Dinosaur-killing impact crater might have been teeming with life
Dinosaur-killing impact crater might have been teeming with life
导致恐龙灭绝的撞击坑可能曾是生命的温床
About 66 million years ago, the Chicxulub asteroid smashed into Earth, kicking up tsunamis and dropping hot debris that annihilated non-avian dinosaurs and many other species. But not everything it left in its wake was destructive. This space rock hit what is now the partially submerged Yucatan Peninsula, and at the bottom of the ocean, the impact generated enough heat to create a hydrothermal system that persisted for 8 million years and may have been a hotbed of life.
大约 6600 万年前，希克苏鲁伯（Chicxulub）小行星撞击了地球，引发了海啸并抛洒出炽热的碎片，导致非鸟类恐龙及许多其他物种灭绝。但它留下的并非全是毁灭。这颗太空岩石撞击了如今部分被淹没的尤卡坦半岛，在海底，撞击产生的热量足以形成一个持续了 800 万年的热液系统，这可能曾是生命的温床。
When researchers drilled for samples in the impact zone in 2016, they studied the types of rock that had formed as a result of the asteroid strike. This gave more insight into what happened in the immediate and long-term aftermath of this cataclysmic event. The collision was intense enough to cause deformation far beneath the surface. Subterranean effects reached 35 km (almost 22 miles) down, and included the melting an immense amount of rock. Exposure to seawater made that rock porous. As hot water seeped into the pores, a hydrothermal system formed. The hot water gushing into an isolated region of the freezing depths could have attracted microorganisms and possibly other life forms that were otherwise struggling to survive.
2016 年，研究人员在撞击区钻取样本时，对因小行星撞击而形成的岩石类型进行了研究。这使人们更深入地了解了这一灾难性事件发生后，短期和长期内所发生的情况。这次碰撞的强度足以导致地表深处发生变形。地下影响深达 35 公里（近 22 英里），包括大量岩石的熔化。暴露在海水中使这些岩石变得多孔。随着热水渗入孔隙，一个热液系统便形成了。热水涌入冰冷深海的孤立区域，可能会吸引微生物以及其他在当时难以生存的生命形式。
More recently, another team of researchers, led by geologist and planetary scientist Annemarie Pickersgill of the SUERC Center for Isotope Sciences at the University of Glasgow, studied the rock samples for more evidence of its formation and longevity. What they found was that both the scale of this hydrothermal system and how long it lasted had previously been underestimated. It was thought to have been around for only 2 million years, but the new analysis found evidence that it remained in the depths under the Yucatán Peninsula at least four times longer than that.
最近，由格拉斯哥大学 SUERC 同位素科学中心的地质学家兼行星科学家安娜玛丽·皮克斯吉尔（Annemarie Pickersgill）领导的另一研究团队，对这些岩石样本进行了研究，以寻找其形成和持续时间的更多证据。他们发现，该热液系统的规模及其持续时间此前都被低估了。人们原以为它只存在了 200 万年，但新的分析发现，它在尤卡坦半岛下方的深处存在的时间至少是之前的四倍。
“Longer periods of hydrothermal activity will generate extended windows of opportunity for prebiotic chemical reactions to occur, life to develop, and micro-organisms to thrive and propagate beyond their point of origin,” Pickersgill said in a study published in Communications Earth & Environment.
“更长的热液活动周期将为前生物化学反应的发生、生命的演化以及微生物在起源地之外的繁衍提供更广阔的机会窗口，”皮克斯吉尔在发表于《通讯-地球与环境》（Communications Earth & Environment）的一项研究中表示。
Fathoms below and eons ago
深海之下，亿万年前
Hydrothermal systems created by other impacts are all over the planet. Although these systems are considered habitable because of heat and nutrients, signs of life have been hard to find, and linking the timing of an impact to processes that contributed to the flourishing of life is even harder. Microbes have only been found to colonize eight of the 70 underwater impact craters with hydrothermal activity. What Pickersgill and her team wanted to find out was whether the Chicxulub impact could have created habitable conditions, so she analyzed rock samples to figure out when there was the highest chance of habitability.
