Guest “truth is stranger than friction” by David Middleton

Alternate Title: The Cretaceous Sea Level Paradox

Oceans are at their deepest in 250 million years
And they have hardly been deeper in the last 400 million years than now.

Lasse Biørnstad
JOURNALIST
PUBLISHED Monday 08. june 2020 – 12:24
“It moves absurdly slowly,” says Krister Karlsen. He is a PhD candidate in Geophysics at the University of Oslo (UiO)’s Centre for Earth Evolution and Dynamics.

Karlsen is talking about how the Earth’s tectonic plates move – ever so slowly but surely, every single year. From a human perspective, this happens so slowly that it is almost imperceptible.

[…]

The world map 200 million years ago shows all the continents assembled in the supercontinent of Pangaea, a time when dinosaurs were well on their way to dominating the Earth’s landmasses.

Since then, the continents have been shifting farther and farther apart, and now they may be as far apart as they can be, says Karlsen. Give the Earth a few hundred million years more, and the continents will probably remerge into a new supercontinent. One proposed name for that possible future reunion is Pangaea Proxima, according to New Scientist.

The movements and age of tectonic plates have a great effect on the depth of the world’s oceans. Just over 100 million years ago, the oceans were around 250 metres shallower on average than they are today.

The older the seabed, the deeper it is, according to a new research article by Karlsen and several colleagues at the Centre for Earth’s Evolution and Dynamics.

[…]

Science Norway

Karlsen et al., 2020 is essentially a reconstruction of plate tectonics and the age of the oceanic crust over time.

According to their reconstruction (and others), 100 million years ago, during the middle of the Cretaceous Period, the oceans were about 250 meters shallower than they are today *and* sea level was about 250 meters higher than it is today. Process that for a moment… The oceans were 250 meters shallower, but the water level was 250 meters higher than it is today. This was due to the geometry and distribution of the ocean basins. While advancing and retreating ice sheets may have played a role in Cretaceous marine transgressions and regressions, the Cretaceous sea level paradox was a tectonic feature and a boon to humanity.

During the Mid-Cretaceous, shallow seas covered many continental interiors…

While the ocean basins were, on average, considerably shallower than they are today.

“How about that, geology fans?”

Apollo 15 CapCom Joe Allen on Dave Scott’s discovery of the “Genesis Rock.”

References

Goswami, A.; Hinnov, L.; Gnanadesikan, A.; Young, T. Realistic Paleobathymetry of the Cenomanian–Turonian (94 Ma) Boundary Global Ocean. Geosciences 2018, 8, 21.

Karlsen, Krister S., Mathew Domeier, Carmen Gaina, Clinton P. Conrad,
A tracer-based algorithm for automatic generation of seafloor age grids from plate tectonic reconstructions, Computers & Geosciences, Volume 140, 2020, 104508, ISSN 0098-3004, https://ift.tt/3cQSfpA.