STARSET_MirrorWhat killed dinosaurs and other life on Earth?
Determining what killed the dinosaurs 66 million years ago at the end of the Cretaceous Period has long been the topic of debate, as scientists set out to determine what caused the five mass extinction events that reshaped life on planet Earth in a geological instant. Some scientists argue that comets or asteroids that crashed into Earth were the most likely agents of mass destruction, while others argue that large volcanic eruptions were the cause. A new Dartmouth-led study published in the Proceedings of the National Academy of Sciences (PNAS) reports that volcanic activity appears to have been the key driver of mass extinctions.
在6600万年前的白垩纪末期，是什么杀死了恐龙，这一直是一个争论的话题，科学家们开始确定是什么导致了五次大灭绝事件，在地质瞬间重塑了地球上的生命。一些科学家认为，撞击地球的彗星或小行星最有可能是大规模破坏的罪魁祸首，而另一些科学家则认为，大型火山喷发是原因。达特茅斯学院领导的一项新研究发表在《美国国家科学院院刊》(PNAS)上，报告称火山活动似乎是大规模物种灭绝的关键驱动因素。
The findings provide the most compelling quantitative evidence so far that the link between major volcanic eruptions and wholesale species turnover is not simply a matter of chance.
这些发现提供了迄今为止最令人信服的定量证据，表明大型火山爆发和物种大规模更替之间的联系不仅仅是一个偶然的问题。
Four of the five mass extinctions are contemporaneous with a type of volcanic outpouring called a flood basalt, the researchers say. These eruptions flood vast areas — even an entire continent — with lava in the blink of a geological eye, a mere million years. They leave behind giant fingerprints as evidence — extensive regions of step-like, igneous rock (solidified from the erupted lava) that geologists call “large igneous provinces.”
研究人员说，五次大灭绝中有四次与一种被称为洪水玄武岩的火山喷发同时发生。这些火山爆发在地质学上一眨眼的时间，仅仅一百万年的时间里，就使大片地区——甚至整个大陆——充满了熔岩。它们留下了巨大的指纹作为证据——广泛的阶梯状火成岩区域(由喷发的熔岩凝固而成)，地质学家称之为“大火成岩区”。
To count as “large,” a large igneous province must contain at least 100,000 cubic kilometers of magma. For context, the 1980 eruption of Mount St. Helens involved less than one cubic kilometer of magma. The researchers say that most of the volcanoes represented in the study erupted on the order of a million times more lava than that.
要算“大”，一个大火成岩省必须包含至少10万立方公里的岩浆。举例来说，1980年圣海伦斯火山喷发的岩浆不到一立方公里。研究人员表示，研究中所涉及的大多数火山喷发的熔岩量都是这一数字的100万倍。
The team drew on three well-established datasets on geologic time scale, paleobiology, and large igneous provinces to examine the temporal connection between mass extinction and large igneous provinces.
研究小组利用了地质时间尺度、古生物和大火成岩省的三个成熟数据集，来研究大规模灭绝和大火成岩省之间的时间联系。
“The large step-like areas of igneous rock from these big volcanic eruptions seem to line up in time with mass extinctions and other significant climatic and environmental events,”says lead author Theodore Green ’21, who conducted this research as part of the Senior Fellowship program at Dartmouth and is now a graduate student at Princeton.
“这些大火山喷发形成的巨大阶梯状火成岩区域似乎与大灭绝和其他重大气候和环境事件的时间一致，”21岁的首席作者西奥多·格林(Theodore Green)说。他进行了这项研究，作为达特茅斯学院高级奖学金项目的一部分，现在是普林斯顿的研究生。
In fact, a series of eruptions in present-day Siberia triggered the most destructive of the mass extinctions about 252 million years ago, releasing a gigantic pulse of carbon dioxide into the atmosphere and nearly choking off all life. Bearing witness are the Siberian Traps, a large region of volcanic rock roughly the size of Australia.
事实上，大约在2.52亿年前，今天西伯利亚的一系列火山爆发引发了最具破坏性的物种大灭绝，向大气中释放出巨大的二氧化碳脉冲，几乎窒息了所有的生命。见证这一切的是西伯利亚地盾，这是一大片面积与澳大利亚相当的火山岩地区。
Volcanic eruptions also rocked the Indian subcontinent around the time of the great dinosaur die-off, creating what is known today as the Deccan plateau. This, much like the asteroid strike, would have had far-reaching global effects, blanketing the atmosphere in dust and toxic fumes, asphyxiating dinosaurs and other life in addition to altering the climate on long time scales.
在恐龙大灭绝时期，火山爆发也震动了印度次大陆，形成了今天所知的德干高原。这就像小行星撞击地球一样，会产生深远的全球影响，大气中布满灰尘和有毒气体，恐龙和其他生命窒息，此外还会在很长时间内改变气候。
On the other hand, the researchers say, the theories in favor of annihilation by asteroid impact hinge upon the Chicxulub impactor, a space rock that crash-landed into Mexico’s Yucatan Peninsula around the same time that the dinosaurs went extinct.
