The "invisible shield" that secretly protects the Earth

Produced by: Science Popularization China

Author: Digital World

Producer: China Science Expo

The Earth's magnetic field is an environmental factor that is indispensable to human life. It plays a significant role in the evolution of the Earth, biological activities and human life. The Earth's magnetic field is also generally referred to as the geomagnetic field. Geomagnetism generally refers only to the measurement and research of the geomagnetic field, but geomagnetism includes geomagnetism, rock magnetism, paleomagnetism and the origin and evolution of the Earth's magnetic field.

1. Changes and applications of the Earth's magnetic field

Long-term and worldwide observations and studies of the Earth's magnetic field have shown that the Earth's magnetic field changes over time and space. Therefore, many places have established geomagnetic observatories or stations to continuously observe and record changes in the Earth's magnetic field. my country has established geomagnetic observatories (stations) in Beijing, major administrative regions, and some important provinces and cities.

Earth's magnetic field (Image source: veer Gallery)

These changes in the geomagnetic field not only provide a lot of information about the structure and activity of the earth, but also have many important applications. For example, magnetic prospecting has become an important and commonly used method in geophysical prospecting. It has its own characteristics with other geophysical prospecting methods such as gravity method and electrical method. Magnetic prospecting can be applied not only to the exploration of iron ore, but also to the exploration of other minerals associated with iron ore. The former is called direct magnetic prospecting, such as the exploration of magnetite, hematite, vanadium-titanium magnetite and gold-copper magnetite, and the latter is called indirect magnetic prospecting, such as the survey and exploration of metal deposits containing nickel, chromium, cobalt, etc., non-metallic deposits such as diamond, boron, asbestos, and petroleum mines.

There are many applications for the observation and study of the Earth's magnetic field and related geomagnetic phenomena. In addition to magnetic prospecting, there are also magnetic orientation and magnetic navigation for compasses; sudden changes in the Earth's magnetic field (magnetic storms) can be used to predict solar activity and space weather; geomagnetic disturbances and magnetic storms can affect radio communications and climate; abnormal changes in the Earth's magnetic field are related to earthquakes and volcanic activities, and therefore may be used as a factor in predicting earthquakes and volcanoes; and observations of the Earth's magnetic field combined with other geophysical observations can be used for geological surveys.

2. Reversal of the Earth's Magnetic Field

Modern scientific research shows that the Earth's magnetic field was formed and evolved as the Earth was formed and evolved. However, how do we know how the Earth's magnetic field changes during the Earth's evolution? What information about the Earth's evolution can be obtained from these changes?

The changes in the Earth's magnetic field over billions of years of the Earth's evolution are obtained from observational studies of the magnetism of continental and oceanic rocks in various geological periods.

After long-term observation and research on the magnetism of strongly magnetic rocks in different geological periods on various continents and oceans on the earth, that is, the observation and research on the residual magnetism of the magnetism when the rocks were formed and retained until the present observation, it is mainly shown that the direction of the residual magnetism of these ancient rocks, that is, the direction of the earth's magnetic field when the rocks were magnetized by the earth's magnetic field when they were formed, some are the same as the current direction of the earth's magnetic field (called positive), and some are opposite to the current direction of the earth's magnetic field (called reverse).

During the long-term evolution of the earth, the magnetic direction (polarity) of ancient rocks formed in different geological periods has changed due to the change in the direction of the earth's magnetic field. In addition, the age of ancient humans and ancient cultural relics can be determined based on the residual magnetism of ancient rocks and the residual magnetism of ancient ceramics and other cultural relics, which is called archaeomagnetism. my country has used paleomagnetic dating methods to determine the age of Peking Man, Yuanmou Ape Man in Yunnan, and Wushan Man in Sichuan. The results are consistent with the ages determined by other scientific archaeological dating methods.

3. Aurora, a gift from the Earth’s magnetic field

The Earth's aurora is a beautiful luminous phenomenon that occurs in the Earth's North Pole and South Pole regions and the surrounding high altitudes. It is brightly colored and has a variety of shapes. Humans have observed and recorded this luminous phenomenon thousands of years ago, and it is called the Northern Lights. However, for a long time, no one knew the cause of the aurora, let alone the relationship between the aurora and the Earth's magnetic field. It was not until the development of modern science that it was figured out that the time of occurrence, form of expression, and changes of the aurora are closely related to the Earth's magnetic field.

Northern Lights (Photo source: veer photo gallery)

The formation of the aurora is mainly due to the fact that charged particles from the sun are emitted into the sphere of influence of the earth's magnetic field. Under the influence of the earth's magnetic field, they enter the earth's high-altitude atmosphere from high latitudes and stimulate high-level air particles to cause luminescence. The earth is a huge magnet, and its magnetic poles are near the north and south poles. We know that the compass always points to the north and south directions because it is affected by the geomagnetic field. The charged particle flow from the sun is also affected by the geomagnetic field, and the charged particle flow gathers near the magnetic poles. Therefore, most auroras appear in the sky near the north and south poles. The one that occurs in the South Pole is called the Southern Lights, and the one that occurs in the North Pole is called the Northern Lights.

Now, issues such as the mechanism and reversal of the Earth's magnetic field have become cutting-edge topics in the field of geophysical research. I believe that scientists will lead us to further uncover the mystery of this invisible shield.