The oldest evidence in the history of research on terrestrial magnetism has been discovered dating back 3.7 billion years; Its power is comparable to the position of the sorae portal that exists today in the universe

The Earth is one of the celestial bodies that has its own strong magnetic field. This is an essential element for many creatures that live on Earth.Terrestrial magnetism“It is understood that it has gradually become stronger since the birth of Earth. However, the exact timing is not well known.

A research team led by Clare I. O. Nichols of the Massachusetts Institute of Technology examined extremely ancient rocks from Greenland.Evidence of the existence of terrestrial magnetism on Earth about 3.7 billion years agoI found it. This is the oldest evidence of terrestrial magnetism. In addition, since its strength is not so weak compared to today, it is an important discovery for studying the composition of the Earth's magnetic field and how ancient life evolved and increased in number.

■Geomagnetism is important for life and the atmosphere

As indicated by the fact that the compass points north, the Earth has a unique magnetic field.Terrestrial magnetism“Exists. The Earth's magnetic field is much stronger than the magnetic field of other celestial bodies, and is characterized by being the strongest among celestial bodies that are composed of solid materials such as rocks.

It is believed that the presence of terrestrial magnetism is one of the reasons why the Earth became a celestial body that harbors life. The Earth's magnetic field has many benefits, but the most important is thisGuards against high-energy charged particles (electrified particles) such as solar wind that rain down from spaceThere is something called. This is an important benefit for life on Earth. These charged particles are harmful to living organisms and can damage cells, DNA, etc. If there was no Earth's magnetic field, living organisms would not be able to escape the ocean.

Another important benefit is the role it plays in preventing atmospheric loss. As mentioned earlier, without the Earth's magnetic field, charged particles such as those generated by the solar wind would collide directly with the atmosphere. When high-energy particles collide, they can transfer enough kinetic energy to the molecules that make up the atmosphere to overcome gravity. In other words, the weaker the Earth's magnetic field, the easier it is for molecules to escape, and the thinner the atmosphere becomes. In fact, Mars, which has very similar characteristics to Earth's, has a very thin atmosphere, and one reason for this is thought to be due to its magnetic field Weak, which could not prevent the atmosphere from flowing out(※1).

*1…Another factor is that gravity is less than half that of Earth, which means the force holding atmospheric molecules in place is weak.

This indicates that the Earth's strong magnetic field acts as a powerful shield that protects life and the atmosphere. The timing of the Earth's magnetic field is an important element in understanding the evolution of life and the Earth itself, but it is extremely difficult to know.

To know the strength of Earth's magnetism in past eras, it is necessary to examine ancient magnetism, which is the remaining magnetic field in rocks that hardened from magma during that era. However, the magnetic field etched into rock is information that is extremely easy to disappear. When a rock is heated to several hundred degrees Celsius, its magnetic field is “erased” and then “overwritten” with information from the Earth's magnetic field when it cools again.

For this reason, even if we examine the paleomagnetic properties of very old rocks, the paleomagnetic information obtained does not necessarily match the age at which the rocks cooled and solidified. To show that solidified rocks have never been “erased” and “overwritten” by a magnetic field, we need to show that they have never been exposed to high temperatures in the past. However, in addition to the technical difficulties involved, it is difficult to find rocks that have not been heated at least once over billions of years, so there was very little evidence to know about the Earth's magnetic field.

■It is difficult to obtain evidence of terrestrial magnetism since ancient times.

Nicholls and his team focused on rocks collected in the Esua region in southwest Greenland, which is known for producing particularly ancient rocks, to find traces of the Earth's magnetic field shortly after its birth, and checked to see if there were any traces left. The Esua region is known as An area that produces some of the world's oldest rocks dating from between 3.7 and 3.8 billion years ago, there are claims that the world's oldest traces of life have been found there.(※2).

*2…There is a claim that sedimentary rocks containing stromatolite (a layered structure produced by photosynthetic bacteria) were collected, but there is debate as to whether the layered structure is stromatolite.

Nicholls and his colleagues focused on the Isua region for reasons other than the fact that the rocks formed very old. Beneath the Isua region there is very thick continental crust. This stable continental crust is characterized by very little tectonic movement or volcanic activity. The lack of geological activity means that large-scale activity becomes less frequent. If the activity is intense enough to penetrate the Earth's crust, which is thicker than other places, it will occur less frequently. This means that the rocks in the Isua region may have existed without ever being exposed to high temperatures for a very long history of 3.7 billion years.

However, this alone was not sufficient evidence, so Nicholls and others developed another method to prove that the rock had not been exposed to heat: radiometric dating, by which the age could be determined by measuring the radioactive elements present in the rock and also verified using the “measurement method”. There are many radiometric dating methods that use different elements, and it is known that some of these methods can “reset” when exposed to heat. When dating is performed using multiple radioactive elements, all ages should match if there is no reset, but if a specific date is reset, there will be a discrepancy between the measured ages. Nicholls and his colleagues focused on proving that there was no discrepancy in the ages measured by various radiometric dating methods, and that this was not due to other causes, such as chemical changes that did not involve heat.

■We have found evidence of the existence of terrestrial magnetism 3.7 billion years ago!

The results showed that the rock samples examined had never been exposed to temperatures exceeding 380 degrees Celsius in the 3.7 billion years since their formation. In other words,Paleomagnetism carved into rocks reflects Earth's magnetism 3.7 billion years agoit will be. This is the oldest evidence of terrestrial magnetism.

The measured geomagnetic field was at least 15 microtesla. This is more than half of the current 30 microtesla geomagnetic field, but due to the nature of the measurement,Earth's magnetism 3.7 billion years ago was about the same level as it is today.It shows that.

This fact was surprising. In the case of the current terrestrial magnetism generation model, it is believed that terrestrial magnetism did not exist immediately after the Earth's formation, but was enhanced as the Earth's internal structure formed. The fact that the Earth's magnetic field 3.7 billion years ago was as strong as Earth's current force means that an internal structure similar to today's would have formed in about 800 million years. This provides important clues in studying the formation and evolution of the Earth.

The fact that the Earth's magnetic field 3.7 billion years ago was as strong as it is today is noteworthy from another perspective. The Earth today is full of oxygen, but oxygen did not appear in the atmosphere until about 2 billion years ago, and before that, although oxygen was produced through photosynthesis, the other situation was that it reacted with materials and was quickly consumed.

It is believed that one of the conditions for oxygen to exist without being consumed is the reduction of hydrogen-containing substances from the atmosphere.(※3). For the hydrogen to escape, it would be appropriate for the solar wind to collide with the atmosphere frequently, but for that to happen, Earth's magnetic field would have to be weaker than its current level. It has been found that the strength of the Earth's magnetic field has changed many times in the past, but the results of this research indicate that there was a period of time when the strength of the Earth's magnetic field temporarily weakened for more than a billion years. . She suggests. However, it cannot currently be determined whether this estimate is correct or not, due to the lack of paleomagnetic records from ancient times. Further investigation and research will be needed to reach a conclusion.

*3…The decrease in xenon in the atmosphere supports the assumption that hydrogen has decreased due to atmospheric outflow caused by solar wind, etc. Since xenon is an inert gas that undergoes almost no chemical reactions and is a heavy atom, an external factor such as the solar wind must exist to expel it in large quantities from the atmosphere.

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Text / Riri Ayaka Editing / sorae editorial department