The land beneath our feet may have been shaped by forces beyond the solar system. According to a recent study published in the journal Geology, the early solar system surfed through the four major spiral arms of the Milky Way and caused major growth spurts. There was a rain of comets on Earth as a result of the large impacts of the galactic passages.

The continental crust, where the majority of Earth's biomass is, has a potentially fundamental connection to the universe.

The timing of comet impacts via trace crystals and tiny glass beads in the ground has been proven by the theory. It has received support from other geologists, but has also received criticism for ignoring simpler explanations. The astronomer have holes in the theory.

The study does not cover the entire scale of the Milky Way. Blocks of crust from the earliest part of the Earth's history can be found in Australia and Greenland. They were trapped within a melted blob that gushed onto the surface and hardened into a new crust before they traveled upward. The crystals kept a detailed record of their birth. Scientists can use the elements that are trapped within them to track age. There are other elements in the crystals.

During a period of 3.8 billion to 2.8 billion years ago, magma punctured the surface and built new crust every 170 million to 200 million years. The pattern is similar to the rate at which Earth passes through the galaxy. The scale would be imprinted on Earth.

As the solar system moves into a spiral arm, the stellar density in the arm's comets will increase, which will cause the Oort cloud to disappear. Tim Johnson, a co-author of the paper, said that the rocky bit on top acted like a champagne cork. The mantle's melting point was lowered when the pressure dropped. The basalt looked a lot like the dark rocks in Hawaii or Iceland. The base of the basalt was so thick that it melted and formed granite, a pale colored rock that floats on top of everything else.

There is evidence for the theory in the spherule beds. When a comet strikes Earth, the hot particles that were blasted into the atmosphere coalesce into molten rain and form a layer of small glass beads. The solar system moved into a spiral arm when the two spherule beds were around 3.25 billion years ago.

Brendan Murphy was not involved in the study, but he said it was a great insight. It has made me think about the early Earth in a different way.

Some scientists are not sure. Ross Mitchell, a scientist at the Chinese Academy of Sciences, was not involved in the study. There are only two spherule beds that match the data, and one of them is not located in Australia, meaning that the timing may not match after all. The paper is shaky because of that. He says trying to build a house on the Mississippi Delta is similar to that. Maybe it lasts for a month when people read your paper, but a year or two from now, that foundation could be in trouble.

Mitchell objects to scientists entertaining extraordinary ideas until they rule out the boring ideas. He has a boring explanation for the regular movements of the plates that make up the planet. The amount of time it takes for a slab of crust to travel from the surface to the core-mantle boundary is 170 million to 200 million years. When other material moves up as slabs sink, it's likely that the mantle will melt and create new crust. Is it really necessary to go to the outer reaches of the universe if we already have ready-made explanations from Earth's own cycles? Mitchell wants to know what's going on.

There is a comeback byKirkland. The planet was too hot and the mantle was moving too fast for it to sink all the way down to the core-mantle boundary, according to him. Murphy agrees that the origin of subduction is a contentious topic and that many researchers think it got a later start. Bombardments were taking place early on. The solar system's early history was a shooting gallery according to him.

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One of the controversial aspects of the theory is the claim that the shooting gallery had comets in it. There is a lot of energy that comes from the outer reaches of the solar system. Scientists don't see a lot of evidence for cometary impacts. The more typical incoming objects are asteroids. Margaret Landis is a planetary scientist at the University of Colorado Boulder who was not involved in the study.

Bill Bottke agrees that comet showers are rare. The comets are not likely to hit Earth. It is true that comet showers can be triggered by passing stars thatperturb the inner Oort cloud, but they are very rare, even during a spiral arm passage. It is worth beingambitious but notambitious to the point where you push the data beyond what is reliable.

Johnson said he has received a number of e-mails from geologists that were not nice. Messages of support have also been sent to him. Some people who prefer the status quo will be upset by these things. That is exactly how science progresses. Murphy agrees that the paper will encourage people to look at the data in a different way. He says it certainly has his attention. I am certain that is the case for anyone who is reading this paper. That is a major contribution regardless of whether or not it is correct.