Earth is naked without its protective barrier. The planet\u2019s magnetic shield surrounds Earth and shelters it from the natural onslaught of cosmic rays. But sometimes, the shield weakens and wavers, allowing cosmic rays to strike the atmosphere, creating a shower of particles that scientists think could wreak havoc on the biosphere. <\/p>\n
This has happened many times in our planet\u2019s history, including 41,000 years ago in an event called the Laschamps excursion. <\/p>\n
<\/p>\n Cosmic rays are high-energy particles, usually protons or atomic nuclei, that travel through space at relativistic speeds. Normally, they\u2019re deflected into space and away from Earth by the planet\u2019s magnetic shield. But the shield is a natural phenomenon and its strength fluctuates, as does its orientation. When that happens, cosmic rays strike the Earth\u2019s atmosphere. <\/p>\n That creates a shower of secondary particles called cosmogenic radionuclides. These isotopes become embedded in sediments and ice cores and even in the structure of living things like trees. There are different types of these isotopes, including ones like Calcium 41 and Carbon 14. <\/p>\n Some of the isotopes are stable, and some are radioactive. The radioactive ones have half-lives ranging from only 20 minutes (Carbon 11) up to 15.7 million years (Xenon 129.) <\/p>\n When Earth\u2019s shield weakens, more of these isotopes reach the planet\u2019s surface and collect in sediments and ice. By studying these cores and sediments, scientists can determine the magnetic shield\u2019s history. Their observations show that Earth experienced a geomagnetic excursion or reversal 41,000 years ago. It\u2019s called the Laschamps excursion after the Laschamps lava flows in France, where geomagnetic anomalies revealed its occurrence. <\/p>\n Every few hundred thousand years, the Earth\u2019s magnetic poles flip. North becomes South and vice versa. In between those major events are more minor events called excursions. During excursions, the poles shift around for a while without swapping places. The excursions weaken the Earth\u2019s shield and can last from a few thousand to tens of thousands of years. When that happens, more cosmic rays strike the atmosphere, creating more radionuclides that shower down onto Earth. <\/p>\n Scientists often focus on one particular radioactive isotope in paleomagnetic studies. Beryllium 10 has a relatively long half-life of 1.36 million years and tends to accumulate on the soil surface. <\/p>\n Sanja Panovska is a researcher at GFZ Potsdam, Germany, who studies geomagnetism. At the recent European Geosciences Union (EGU) General Assembly 2024, Panovska presented new research on the Laschamps excursion. She found that during the Laschamps excursion, production of Be 10 was twice as high as normal. <\/p>\n To understand the Laschamps excursion more thoroughly, Panovska combined cosmogenic radionuclide and paleomagnetic data to reconstruct the Earth\u2019s magnetic field at the time. She found that when the field decreased in strength, it also shrank. The transition from normal field to reversed field took about 250 years, and it stayed flipped for about 440 years. During the transition, the Earth\u2019s shield weekend to as little as 5% of its normal strength. When it was fully reversed, it was at about 25% of its regular strength. This weakening allowed more Be 10 and other cosmogenic radionuclides to reach Earth\u2019s surface. <\/p>\n These radionuclides do more than collect in sediments and ice. Some of them are radioactive. The weakening of the shield also weakened the ozone layer, letting more UV radiation reach Earth\u2019s surface. The high-altitude atmosphere also cooled, which changed the wind flows. This could\u2019ve caused drastic changes on the Earth\u2019s surface. <\/p>\n For these reasons, the Laschamps event has been linked to the extinction of the Neanderthals, the extinction of Australian megafauna, and even to the appearance of cave art. Those links haven\u2019t withstood scientific scrutiny, but that doesn\u2019t mean that events like the Laschamps event aren\u2019t hazardous. If it occurred now, it would knock out our power grids. The Earth\u2019s equatorial region would light up with aurorae. <\/p>\n \u201cUnderstanding these extreme events is important for their occurrence in the future, space climate predictions, and assessing the effects on the environment and on the Earth system,\u201d Panovska said.<\/p>\n Scientists are learning that the magnetic shield isn\u2019t static. There are anomalies. One of them is the South Atlantic Anomaly, a region where the magnetic field is weakest near Earth. When satellites pass over this region, they\u2019re exposed to higher levels of ionizing radiation. The anomaly is likely caused by a reservoir of dense rock inside Earth, illustrating how complex the magnetic shield is. <\/p>\n Scientists are uncertain about what effect the cosmic rays have on life when the magnetic shield is weak. It\u2019s tempting to correlate extinctions with events like the Laschamps excursion when they line up temporally. But the poles have shifted, weakened, and reversed many times and life is still here and still thriving. <\/p>\n If humanity lasts long enough, we\u2019ll go through one of these reversals. Then we\u2019ll know. <\/p>\n![\"Each](\"https:\/\/www.universetoday.com\/wp-content\/uploads\/2024\/05\/Panovska-summary-map.jpg\")
![\"\"](\"https:\/\/www.universetoday.com\/wp-content\/uploads\/2024\/05\/SAA_2020.jpg\")
Like this:<\/h3>\n