内容来源：https://www.quantamagazine.org/where-did-earth-get-its-oceans-maybe-it-made-them-itself-20260612/

内容总结：

地球之水何处来？新研究指向“自我制造”

长期以来，科学界普遍认为地球的海洋源自彗星或小行星的撞击。但近年来，这一传统理论正面临挑战。随着探测器对彗星样本的深入分析，科学家发现彗星上的水与地球水的化学“指纹”——氘氢比（D/H比值）并不吻合，部分彗星的重水含量甚至远高于地球。这一发现让“彗星起源说”逐渐失宠。

小行星随后成为主流假说。研究显示，某些小行星（如龙宫小行星）的水分子与地球海洋极为相似。然而，小行星中惰性气体（如氩、氪、氙）的比例又与地球存在差异，且“撞击时间窗口”的科学依据仍存争议。

在此背景下，一种颠覆性的新理论悄然兴起：地球可能自己“制造”了大部分水。科学家推测，早期地球拥有富含氧气的岩浆海洋和富含氢的大气层。在高温高压条件下，氢与岩浆中的氧发生化学反应，就能生成水。实验室模拟显示，当氢气在极高压力下与激光熔化的岩石反应时，产水量惊人，远超预期，最高可达理论预测的1000倍。

不过，这一理论仍存疑点。地球的质量是否足以维持足够高的气压来驱动该反应？科学家意见不一。支持者认为，即使反应时间短暂，也可能足以形成海洋。反对者则指出，地球的质量可能“刚刚处于临界点”。

最新的研究表明，真相或许更为复杂。对彗星67P数据的重新分析发现，此前观测到的重水信号可能受到宇宙尘埃污染。而2025年对彗星12P/Pons-Brooks的观测，又检测到了与地球海洋相似的氘氢比。彗星起源说正“卷土重来”。

目前，多数科学家倾向于一种折中观点：地球的海洋可能来自彗星、小行星以及地球自身化学反应的共同贡献。随着地质、大气和生物过程持续改造，我们或许永远无法找到与水化学完全匹配的“外星源头”。正如科学家所言，这个问题越是深入，答案似乎越模糊，但故事的本身却愈发引人入胜。