由其他撞击产生的热液系统遍布全球。尽管这些系统因具备热量和营养物质而被认为是宜居的，但生命迹象却很难找到，将撞击时间与促进生命繁荣的过程联系起来则更为困难。在 70 个具有热液活动的水下撞击坑中，仅有 8 个被发现有微生物定居。皮克斯吉尔和她的团队想要探究的是，希克苏鲁伯撞击是否创造了宜居条件，因此她分析了岩石样本，以确定何时存在最高的宜居可能性。
The work doesn’t answer whether the hydrothermal system in that crater was actually inhabited. The researchers delved into how long the impact crater brought about temperatures and additional conditions that would have been ideal for attracting and holding on to life. Habitable conditions that endure for long periods allow more time to attract organisms that build colonies around a hydrothermal vent. To determine the duration of the Chicxulub hydrothermal system, Pickersgill recovered samples at the site, drilling 1 km down. She then took radioisotopic measurements of feldspar samples recovered from the site. Feldspar contains potassium, and the decay of that potassium into argon can give an idea as to how old the rock is. Lunar rocks and volcanic formations have been dated this way.
这项工作并未回答该撞击坑中的热液系统是否真的存在生命。研究人员深入探讨了该撞击坑维持理想温度及其他吸引并留住生命条件的时间长度。长期持续的宜居条件能提供更多时间来吸引生物在热液喷口周围建立群落。为了确定希克苏鲁伯热液系统的持续时间，皮克斯吉尔在现场钻探了 1 公里深并回收了样本。随后，她对回收的长石样本进行了放射性同位素测量。长石含有钾，钾衰变为氩的过程可以推断岩石的年龄。月球岩石和火山地层就是通过这种方式测定年代的。
Life finds a way … and a heat source
生命总会找到出路……以及热源
Traces of argon found inside a rock are indicative of potassium decay. Since the gas will also escape from molten rock, this provides a measure of when the rock solidified. How much time has passed since that rock melted can be determined from potassium-argon dating, which involves measuring the amount potassium-40 isotope present relative to the argon-40 it decays into. Levels of argon meant the hydrothermal system stayed heated from 66 million years ago, when the asteroid first hit, to 58 million years ago. With 8 million years of heat and nutrients, life had more than enough time to colonize the hydrothermal system in the Chixculub crater.
岩石内发现的氩痕迹是钾衰变的标志。由于气体也会从熔融岩石中逸出，这提供了一种衡量岩石何时固化的方法。通过钾-氩测年法可以确定岩石熔化后过去了多少时间，该方法涉及测量存在的钾-40 同位素相对于其衰变产物氩-40 的含量。氩的含量表明，该热液系统从 6600 万年前小行星撞击时起，一直保持加热状态直到 5800 万年前。拥有 800 万年的热量和营养物质，生命有足够的时间在希克苏鲁伯撞击坑的热液系统中定居。
Pickersgill also ran computer simulations of hydrothermal activity in that location. Results suggested that cooling to 90° C (194° F) took between 1.5 and 2.3 million years after the impact at depths of one kilometer. Cooling to below 50° C (122° F) took up to 5 million years, still enough heat for colonies of microbes to thrive. After 6 million years, significantly less hot water was flowing, and by 8 million years, the flow had ceased. These results matched the rock age found by isotope analysis.
皮克斯吉尔还对该地点的热液活动进行了计算机模拟。结果显示，在 1 公里深处，撞击后冷却至 90°C (194°F) 需要 150 万到 230 万年。冷却至 50°C (122°F) 以下则需要长达 500 万年，这对于微生物群落的繁衍来说热量依然充足。600 万年后，热水的流动显著减少，到 800 万年时，流动完全停止。这些结果与同位素分析得出的岩石年龄相吻合。
Finding how long hydrothermal systems lasted on Earth can guide habitable environments elsewhere. “Chicxulub is still relatively small compared to the impact basins expected on early Earth and observed on other planetary bodies,” said Pickersgill. “It is therefore possible that these larger impacts could have created even longer-lived hydrothermal systems and, hence, could have been able to maintain the temperatures and fluid flux required for habitable environments for a minimum of several million years.”
探究地球上热液系统的持续时间可以为寻找其他地方的宜居环境提供指导。“与早期地球上预期的以及在其他行星体上观测到的撞击盆地相比，希克苏鲁伯仍然相对较小，”皮克斯吉尔说。“因此，这些更大的撞击可能创造了寿命更长的热液系统，从而能够维持宜居环境所需的温度和流体通量至少数百万年。”