Studying the boundary between the Earth’s core and mantle, geophysicists have found that it is not as smooth as previously thought. Surfaces separating the inner layers also have a complex relief. It turns out that our planet is not at all like a set of spheres nested into each other, as is customary to portray it.

Reading the waves. Earth’s crust

The deep bowels of geophysics are judged by seismic waves generated by earthquakes. There are longitudinal P-waves – when elastic mechanical vibrations occur along the propagation direction and transverse S-waves – the vibrations in them are perpendicular.At the boundary of layers with different densities, the wave velocity changes dramatically. In the transition from a solid crust to a more plastic upper mantle, it increases. This border is called the surface of Mokhorovichich. The lower mantle is harder than the upper. The outer core, in which transverse seismic waves do not propagate, is liquid, and the inner core is again solid, but slightly plastic.

While the network of seismographs was rare, the sections between the inner shells with a certain degree of conventionality were depicted as spheres. As the data accumulated, it became clear that each of these boundaries is a complex surface with its relief and internal “mountains” even higher than on the Earth’s surface, and the “troughs” are deeper. From the top of Everest to the bottom of the Mariana Trench about 20 kilometers, and, for example, the differences of the border of Mokhorovichich, dividing the crust and upper mantle, reach 40 kilometers. And all this at a depth of five to 70 kilometers.

This was proved by scientists from China and the United States . They analyzed the results of observations of hundreds of seismic stations obtained from the same events: the earthquakes in Bolivia of 1994 and the Sea of ​​Okhotsk in 2008 and 2012, as well as archival records of seismographs of the National Center for Information on Earthquakes of the US Geological Survey.

The authors of the study found that for the boundary between the upper and lower mantle, located at a depth of about 660-670 kilometers, the data of the various stations almost completely coincide. That is, she has a stable relief, which she even managed to map. Signal processing of the Bolivian earthquake made it possible to literally create a “topographic map” of the surface of the lower mantle for an entire region in Southeast Asia .

The most dynamic area. Mantle and core

When talking about the dynamics of the Earth, they usually mean large-scale surface processes associated with the movement of lithospheric plates. In the zones of mid-ocean ridges and rifts, the lithosphere moves apart, and in subduction zones on the outskirts of the continents, oceanic plates sink under the continental.

But no less dynamic processes and surface movements occur inside the Earth – only their reflection. First of all, we are talking about mantle convection, which arises due to the temperature difference in the bowels and on the surface of the planet. 

Upward flows of convection cells stretch the lithosphere, downward flows drag it into the mantle. Moreover, in the upper parts of the cells, the substance flows in a horizontal plane and these flows cause lithospheric plates to move.The most dynamic region of the Earth is located on the border of the core and mantle, at a depth of about 2900 kilometers.

It is believed that its heterogeneity affects many geological processes, in particular, the oscillation of the axis of rotation of the Earth and the characteristics of the geomagnetic field. In addition, convection itself is a consequence of what happens in the D ”layer at the boundary with the core.On its surface, scientists discovered arrays of unusually dense, hot rocks – zones of abnormally low seismic wave velocities (ULVZ – Ultra-low velocity zones). They stretch for hundreds of kilometers, and their “height” – tens of kilometers.Above them are hot spots with volcanoes: Hawaiian, Marquesas, Galapagos Islands and the Samoa archipelago in the Pacific Ocean, Canary Islands and Azores , Iceland in the Atlantic, Kerguelen archipelago in the Indian, Afar volcanism zone in the Great African Rift.

Using the new machine learning algorithm, American scientists at Johns Hopkins University and the University of Maryland at College Park together with their Israeli colleagues from Tel Aviv University performed a parallel analysis of seven thousand seismograms covering hundreds of earthquakes from 1990 to 2018, and for the first time compiled a detailed section map the core and mantle of the Pacific region, on which all ULVZ zones were applied.It turned out that ULVZ are only separate protrusions within the larger, low-shear-velocity provinces (LLSVP) provinces, which are also called superplumes. Their branches penetrate up into the mantle for thousands of kilometers. Now scientists distinguish two such provinces – African and Pacific.

