Shulou(Shulou.com)11/24 Report--

This article comes from the official account of Wechat: SF Chinese (ID:kexuejiaodian), author: SF

Due to the rapid solidification of the Martian core, the geological activity has gradually slowed down, and the Martian magnetic field and plate movement have also disappeared. Without the protection of the Martian magnetic field, the solar wind blows away the Martian atmosphere, resulting in low pressure, causing liquid water on the Martian surface to boil at low temperatures and become unstable. Mars thus became a lifeless planet. The latest research has found that the core is also gradually solidifying. So, will Earth repeat the mistakes of Mars?

(by Phil Newell) / / by Colin Stewart (Colin Stuart)

Translation | Li Shijie

Editor | Zhao Jiaming

The earth's core appeared when the earth was just formed. In the early days of the formation of the solar system, there was a protoplanetary disk (protoplanetary disc) in the solar system. Gradually, the matter in the protoplanetary disk, under the action of gravity, formed a planetesimals. Later, these loose rocks and pieces of metal collided with each other, eventually forming planets, including our Earth.

In this process, heavier iron deposits to the center of the earth, and relatively light rocks float up to the earth's surface. Then the earth cools down, the earth's surface forms a crust, while the iron in the earth's core is in a state of melting, which is maintained by the tremendous pressure exerted from the outside of the core.

The core has been solidifying for billions of years, and it has been cooling. "the fluid iron in the outer core slowly cools down and solidifies into a solid, forming the core," said Dan Frost, a seismologist at the University of South Carolina.

The core is still growing at a rate equivalent to 8000 tons of molten iron solidifying every second-a weight equal to the weight of the world's new population every day. Due to cooling and solidification, the heat of the core is lost and transferred to the outer core, which causes strong convection in the molten outer core, thus forming the earth's magnetic field.

How does the kernel grow? However, the latest research shows that the growth of kernel is uneven. Frost's team has begun to monitor this uneven growth pattern taking place in the interior of the earth. But this is not a simple task, because they can only collect relevant data on the surface, and they have no way to know how much the kernel today is larger than yesterday.

To determine how the kernel grows, Frost's team is looking for evidence of material flow within the kernel. When a local seismic wave passes through the core, if its propagation direction is parallel to the earth's axis (roughly north-south), the propagation speed of the local seismic wave will be faster than when the propagation direction is parallel to the equator. Based on this rule, Frost says that the crystals in the core are arranged in a similar direction. And this consistency can be achieved only if there is a material flow within the kernel.

Through their research, they found that the core under the Banda Sea near Indonesia grew faster than the core below Brazil. However, this imbalance will not last forever. "the crystals in the core are pushed to the slower-growing side by gravity, keeping the core spherical." Frost explained, "it is this material flow that forms the crystal arrangement that we have observed."

A new kernel model is proposed. In Frost's study, they assumed that the kernel contained only one kind of crystalline iron. However, in the past, scientists generally believed that there was a clear difference between the outermost layer and the innermost layer of the kernel.

"there is not a sharp transition between the outermost kernel and the innermost kernel, but a smooth transition." Frost believes that such a kernel model is consistent with his latest findings.

However, it also means that many of the mysteries about the earth's solid core remain unanswered. After all, it is less than a hundred years since we knew about the existence of the kernel, and the kernel has existed for billions of years.

Frost proposed a new kernel model and gave a new mode of kernel growth. So the question comes again: do we need to worry about the solidification of the earth's core?

Actually, we don't have to worry. Because the core won't be fully solidified soon. In fact, the growth of solid-state kernels is relatively slow, with only 2mm thickening each year. Although this is very fast in the geological process, it is expected to take 91 billion years if the outer core in the molten state is fully solidified. Before that, the earth had been dried by the sun.

This article is partly adapted from the 2023.08 issue of Science focus-exploring the Earth's Core.

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