5425-2017. CC BY 4.0. Deep-time ice, after Golonka (2006).
• Gowan, E.J. et al. (2021). A new global ice sheet reconstruction for the past 80 000 years. Nature Communications 12, 1199. Data: doi.org/10.1594/PANGAEA.905800. CC BY 4.0. Ice sheets and sea level of the last 80,000 years (PaleoMIST 1.0).
• Spratt, R.M. & Lisiecki, L.E. (2016). A Late Pleistocene sea level stack. Climate of the Past 12, 1079–1092. Data: NOAA NCEI Paleoclimatology. Sea level to 800,000 years ago.
• de Boer, B., Lourens, L.J. & van de Wal, R.S.W. (2014). Persistent 400,000-year variability of Antarctic ice volume and the carbon cycle is revealed throughout the Plio-Pleistocene. Nature Communications 5, 2999. Data: doi.org/10.25921/xs31-nt56. An ice-sheet model forced by ocean-sediment records; sea level from 800,000 to 5 million years ago.
• NOAA National Centers for Environmental Information (2022). ETOPO 2022 15, 30 and 60 Arc-Second Global Relief Model. doi.org/10.25921/fd45-gt74. Public domain. Today’s land and sea floor.
• Messager, M.L., Lehner, B., Grill, G., Nedeva, I. & Schmitt, O. (2016). Estimating the volume and age of water stored in global lakes using a geo-statistical approach. Nature Communications 7, 13603. doi.org/10.1038/ncomms13603. Data: HydroLAKES, CC BY 4.0. Today’s lakes and reservoirs.
• Natural Earth land polygons and playas (public domain), used to separate land from sea in today’s map and to tell dry salt pans from lakes.
• Geological periods follow the International Commission on Stratigraphy’s chart. Plate reconstructions were computed with pyGPlates.

The data preparation is open: the scripts that turn these sources into the globe’s maps are in the project’s source code.

Caveats

• Deep-time maps are reconstructions with real uncertainty, especially before about 250 million years ago, where little ocean floor survives to check them against.
• The three kinds of map meet at 5 million and 80,000 years ago; crossing either point changes what the globe can show, and deep time’s closest zoom lasts until today’s map has taken over, 3 million years ago.
• Relief is exaggerated about 40 times when zoomed out, so mountains and ice sheets read from orbit.
• Up close, ice edges are drawn finer than any reconstruction records them: the ragged lobes, ice reaching down valleys, rock showing through thin ice, the grey bare ice and meltwater near the margin and the moraine beyond it are drawn procedurally, guided by the terrain. The outlines they follow are the data’s.
• Sea level is the mean level; tides and storms are not modelled.
• Lakes are today’s, filling in from 12,000 years ago; the giant meltwater lakes along the retreating ice sheets aren’t drawn. Where a lake’s depth hasn’t been surveyed, its colour is a guess from its size and average depth. Salt pans that are dry most years, like Lake Eyre and Salar de Uyuni, are drawn as land.

About the author

Past Earths is a hobby project by Richard Franklin, a sibling to Sliding Shores. Corrections and suggestions are very welcome at [email protected].