另一方面，研究人员说，支持小行星撞击导致地球灭绝的理论取决于希克苏鲁伯撞击器，这是一块太空岩石，大约在恐龙灭绝的同一时间坠落在墨西哥尤卡坦半岛。
“All other theories that attempted to explain what killed the dinosaurs, including volcanism, got steamrolled when the Chicxulub impact crater was discovered,” says co-author Brenhin Keller, an assistant professor of earth sciences at Dartmouth. But there’s very little evidence of similar impact events that coincide with the other mass extinctions despite decades of exploration, he points out.
达特茅斯大学地球科学助理教授布伦欣·凯勒说:“当希克苏鲁伯陨石坑被发现时，所有试图解释恐龙灭绝原因的其他理论，包括火山作用，都被推翻了。”但他指出，尽管经过了几十年的探索，很少有证据表明类似的撞击事件与其他大灭绝同时发生。
At Dartmouth, Green set out to find a way to quantify the apparent link between eruptions and extinctions and test whether the coincidence was just chance or whether there was evidence of a causal relationship between the two. Working with Keller and co-author Paul Renne, professor-in-residence of earth and planetary science at University of California, Berkeley and director of the Berkeley Geochronology Center, Green recruited the supercomputers at the Dartmouth Discovery Cluster to crunch the numbers.
在达特茅斯，格林着手寻找一种方法来量化火山爆发和物种灭绝之间的明显联系，并测试这种巧合是否只是偶然，还是有证据表明两者之间存在因果关系。格林与凯勒和合著者、加州大学伯克利分校地球与行星科学客座教授、伯克利地质年代学中心主任保罗·雷恩(Paul Renne)合作，招募了达特茅斯发现集群的超级计算机来处理数据。
The researchers compared the best available estimates of flood basalt eruptions with periods of drastic species kill-off in the geological timescale, including but not limited to the five mass extinctions. To prove that the timing was more than a random chance, they examined whether the eruptions would line up just as well with a randomly generated pattern and repeated the exercise with a 100 million such patterns. They found that the agreement with extinction periods was far greater than random chance.
研究人员将洪水玄武岩喷发的最佳估计与地质时间尺度上物种急剧灭绝的时期进行了比较，包括但不限于五次物种大灭绝。为了证明时间不仅仅是一个随机的偶然，他们检查了火山喷发是否与随机生成的模式一致，并对1亿个这样的模式重复了这个实验。他们发现与灭绝期的一致性远远大于随机概率。
“While it is difficult to determine if a particular volcanic outburst caused one particular mass extinction, our results make it hard to ignore the role of volcanism in extinction,” says Keller. If a causal link were to be found between volcanic flood basalts and mass extinctions, scientists expect that larger eruptions would entail more severe extinctions, but such a correlation has not been observed.
“虽然很难确定是否某个火山爆发导致了一次特定的物种灭绝，但我们的研究结果让人们很难忽视火山活动在物种灭绝中的作用，”凯勒说。如果在火山泛滥玄武岩和物种大灭绝之间找到了因果关系，科学家们预计更大的喷发将导致更严重的物种灭绝，但这种相关性还没有被观察到。
Rather than considering the absolute magnitude of eruptions, the research team ordered the volcanic events by the rate at which they spewed lava. They found that the volcanic events with the highest eruptive rates did indeed cause the most destruction, producing more severe extinctions up to the mass extinctions.
研究小组没有考虑火山爆发的绝对规模，而是根据火山喷发的速度来排序。他们发现，喷发率最高的火山事件确实造成了最大的破坏，产生了更严重的灭绝，直到大规模灭绝。
“Our results indicate that in all likelihood there would have been a mass extinction at the Cretaceous tertiary boundary of some significant magnitude, regardless of whether there was an impact or not, which can be shown more quantitatively now,” says Renne. “The fact that there was an impact undoubtedly made things worse.”
Renne说:“我们的研究结果表明，在白垩纪第三纪边界极有可能发生过一次规模相当大的大规模灭绝，无论是否有撞击，这一点现在可以更定量地显示出来。”“撞击的事实无疑让事情变得更糟。”
The researchers ran the numbers for asteroids too. The coincidence of impacts with periods of species turnover was significantly weaker, and dramatically worsened when the Chicxulub impactor was not considered, suggesting that other smaller known impactors did not cause significant extinctions.
研究人员也对小行星进行了计算。影响与物种更替周期的重合性明显较弱，当希克苏鲁伯撞击物不考虑在内时，情况急剧恶化，这表明其他已知的较小的撞击物没有造成重大灭绝。
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