The interior of the Earth has changed shape much more than we thought

Deep in the Earth below us are two blob the size of continents. One is under Africa, the other under the Pacific Ocean.

The drops have their roots 2,900 km below the surface, almost halfway to the center of the Earth. They are thought to be the birthplace of rising columns of hot rock called “deep mantle plumes” that reach the Earth’s surface.

When these plumes first reach the surface, giant volcanic eruptions occur – the kind that contributed to the extinction of the dinosaurs 65.5 million years ago. Blobs can also control the eruption of a type of rock called kimberlite, which brings diamonds to depths of 120 to 150 km (and in some cases up to around 800 km) on the Earth’s surface.

Scientists have known that blobs have been around for a long time, but how they behaved over Earth’s history is an open question. In new research, we’ve modeled a billion years of geologic history and discovered the drops come together and separate much like continents and supercontinents.

Earth blobs as imaged from seismic data. The African spot is at the top and the Pacific spot at the bottom. Photo credit: Ömer Bodur

Earth blob evolution

The drops are found in the mantle, the thick layer of hot rock between the earth’s crust and its core. The mantle is solid but flows slowly over long timescales. We know the drops are there because they slow down the waves caused by earthquakes, which suggests that the drops are hotter than their surroundings.

Scientists generally agree that the drops are related to the movement of tectonic plates on the Earth’s surface. However, how the drops have changed over Earth’s history intrigued them.

One school of thought has been that current drops have acted as anchors, locked in place for hundreds of millions of years as other rocks move around them. However, we do know that tectonic plates and mantle plumes move over time, and research suggests the shape of the blobs changes.

Our new research shows that Earth’s drops have changed shape and location far more than previously thought. In fact, throughout history they have come together and come apart in much the same way as the continents and supercontinents on the Earth’s surface.

We used Australia National IT infrastructure to run advanced computer simulations of how the Earth’s mantle sank over a billion years.

These models are based on reconstruct the movements of tectonic plates. As the plates push into each other, the ocean floor is pushed between them in a process known as subduction. The cold rock at the bottom of the ocean sinks deeper and deeper into the mantle, and once it reaches a depth of about 2,000 km, it pushes the warm drops away.

The last 200 million years of the Earth’s interior. Hot structures are yellow to red (darker is shallower) and cold structures are blue (darker is deeper).

We found that, just like continents, blobs can fit together – forming “superlobs” like in the current configuration – and break up over time.

A key aspect of our models is that although the drops change position and shape over time, they still match the pattern of volcanic and kimberlite eruptions recorded on the Earth’s surface. This pattern was previously a key argument for blobs as immobile “anchors”.

Strikingly, our models reveal that the African Spot came together just 60 million years ago – contrary to previous suggestions, the Spot could have existed roughly in its current form. nearly ten times longer.

remaining questions

How did the blobs appear? What exactly are they made of? We still don’t know.

The drops may be denser than the surrounding mantle, and as such may consist of material separate from the rest of the mantle. early in earth’s history. This could explain why the mineral composition of the Earth is different from that expected from models based on the composition of meteorites.

Alternatively, the density of the drops could be explained by the accumulation of dense oceanic material from rock blocks pushed down by the movement of tectonic plates.

Regardless of this debate, our work shows that sinking slabs are more likely to transport fragments of continents to the African spot than to the Pacific spot. Interestingly, this result is consistent with recent work suggesting that the source of the mantle plumes from the African Stain contains continental material, whereas the plumes rising from the Pacific Stain do not.

Blob Tracking

While our work addresses fundamental questions about the evolution of our planet, it also has practical applications.

Our models provide a framework to more precisely target the location of minerals associated with mantle upwelling. This includes diamonds brought to the surface by kimberlites which appear to be associated with the drops.

Magmatic sulphide deposits, which are the world’s largest nickel reserves, are also associated with mantle plumes. By helping to target minerals such as nickel (an essential ingredient in lithium-ion batteries and other renewable energy technologies), our models can contribute to the transition to a low-emissions economy.

Nicholas Flamingo is a lecturer and Omer F Bodur is a postdoctoral researcher at the University of Wollongong. Andrew Merdit is a research fellow at the University of Leeds. simon williams is a researcher at Northwest University, Xi’an.

This article first appeared on The conversation.

Betty K. Park