The circulation of matter in the mantle

Australian scientists from the University of Curtin suggested that the periods when all the land of the Earth united into single supercontinents – Pangea, Rodinia, Colombia and others, coincided with activity in the deep LLSVP provinces. They built a dynamic model linking the evolution of superplumes to the assembly and decay of supercontinent. According to this model, LLSVP arrays are formed from lithospheric plates, which, as it turned out, sinking, does not dissolve in the mantle, as previously thought, but descend to the very boundary of the core. Here they melt, and giant drops of preheated matter – mantle plumes – coming off from LLSVP, float to the surface, giving rise to a new geodynamic cycle. The lithosphere rises above the plumes, forming a dome, and then cracks and diverges.

Inside the core

Researchers from the US and China have analyzed how seismic waves passing through the boundary between the outer and inner core change. For this, we used signals from doublets – repeated earthquakes with the same epicenter.

It turned out that these changes have a certain periodicity, which can be explained by two mechanisms: either the inner core rotates by about 0.05-0.1 degrees per year, or high “mountains” and deep “canyons” appear on its surface. So, a dynamically changing relief can also be at the deepest boundary between the earth’s shells.

The Earth’s magnetic field has been quiet lately. Very quiet. The sun is in a deep minimum of activity, which may be the deepest solar minimum in a century. 

Geomagnetic storms simply do not exist. But on June 23, something unusual was recorded. The Earth’s magnetic field swung back and forth by about 1/3 of a degree.

“That’s why I was so surprised on June 23 when my instruments detected a magnetic anomaly,” said Stuart Green, who works with a research-class magnetometer in his home in Preston, UK. 

“For more than 30 minutes, the local magnetic field oscillated like a sine wave.”

Green quickly checked the solar wind data from the NOAA DSCOVR satellite. 

“There was nothing – no surge in solar wind speed or other factors that could explain this disturbance,” he says.

He was not the only one to notice this. In the Lofoten Islands of Norway, Rob Stams found a similar anomaly on his magnetometer. 

“It was amazing,” says Stams. “Our magnetic field swung back and forth by about 1/3 of a degree.” I also discovered ground currents with the same 10 minute period.”

Space physicists call this phenomenon “pulsation.” Imagine that you are blowing on a piece of paper, making it flutter from your breath. Solar wind can have a similar effect on magnetic fields. During the extreme silence of the solar minimum, such waves can be “heard” like a pin falling in a quiet room.

The Earth’s magnetic field was so quiet on June 23 that this ripple was heard all over the world. The INTERMAGNET global network of magnetic observatories recorded wave activity simultaneously from Hawaii to China and the Arctic Circle and even in Antarctica.

PC waves are classified into 5 types depending on their period. The 10-minute wave June 23 falls into the Pc5 category. Slow Pc5 waves were associated with the loss of particles from Van Allen’s radiation belts. Energy electrons beat these waves down into the Earth’s atmosphere, where they scatter.

When Taku Suganuma pulled his fishing net off the coast of Imizu, he caught a catch he had never seen before. The strange fish had an unusual head and a silver body one meter long.

Suganuma, 24, caught fish on a Shintokumaru fishing boat, which sailed from Imizu when the squid fishing season was drawing to a close.

At first, he thought it was the Lowseil river fish, which is often caught on the net this season. However, a younger colleague, who knows about the species of fish, said that it could be a deep-sea North Pacific cuttlefish, aka a unicorn.

Suganuma decided to give the fish to the Wozu aquarium because of its rarity. North Pacific cuttlefish was delivered to a fishing vessel in Toyama Bay off the coast of Imizu.

According to records stored in the aquarium, North Pacific cuttlefish fish have not been seen in Toyama Prefecture for more than 30 years since one of them was found ashore at the mouth of the Katakaigawa River in Ouza in 1988. However, eight of the unicorns were either caught or hit the net from February to April last year.

The North Pacific cuttlefish is characterized by a red dorsal fin and releases black ink from its anus in response to danger.

It is believed that the fish lives in the intermediate layer at depths of 200 to 1000 meters from the coast, but details about its life remain unknown, because it is rarely caught.

Samples usually die quickly due to differences in water temperature and other factors when they are brought to the surface. Only one of the eight fish taken to the aquarium survived for about an hour.

It released a large amount of ink several times as it sailed in a large tank containing 16 tons of sea water, instantly limiting visibility to only 10 centimeters in advance.

Tomoharu Kimura, the owner of the aquarium, said the white flesh of the fish crunches like a flounder when served as sashimi, while it has a soft and simple taste.

A close look at the contents of its stomach gave a hint of life and the ecosystem of the North Pacific cuttlefish fish, as well as a threat to marine life: plastic waste.