What’s under the crust?

No this isn’t about pies I read an interesting account about the earth’s deep blobs, the size of continents, that sit in the lower mantle of the earth, which is just above the earth’s core.  This mantle is a layer of abundant rocks and dry oceans.  The rocks are interspersed with a kaleidoscope of crystals, from diamonds. They survive under immense pressures that if they could be brought to the earth’s surface would break up.  In addition to the rocks is an “ocean” which doesn’t contain any liquid; the water being trapped within the mineral olivine.

The rocks are mainly bridgmanite and davemaoite.  Bridgmanite has also been found in minute quantities in meteorites and US geologists have found tiny amounts of davemaoite in a diamond from the Orapa kimberlite pipe in Botswana,

Davemaoite was the name given to honour the prominent experimental high-pressure geophysicist Ho-kwang (Dave) Mao.  Bridgmanite is named in honour of the physicist Percy Bridgman.  It is  the most abundant mineral in the lower mantle of the earth.

These elusive minerals can only be seen in their natural form when they become trapped inside diamonds brought to the surface. Even then, what these crystals would actually look like deep inside the Earth is impossible to predict, because their physical properties are so altered by the pressures they usually exist under.

Understanding the blobs could help to unravel some of geology’s most enduring mysteries, such as how the Earth formed, the ultimate fate of the “ghost” planet Theia, and the inexplicable presence of volcanoes in certain locations around the globe. They may even shed light on the ways the Earth is likely to change over the coming millennia.

The Russians embarked on an ambitious exploration into the earth and in 24 years had reached some 12,000m underground until the drill became stuck as the granite ceased to be drillable due to the intense heat of the earth’s interior.  

Even using seismic instruments and methods geologists have a lot to discover about the structure and composition of the earth’s inner mantle.

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Looking at a map of Earth today may appear differently in the future.

Geologists know that supercontinents disperse and assemble in cycles: we’re halfway through one now. So, what kind of supercontinent might lie in Earth’s future? How will the landmasses as we know them rearrange over the very long-term? It turns out that there are at least four different trajectories that could lie ahead.

Earthquakes of this scale usually happen on or near major subduction zones, where oceanic plates plunge beneath the continents and are melted and consumed in the hot mantle. They involve collision and destruction. The 1755 quake, however, happened along a “passive” boundary, where the ocean plate underlying the Atlantic transitions smoothly into the continents of Europe and Africa.

Joao Duarte, a geologist at the University of Lisbon, realised that, if this happens, it could lead to the Atlantic eventually closing. And if the Pacific continued to close too – which is already occurring along the sub-ducting “Ring of Fire” circling it ­– a new supercontinent would eventually form. He named it Aurica, named because the former landmasses of Australia and the Americas would sit at its centre.

The four scenarios

He combined with another geologist Hannah Davies, and oceanographer Matthias Green at Bangor University. Their work led to four scenarios. They then collaborated with Michael Way, a physicist at the Nasa Goddard Institute for Space Studies. Way’s modelling of the supercontinent climates – which took months using a supercomputer – revealed some striking variations between  the four scenarios.

This modelling is speculative, and there may be unanticipated geological surprises that change the outcome. However, what can be said for certain is that the landmasses we take for granted will one day rearrange into an entirely new configuration. Countries once isolated from one another will be close neighbours.

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Star Wars fan especially of Yoda.

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