The Earth's magnetic field is its protective shell, extending tens of thousands of kilometers into outer space. It affects the Earth's atmosphere, near-Earth objects, and some lunar geological processes. The magnetic field forms a magneto-ground generator – the movement of molten metal in an outer liquid nucleus. Its behavior is quite complex and chaotic, leading to rapid changes in the Earth's magnetic poles. These changes can lead to disastrous processes.
rollback
At the beginning of the 20th century, geophysicists discovered that the magnetic field vector of some rocks is opposite to the direction of the Earth's magnetic field. This is the first evidence of the reversal of the Earth's magnetic field, marking the beginning of a special branch of geology, paleomagnetism. Research in this area has made it possible to determine the age of the Earth's magnetic field – at least 3.5 billion years. It can also be determined that it changes polarity on average every 3 million to 600,000 years, which is quite frequent by Earth standards.
Only an accurate magnetic stratigraphic scale for the last 165 million years of Earth's history is possible. But these are long-term magnetic field reversals. On a geological scale, of course. When the direction of the magnetic pole deviates from the previous position by 45°, there is also a short-term change in the strength of the magnetic field - paleomagnetic shift.
The most studied is the Lachamp-Kargapolovo paleomagnetic shift, where a short-term pole shift of up to a thousand years was observed at the end of the last ice age, 41-42000 years ago. A very popular hypothesis is that it was in connection with this event that the extinction of Neanderthals and cave painting began to flourish.
Ozone depletion
The first evidence of this event was found in the Lachanne lava flow in France in the 60s of the 20th century. During this period, the reverse magnetic field is 75% weaker, while during the transition from the normal magnetic field, it drops from the current value to 5%. Such a strong drop in the strength of the geomagnetic field caused a large number of cosmic rays to begin to reach the Earth's surface. As a result, in the upper layers of the atmosphere, under the influence of the stream of solar particles (solar wind), the cosmogenic isotopes carbon-14 and beryllium-10 began to form.
When a solar neutron collides with a nitrogen atom, the first neutron replaces the proton in its nucleus. Every second, up to 19,000 carbon-14 atoms form on one square meter of the Earth's surface. Beryllium-10 is formed in much the same way. In 2019, a kauri tree was found in a swamp in New Zealand. According to carbon analysis, it proves events that occurred 41-42500 years ago.
Several of his cuts confirmed that the carbon-14 content had changed significantly during this period. A larger solar minima combined with a geomagnetic minima causes more cosmic radiation to reach the Earth's surface, causing the ozone layer to be destroyed in the Earth's atmosphere. This could lead to climate and environmental catastrophes, especially in the equatorial region. Cloudiness increases at low latitudes.
Shelter the caves
Comparisons with other paleoclimatic data collected from lake sediments and ice cores indicate that large ice sheets formed over North America during the La Champe-Calgapolovo event. The tropical rainbands of the western Pacific shifted sharply, followed by the Southern Ocean Wind Belt. Under the influence of intense ultraviolet rays, Australia has turned into a desert. Some representatives of its fauna are extinct. Researchers have built a model that shows how the chemical composition of the Earth's atmosphere changes as the magnetic field weakens.
The results show that even at the equator, the climate has changed significantly, thunderstorms are frequent, and aurora lights are widely distributed. The ionization intensity of the stratosphere was 104-108 times higher than it is now. The lower layers of the atmosphere are 50 times more ionized active. So the aurora can cover the entire planet. Researchers tend to believe that the reason people started using caves as housing is precisely related to these climate changes. They felt the need to find reliable protection in such harsh conditions.
It was in this struggle to find a suitable home that the Neanderthals probably disappeared. Scientists also believe that it was during the trip to La Champu-Calgabolovo that one of the motifs appeared: the handprints used as templates. In order to make their mark on the wall, people dissolved red ochre, held it in their mouths, and sprinkled it on their hands pressed against the stone wall. Ochre may also be used as a sunscreen to prevent the increase in UV radiation.
#挑战30天在头条写日记#