Update on the Oblate Spheroid

A correspondent sent me a link to THIS MAGAZINE ARTICLE. This, in turn, is based on THIS ACADEMIC PAPER. The articles are concerned with the shape of the Earth and the changes which are taking place to it.

When I went to University I was much interested in this and was amused to find that the north to south flowing Mississippi had its source closer to the centre of the Earth than its mouth, so it was flowing uphill!

But the author of the scientific paper has gone rather further into the problem than I did and has found that global warming is the cause - and it is accelerating. Ice has been removed from the poles so the Earths surface has risen. Meanwhile the melt water has moved to lower latitudes and depressed the Earth's surface. The rocky spheroid is becoming less oblate.

But the affect on the Earth's gravity is the opposite. Moving mass (water) to the equator makes the gravitational geoid more oblate!

I found this difficult to comprehend so used Google Gemini to summarise the academic paper - (this is long and very dense) - and it came up with this:-

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Summary of Mapping Global GNSS Vertical Velocities to Solid Earth Figure Change (Kotsakis, 2026)

A 2026 study published in the Journal of Geophysical Research: Solid Earth reveals that the physical shape of our planet is changing at an accelerating pace.

Earth is not a perfect sphere; it bulges slightly at the equator due to its rotation. However, using precise Global Navigation Satellite System (GNSS) tracking stations, geologist Christopher Kotsakis analyzed movement across Earth’s crust between 1997 and 2015. The findings show a clear global pattern: the polar landmasses are rising (uplift), while regions near the equator are sinking (subsidence). This ongoing movement means the solid surface of the Earth is gradually becoming slightly rounder and less flattened at the poles.

Between 1997 and 2000, polar regions were rising at a rate of roughly 0.5 millimeters per year. By 2015, that speed had doubled to about 1 millimeter per year, demonstrating an overall acceleration in surface deformation.

The primary driver behind this shift is the redistribution of water mass across the planet, largely fueled by climate change. As ice sheets and glaciers in places like Greenland and Antarctica melt, the immense weight pressing down on the polar crust lightens. Consequently, the rocky ground underneath springs back up (elastic rebound).

At the same time, all that melted ice flows into the global ocean network, adding heavy water weight to lower latitudes and causing the seafloor and equatorial regions to sink under the new load.

Interestingly, this creates a subtle paradox between Earth's physical ground and its gravitational field. While the rocky crust itself is becoming slightly rounder, the mass of water collecting around lower latitudes causes the planet's gravitational field to remain flattened. Overall, the study highlights how dynamic Earth's solid surface is in response to shifting climate and ocean dynamics.

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 Geol Soc Nightschool

Want to find all about dinosaurs? Then go to THIS WEBSITE and let Mike Benton tell you all he knows - or at least quite a lot!

This a new venture by the Geol Soc. It will be live at 17:30 on the 21st October and will last for about 2 hours. It will not be recorded so you need to be online.

If you go to the link above you will find not only Mike Benton but lots of other educators teaching lots of geological topics. This should fill up your calendar until almost Christmas!

Deep Down, Its Complicated

A correspondent forwarded THIS LINK which is based on THIS JOURNAL ARTICLE. It concerns seismic waves created by the French nuclear tests in the South Pacific between 1977 and 1995. The records used were recorded in Kazakhstan. 

One would think that seismic waves created in one spot and recorded in another would be the same over time. After all they are travelling through the same stuff!

But no! Using waves which reflected inside the (liquid) outer core, the travel times varied over time. This leads to the conclusion that the outer core is dynamically changing. 

This is important as the outer core is responsible for generating the Earths magnetic field.

Both articles are quite complex but Google Gemini is able to give a fairly simple version of the papers. Here it is:-

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A research study published in the Journal of Geophysical Research: Solid Earth (doi: 10.1029/2026JB033798) reveals that the deep interior of our planet is far more dynamic than long believed, challenging the traditional view that Earth’s outer core is a uniform, static ocean of liquid metal.

Led by Virginia Tech geophysicist Ying Zhou, researchers analyzed seismic data recorded during underground nuclear tests conducted by France at Moruroa Atoll in French Polynesia between 1977 and 1995. Subterranean nuclear explosions provide a unique advantage over natural earthquakes for geoscientists: because test detonations occurred at precisely known, nearly identical locations, they generated consistent seismic wave pathways through Earth’s deep interior. By analyzing 112 pairs of historic explosions, the team tracked microscopic variations in how long it took specific waves (known as PKrKP waves, which reflect within the outer core) to travel through the planet over several decades.

The findings indicate that the travel times of these deep-reaching waves changed measurably between test events. This shift points to a massive, previously unrecognized structure drifting within the molten outer core beneath the southern Pacific Ocean. Estimated to stretch roughly 700 kilometers across and 100 kilometers thick, this feature may consist of solid material suspended inside the churning liquid metal or localized density variations drifting as the core circulates.

These rapid, decade-scale shifts are significant because movement within the liquid outer core powers the geodynamo—the planet-wide engine responsible for generating Earth’s protective magnetic field. Understanding that massive structures can shift deep underground over just a few decades offers scientists a dynamic new model for how Earth’s core behaves, while demonstrating how legacy Cold War-era nuclear records can serve as unexpected time capsules for planetary science.

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 Down to Earth Extra September 2026

The September 2026 edition of Down to Earth Extra has been published. You can download it HERE or you can read it below.

 Down to Earth Extra August 2026

The august 2026 edition of Down to Earth Extra has been published. You can down load it HERE or you can read it below.

 Ichthyotitan severnensis - Finding a New Species

I came across this WEB PAGE and from it was directed to THIS ACADEMIC PAPER. The contrast between the styles is extreme but the basis for both is the same. This is the finding of bones from the jawbone of an ichthyosaur and using the finds to describe a huge creature and erect a new species.

The bones were found by a young girl and her father on Blue Anchor Bay in Somerset and the creature is estimated to be 25m long. It was realised that a similar jawbone had been found some time earlier in the same rock layer, at a nearby locale. This was sufficient for a new species to be postulated.

A washed-up Ichthyotitan severnensis carcass on the beach. Credit: Sergey Krasovskiy.

The story of the find shows that amateur geologists can still be important in our science. And it is cheering to note that they both appear among the authors of the academic paper.

The paper has a long description of the find and a discussion about the naming of a new species. And it asks that if you find something similar to contact them! And they would be delighted if you could find a complete specimen of the animal!

 Did Complex Life Appear Because the Magnetic Field was Weak?

Some parts of the history of the Earth's magnetic field are easy to measure. But the strength of the field is not one of them. We have lots of information of the reversals of the polarity of the field and the direction of the magnetism - think of the stripes on the ocean floor and knowing the latitude of when rocks were laid down - but the field strength of the field is harder to come by.

And this is important for the presence of the field is what protects us from deadly cosmic rays. It is very possible that no field = no life.

But some measurements of field strength have been made and one of the interesting things is that it was very low in the Ediacaran. It was a fifteenth of the present value. This and the consequences of this are discussed in THIS ARTICLE.

Did the reduction in magnetic field strength allow more genetic mutation in the single-celled creatures promoting the multi-celled Ediacaran fauna?

The article goes on to discuss the mechanism which affected the field, essentially the formation of the Earth's inner core. The 100 million years this took covers the Ediacaran and the "Cambrian Explosion".

The article gives a pleasing combination of Earth physics and biology. It may even be true!