中文翻译：

地球的海洋从何而来？或许它自己就是源头
引言
此刻，一艘航天器正从地球飞向木卫二——这颗被冰层包裹的木星卫星被认为拥有与地球海洋在某些方面相似的海洋。美国国家航空航天局（NASA）在一块附在航天器上的金属板上刻下了一首诗，这首诗由时任美国桂冠诗人阿达·利蒙创作。诗中写道：
“将我们联结在一起的并非黑暗，
也不是太空冰冷的距离，而是
水的馈赠，每一滴雨，
每一条溪流，每一次脉搏，每一条血管。”
几十年来，NASA对太阳系的探索一直以在木卫二等地方寻找水为主导，因为据我们所知，水是生命存在的必要条件。
那么，科学家们实际上并不清楚水最初是如何抵达地球的——这或许会令人惊讶。
多年来，最主流的理论是，水是通过彗星来到地球的——这些由冻结物质组成的天体围绕太阳运行，常常拖着闪亮的尾巴。这些诞生于太阳系黎明时期的冰冷残骸，极有可能在它们降落到原始地球时带来了水。但近年来，多艘航天器追上彗星进行了探测。它们发现彗星上的水与地球上的水并不匹配；其化学特征存在差异。
此后，“彗星在一定程度上失宠了”，伦敦自然历史博物馆的陨石学家阿什利·金说道。比彗星更富含岩石和金属的小行星，随后成为最受青睐的对象。小行星撞击地球的频率远高于彗星，而且它们的水储量（尽管不如彗星丰富）与地球上的水更为相似。
但小行星也有自己的问题，于是一个关于行星水来源的激进新观点逐渐兴起。通过仔细观测环绕其他恒星运行的行星，并结合包括金刚石压砧和激光在内的一些爆炸性实验室实验，科学家们意识到，像地球这样的岩质行星有能力自行制造水。你所需要的只是岩浆海洋、大量的氢，以及一点点地质炼金术。
彗星与小行星的对决
地球大约形成于45.4亿年前。由于地质活动中的熊熊烈火与硫磺，其最初亿万年的历史大多已湮没无闻，但基本共识是：它最初是一个主要由熔岩构成的球体，后来才变成了蓝色弹珠。这究竟是如何发生的？
彗星提供了一个颇具说服力的答案。它们通常远离地球，滞留在海王星之外一个名为“柯伊伯带”的环状冰冷天体高速公路上，或是更遥远、更朦胧的奥尔特云中。但当彗星足够靠近太阳时，其冰和冻结气体转化为蒸汽，形成可绵延数亿公里的彗尾（据已知案例，最长的超过十亿公里）。与小行星相比，彗星能带来“更高的性价比”，牛津大学的陨石学家詹姆斯·布赖森说道。
科学家们曾认为彗星可能撞击地球并为其提供了水。但直到20世纪80年代，欧洲空间局（ESA）决定进行验证，才无人能证明彗星含有与地球类似的水。他们的首次深空探测任务“乔托号”雄心勃勃：它将是首个近距离详细观测彗星冰核的航天器。
1986年，它追上了哈雷彗星——这颗彗星因大约每76年与地球轨道相交一次而闻名于世。“乔托号”成功传回了彗核的震撼图像以及对其周围物质云团的测量数据。让科学界为之侧目的是“乔托号”测得的所谓“氘氢比”。
地球上几乎所有的水都由两个氢原子和一个氧原子构成：H₂O。但还有一种水，称为重水，由一个氧原子和两个较重的氢同位素（氘）原子组成。
如果彗星是地球海洋的来源，那么人们会期望“乔托号”发现哈雷彗星上的水与地球上的水具有相似的氘氢比。但结果并非如此。“根本不匹配，”夏威夷大学行星天文学家凯伦·米奇说道。事实上，哈雷彗星的氘氢比是地球上大多数水的两倍。
在20世纪90年代和21世纪初，对海尔-波普彗星等其他彗星的光谱观测也发现了重水的证据，这给彗星理论带来了更多破绽。但决定性一击出现在2014年，当时NASA的“罗塞塔号”任务作为“乔托号”的精神继承者，通过环绕一颗形似巨型橡皮鸭的彗星——67P/丘留莫夫-格拉西缅科彗星——并将着陆器送至其表面，创造了历史。在环绕67P彗星期间，“罗塞塔号”进行了迄今最精确的彗星成分测量——并发现它含有我们测量过的所有彗星中最高的氘浓度。
如果地球的水并非来自彗星，那么或许来自小行星。这些岩石天体大多位于火星和木星之间，并经常以陨石的形式撞击我们的星球，尽管它们的大部分物质在大气层中燃烧殆尽或落入海洋。科学家们已收集了数万块陨石，并发现其中特定一组所含的水分子与地球上的极为相似。2021年，一颗坠入英国宁静小镇温奇科姆的陨石——在一家车道上留下了一个相当大的凹痕——被发现其氘氢比几乎与地球海洋的完美匹配。
然而，陨石在炽热的下坠和撞击着陆过程中可能受到污染。这就是为什么科学家们会发射航天器前往小行星，并在轨道上收集物质进行法医学分析。在一些案例中，他们发现仍在太空运行的小行星似乎也含有与地球相似的水。2023年发表的一项研究表明，日本航天局于2018年造访过的小行星“龙宫”上的水，其氘氢比与地球上大多数水相似。谈及地球水的来源，“目前科学界可能更偏向小行星而非彗星，”金说道。
但小行星的氘氢比并未为地球水的来源问题画上句号。小行星也含有微量的惰性气体，如氩、氪、氙——这些惰性元素可作为各种地质过程的示踪剂——科学家们发现这些混合物的成分通常与地球上的不符。此外，基于彗星和小行星的理论都有一个根本问题：这两类天体为地球提供海洋的能力都依赖于偶然性。多个小行星或彗星必须在其超高温岩浆海洋阶段之后撞击地球，才能形成我们今天所居住的这个被水淹没的世界。这在过去被视为理所当然，但科学界对于这种晚期轰击是否真实存在存在激烈争议。
还有另一种可能性，它不依赖于宇宙的偶然性，而是依赖于地球自身的“勤勉”：地球自行制造了它的大部分水。
氢，遇见岩浆
当天文学家观察系外行星——我们太阳系之外的世界——时，他们看到了多样的大气层。但科学家们模拟行星形成方式后发现，其中许多行星可能最初都充满了氢。地球的形成时期是否也是如此？
科学家们过去认为早期地球几乎没有氢。他们在分析一种名为“顽火辉石球粒陨石”的陨石后得出了这一结论，这种陨石的化学成分与地球惊人地相似。布赖森说，由于这种相似性，科学家们认为两者可能由相同的物质形成。这些陨石似乎缺乏氢，因此科学家们认为地球也是如此。
但包括布赖森参与合著的一项研究在内的一些研究发现，这些陨石中一直存在着氢。它只是隐藏在它们的有机分子、硅酸盐玻璃和硫化合物中。那么，地球在早期也可能充满了氢。
地球的岩浆海洋富含氧。在2023年发表的一篇论文中，三位科学家推测，如果行星大气层中的氢与岩浆中的氧以某种方式混合，会发生什么。氢不会自发地与氧结合，因此它们并非最情愿的化学伙伴。尽管如此，研究人员得出结论，这样的过程可以让行星自行制造水；他们只是不确定能制造多少。
