陨石撞地球，让地球上的生命成为可能

研究发现，陨石撞地球，让地球上的生命成为可能

There’s been more discussion recently about protecting life on Earth from a devastating asteroid strike. But a new study suggests that space rocks actually made life possible on the Blue Planet.

最近有更多关于保护地球生命免受毁灭性小行星撞击的讨论。但一项新的研究表明，太空岩石实际上使蓝色星球上的生命成为可能。

Researchers identified isotopes of selenium in rocks in Earth’s mantle and found identical isotope signatures inside certain meteorites, notably those from the outer solar system.

研究人员鉴定了地球地幔岩石中硒的同位素，并在某些陨石中发现了相同的同位素特征，尤其是那些来自太阳系外的陨石。

“We show that selenium isotopes record a signature of late accretion after core formation and that this signature overlaps only with that of the CI-type carbonaceous chondrites,” the study’s abstract states. “We conclude that these isotopic constraints indicate the late veneer originated from the outer Solar System and was of lower mass than previously estimated. Thus, we suggest a late and highly concentrated delivery of volatiles enabled Earth to become habitable.”

“我们的研究表明，硒同位素记录了岩心形成后的晚期吸积特征，而这种特征只与ci型碳质球粒陨石的特征重叠，”该研究的摘要称。“我们得出的结论是，这些同位素限制表明，晚旋切层起源于太阳系外，其质量低于此前的估计。因此，我们认为挥发性物质的晚期和高度集中的释放使地球变得宜居。”

The selenium isotopes were detected using a method that took samples from mantle rocks, previously brought to the surface from plate tectonic processes and measured.

硒同位素的检测方法是从地幔岩石中提取样本，然后从板块构造过程中带到地表进行测量。

All of this means that selenium, as well as water and other building blocks for life, originated outside of Earth and came to the planet via comets or meteorites, a concept known as panspermia.

所有这些都意味着硒，以及水和其他构成生命的元素，起源于地球之外，并通过彗星或陨石来到地球，这一概念被称为生源说。

“According to our calculations, around 60 percent of the water on Earth today comes from this source. That is the only way oceans could eventually form,” said the study’s lead author, María Isabel Varas-Reus, PhD, in a statement. “This created the conditions for life on Earth to develop in its present form.”

“根据我们的计算，今天地球上大约60%的水来自这个来源。这是海洋最终形成的唯一途径。“这为地球上的生命以现在的形式发展创造了条件。”

Panspermia is the hypothesis that life on Earth originated from microorganisms in outer space that were carried here unintentionally by objects such as space dust, meteoroids and asteroids, according to an article on NASA’s website.

根据美国宇航局网站上的一篇文章，“生源说”是一种假说，认为地球上的生命起源于外层空间的微生物，这些微生物是由太空尘埃、流星体和小行星等物体无意中带到地球上的。

Technically speaking, there should be no selenium seen in the Earth’s mantle, since it is attracted to iron, Varas-Reus explained. As a result, it largely resides in the Earth’s core, which is “iron-rich,” Varas-Reus continued.

从技术上讲，地球的地幔中不应该存在硒，因为它被铁所吸引，因此，在地球的核心是“丰富的铁”，瓦拉斯鲁斯解释道。

However, the selenium that was found in the mantle must have come after the Earth’s core formed, a time period she estimates happened after the moon was also formed, between 4.5 billion and 3.9 billion years ago.

然而，在地幔中发现的硒一定是在地核形成之后，她估计这段时间发生在月球形成之后，即45亿到39亿年前。

It has long been suspected that meteorites brought elements from space and added them to Earth’s mantle, but Varas-Reus said researchers “thought they were meteorites from the inner solar system.”

长期以来，人们一直怀疑陨石将太空中的元素带到地球的地幔中，但瓦拉斯-鲁斯说，研究人员“认为它们是来自太阳系内部的陨石。”

“So we were very surprised that the selenium isotope signature of the Earth’s mantle closely matched a certain type of meteorite from the outer solar system,” Varas-Reus added. “These are carbonaceous chondrites from the solar system beyond the asteroid belt, from the area of the planets Jupiter, Saturn, Uranus and Neptune.”

“因此，我们非常惊讶地发现，地球地幔的硒同位素特征与来自太阳系外的某种陨石非常相似，”瓦拉斯-鲁斯道。“这些碳质球粒陨石来自小行星带之外的太阳系，来自木星、土星、天王星和海王星的区域。”

The study was published in the journal Nature Geoscience.

这项研究发表在《自然地球科学》杂志上。