Astrophysicist Xiaolei Zhang from George Mason University (USA) presented an article in which he proves that the collapse of the supercontinent Rodinia is caused by an indirect collision of the Earth and an alien planet the size of Mars. The scientist questions the theory of continental drift and gives arguments in favor of his version.
In the 19th and first half of the 20th century, it was believed among geologists that the Earth resembles a baked apple, which gradually cools and shrinks, and "wrinkles" appear on its surface. On the basis of the “apple hypothesis”, the theory of geosynclines arose, according to which individual parts of the earth's crust descend and then rise, forming mountain ranges. However, as early as 1912, geophysicist Alfred Wegener challenged this scheme, suggesting that mountain building is due to continental continental drift. In favor of his version, he cited the argument that the outlines of the west coast of Africa and the east coast of South America coincide, as if these continents were part of one supercontinent.
At the time, it was a rather daring idea that challenged conventional scientific ideas. Unsurprisingly, Wegener's assumption was rejected. It is possible to understand skeptical scientists: Wegener could not explain what exactly caused the continental drift, and their outlines could be a coincidence. Nevertheless, Wegener had followers who were looking for more compelling arguments for continental drift.
In 1960, a spreading hypothesis was put forward, according to which, in the region of mid-oceanic ridges, mantle flows rise to the earth's crust, forming a new bottom and pushing old rocks apart. Thus, the lithospheric oceanic plates are somewhat reminiscent of tractor caterpillars. In one place, the crust rises, floats over the mantle, and sinks in another place (subduction zone). This hypothesis was confirmed when stripe magnetic anomalies were discovered in the oceanic crust - a sequence of "records" about periodic changes in the direction of the Earth's magnetic field. Moreover, the further from the ridge the "strip" of residual magnetization was located, the more ancient it was.
In the subduction zones, the continental crust also builds up, under which the oceanic crust sinks. However, if two continental plates collide, then no sinking occurs; instead, high mountain systems like the Himalayas are formed.
Subduction zone diagram / Photo: Yug / Wikimedia
Why do mantle flows rise in the region of the ridges, and fall in the subduction zone? The answer to this is mantle convection. Closer to the core, the melt has a high temperature, as a result of which it rises to the crust. In its place comes a cold mantle, which has already given off heat to the lithosphere. These rising and falling currents are closed to form cells. At the top of each cell, the mantle moves horizontally, causing the slabs to move in the same direction. The force of this mechanism is sufficient to cause the continent to split, when parts of it begin to shift in different directions.
Some scientists, including astrophysicist Xiaolei Zhang, have proposed another possible mechanism for the continental shift. In their opinion, a large asteroid or comet fell to Earth. This can explain the sharp change in the direction of the Hawaiian Ridge, for example. In addition, convective cells, according to Zhang, cannot ensure long-term stability of hot spots - areas in which active volcanic activity occurs. The scientist also questions the subduction mechanism of the formation of the Rocky Mountains - a ridge located in the western United States and Canada.
Promotional video:
To cause a continental shift, the object that fell to Earth had to be the size of Mars. Zhang believes that the impact of a small wanderer planet occurred about 750 million years ago and fell on the territory where the Colorado Plateau (western USA) is now located. The cataclysm led to the split of the supercontinent Rodinia, which arose 1.1 billion years ago. The resulting crater was comparable in size to the Colorado plateau itself, whose area reaches 337 thousand square kilometers. For comparison: the area of the Chicxulub crater, formed during the fall of a ten-kilometer asteroid that killed the dinosaurs, is 25 thousand square kilometers.
Where did the wanderer planet come from? 4.5 billion years ago, another planet, Theia, probably collided with the Earth. It is believed that this disaster led to the formation of the moon. Theia was formed at the Lagrange point, which was located almost directly in the Earth's orbit, but for a long time kept at a distance from our planet. If the solar system consisted only of the Sun, Earth and Theia, the collision would not have happened, but the gravitational influence of other planets displaced Theia from its place and threw it towards the Earth. But 750 million years ago, the second Theia could no longer exist - the planets of the solar system were firmly established in stable orbits.
Supercontinent Rodinia / Photo: Kelvin Ma / Wikimedia
Zhang believes the wanderer planet came from another system. This can happen when the solar system, orbiting the center of the Milky Way, passes through galactic arms - structures with a high density of stars, gas and dust. This concentration of matter leads to the appearance of large stars, whose life ends in a supernova explosion. Explosions can rip off exoplanets from their homes, sending them towards the Sun.
As an argument in favor of his hypothesis, Zhang cites the unusual geological structure of the plateau in Colorado. For example, layers of rocks that formed about 750 million years ago form an anomaly called the Great Unconformity. They do not lie in a strict stratigraphic sequence (older layers are at the bottom, younger ones are at the top), but form a chaotic picture, as if something had severely deformed them. There are also rocks of the Precambrian times, unique for the plateau, which underwent melting and metamorphism.
The scientist also drew attention to the fact that the periods between the intersections of the solar system of the arms of the galaxy coincide with the intervals between mass extinctions on Earth within the Phanerozoic eon (which includes the Paleozoic, Mesozoic and Cenozoic eras) and the splits of supercontinents.
It should be remembered that Zhang's hypothesis is so far only the hypothesis of one scientist. So far there is no serious evidence that the already formed Earth in the relatively recent geological past could survive the impact of a wanderer planet. The same Great Disagreement can be explained by the washing out of the upper layers by the waters of the sea, periodically advancing on the North American continent during the Early Cambrian. This erosion process has been linked to the Cambrian Explosion, when calcium and other minerals were washed into the ocean, altering the water chemistry and creating skeletal marine life. A global cataclysm, which would turn the entire planet into a flaming ball, does not fit well with the already known picture of geological and biological evolution.
According to Zhang's logic, tei-like planets must fall at an enviable frequency in order to push the continents apart. So far, his hypothesis provides more questions than answers. At one time, Wegener's theory of continental drift, hastily rejected by the world community, was much more understandable and justified.
Alexander Enikeev
