February 22,2021(Science News)
A magnetic field reversal 42,000 years ago may have contributed to mass extinctions
4万2千年前的磁场逆转可能导致了大灭绝
A flip-flop of Earth’s magnetic poles between 42,000 and 41,000 years ago briefly but dramatically shrank the magnetic field’s strength — and may have triggered a cascade of environmental cris on Earth, a new study suggests.
一项新的研究表明，在42000年到41000年前，地球磁极的一次巨变短暂但戏剧性地缩小了磁场的强度，并可能在地球上引发了一连串的环境危机。
With the help of new, preci carbon dating obtained from ancient tree fossils, the rearchers correlated shifts in climate patterns, large mammal extinctions and even changes in human behavior just before and during the Laschamps excursion, a brief reversal of the magnetic poles that lasted less than a thousand years. It’s the first study to directly link a magnetic pole reversal to large-scale environmental changes, the team report
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s in the Feb. 19 Science.新东方学校一对一外语课事件
在从古树化石中获得的新的、精确的碳定年法的帮助下，研究人员将气候模式的变化、大型哺乳动物的灭绝，甚至人类行为在Laschamps(持续了不到1000年的磁极短暂逆转)之前和期间的变化联系起来。该研究小组在2月19日的《科学》杂志上报道说，这是第一个将磁极逆转与大规模环境变化直接联系起来的研究。
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During a reversal, Earth’s protective magnetic field, which shields the planet from a barrage of charged particles streaming from the sun, can lo strength. So some rearchers have suggested that the flip-flops may be linked to extinction events.
在逆转过程中，地球的保护性磁场（它保护地球免受来自太阳的带电粒子流的密集攻击）会失去强度。因此，一些研究人员认为，这种逆转可能与物种灭绝事件有关。
百灵科But evidence for this has proven elusive. In fact, “the general belief had been that geomagnetic changes had no impact on climate or anything el,” says Alan Cooper, an evolutionary biologist at BlueSky Genetics in Adelaide. One reason for that belief is a dea九月英文缩写
rth of preci dates for the timing and duration of the geomagnetic event to correlate with environmental, ice core and magnetic rock records.
但这方面的证据难以找到。事实上，“人们普遍认为地磁变化对气候或其他任何事情都没有影响，”阿德莱德蓝天基因公司的进化生物学家艾伦·库珀说。这种看法的一个原因是缺乏与环境、冰芯和磁性岩石记录相关联的地磁事件的时间和持续时间的精确日期。
Enter New Zealand’s kauri tree, among the most ancient in the world. The country’s swampy bogs prerve the relics of kauri trees dating as far back as the Laschamps excursion. Cooper and his colleagues obtained cross-ctions from four ancient trees recovered from a swamp at Ngāwhā Springs in northern New Zealand, and analyzed them for carbon-14, a radioactive form of carbon.
claude kelly初一英语知识点新西兰贝壳杉，世界上最古老的树之一。这个国家的沼泽保存着贝壳杉树的遗迹，可以追溯到Laschamps之旅。Cooper和他的同事从新西兰北部Ng -āwhā Springs的沼泽中提取了四棵古树的横截面，并对它们进行了碳-14(一种放射性碳)的分析。
In particular, one massive prerved log dating to about 41,000 years ago offered up a 1,700-year-long carbon-14 record. That record revealed major changes in carbon-14 during the time period running up to and including the excursion, the team reports. That makes n: Increasing incoming cosmic rays — as would occur with a weakened magnetic field — also produce more carbon-14 in the atmosphere, a carbon signature which would then become incorporated into the tree’s tissues.wellpoint
尤其值得注意的是， 这些大约41000年前的古数记录了1700年间的碳-14记录。研究小组报告说，这一记录揭示了碳-14在Laschamps的大迁徙之前以及包括那次迁徙在内的这段时间内的主要变化。这是有道理的:随着磁场减弱，越来越多进入大气层的宇宙射线也会产生更多的碳-14，这是一种碳特征，然后会被吸收到树的组织中。
The team simulated how a weakened magnetic field might alter atmospheric weather patterns. The computer analysis suggested that the increa of charged particles entering the atmosphere would also increa the production of atmospheric hydrogen and nitrogen oxides — molecules that tend to consume ozone. That would reduce the abi
lity of stratospheric ozone to shield Earth’s denizens from ultraviolet radiation. The atmospheric changes would also affect how much sunlight is absorbed at different layers in the atmosphere, leading to large-scale changes in weather patterns that would have cooled the planet.
该小组模拟了减弱的磁场如何改变大气天气模式。计算机分析表明，进入大气的带电粒子的增加也会增加大气中氢和氮氧化物的产生，这些分子往往会消耗臭氧。这将降低平流层臭氧保护地球居民免受紫外线辐射的能力。大气变化也会影响到大气中不同层吸收阳光的量，导致大规模的天气模式变化，从而使地球变冷。
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