两年后，由劳伦斯利弗莫尔国家实验室的物理学家哈里森·霍恩、亚利桑那州立大学的地球物理学家沈师航以及其他研究人员进行的一系列雄心勃勃的实验，为他们的理论提供了生机。
除其他目标外，他们想了解为什么次海王星——这些常见的系外行星直径是地球的两到四倍——能够拥有富含水的大气层（正如望远镜观测所暗示的那样），即使它们距离其炽热的主恒星非常近。氢大气层与岩浆海洋之间的反应是否足以解释这个现象？
他们怀疑这有可能，但前提是大量的氢对岩浆施加了足够的压力。“更高的压力是促进水生成的一个关键因素，”霍恩说，“它实际上增强了化学反应。”
为了测试他们的模型，研究团队希望再现存在于年轻次海王星上的极端（且极其危险的）条件。他们需要使用称为“金刚石压砧”的特殊工具，将高度易燃的氢气置于强压之下，然后将其与用激光熔化的岩石样本结合。他们花了五年时间才开发出安全有效进行这些实验所需的技术。“我们弄坏了很多金刚石，”沈师航说，“这是一段激动人心的旅程。”
他们曾希望氢和氧能反应生成水。结果确实如此，而且反应程度极为剧烈：高压氢与激光熔化岩石的反应效率如此之高，以至于产生的水量比科学家预测的多达1000倍。（另一项大约同时发表的实验室研究报告了类似的结果。）“快速产生巨量水并非不合理，”圣路易斯华盛顿大学的行星科学家保罗·伯恩说。而且“这完全是自产自销的原生水”——无需彗星或小行星。
这是否意味着地球创造了自己的海洋？这一点上情况变得有些模糊。“该论文并未对地球做出强有力的断言，”霍恩说。但他和沈师航都认为这是一个有效的关联。“这是可能发生的，”沈师航说。
其他科学家同意，地球上一部分水可能自行形成——但可能远不足以产生其海洋。“我认为，早期通过与氢反应产生一些水当然是可能的，”加州大学圣克鲁兹分校的实验地球物理学家昆廷·威廉姆斯说，“但能产生多少则相当难以捉摸。”
问题在于，没有人知道地球早期大气层中是否有足够的氢来产生反应所需的压力。次海王星的质量远大于地球，其强大的引力更善于留住氢。“地球恰好处于这类反应可能开始发生的边缘，”霍恩说。
一些科学家不认为地球有足够的能力大规模制造自己的水。“我有点怀疑对于地球质量大小的行星能否发生这种情况，”丹麦哥本哈根大学和瑞典隆德大学的天体物理学家安德斯·约翰森说。但伯恩表示，次海王星实验表明，该反应不需要持续很长时间就能产生巨量水。地球可能只在某一瞬间是“水工厂”，但那一瞬间或许足以形成海洋。
如果真是这样，那么其影响远远超出了我们自己的太阳系。也许无数行星都满足这一可能成为生命存在必要条件的状况，因为正如伯恩所说，它们“生来就富含水”。
淹没在可能性之海
地球的水至少有一部分可能来自行星自身的过程。但这并非故事的结局：彗星正在卷土重来。
当“罗塞塔号”在2014年遇到鸭形彗星67P时，科学家们已经研究了其他11颗彗星的水。除了一个例外，所有这些彗星的氘氢比都与地球的不同。2011年，欧洲空间局的赫歇尔空间天文台发现，哈特利2号彗星上的水具有更接近地球的特征。
这一观测结果似乎是个异常值。但在2024年发表的一篇论文中，科学家们重新审视了“罗塞塔号”对67P彗星的分析——并发现太空可能篡改了数据。在样本采集时，“罗塞塔号”正飞过含有重水的尘埃。彗星冰体本身被这些尘埃包围，可能实际上相当类似地球。随后，在2025年发表的一篇论文中，对12P/庞斯-布鲁克彗星的观测检测到了与地球海洋非常相似的氘氢比。
那么，到底是彗星一直以来的功劳？还是小行星？抑或是地球独立开启了水龙头？“我怀疑是所有这些因素的结合，”米奇说。也许很难为地球的水化学找到完美匹配的地外来源，因为它是一种如此多样化的混合物——而且随着时间的推移，还经过了地球的地质、大气和生物过程的调整与过滤。“我们可能永远无法知晓，”米奇说。
但这并不意味着科学家们会停止尝试回答关于地球以及最终关于我们自身存在的最基本问题之一。“这就像在问，生命的起源是什么？”米奇说，“你知道得越多，就越发现所知甚少——但故事却变得更加丰富、更加激动人心。”

英文来源：

Where Did Earth Get Its Oceans? Maybe It Made Them Itself.
Introduction
At this moment, a spacecraft is headed from Earth to Europa, an ice-veiled moon of Jupiter thought to contain an ocean similar in some ways to one of our own. NASA engraved a metal plate affixed to the spacecraft with a poem, commissioned from Ada Limón during her time as poet laureate of the United States. It reads, in part:
And it is not darkness that unites us,
not the cold distance of space, but
the offering of water, each drop of rain,
each rivulet, each pulse, each vein.
For decades, NASA’s exploration of the solar system has been dominated by the search for water in places like Europa, because as far as we know, water is essential for life.
It may come as a surprise, then, that scientists don’t really know how water first arrived here on Earth.
For years, the top theory was that water came to our planet via comets — objects made of frozen matter that orbit the sun, often decorated with sparkling tails. In all likelihood, these icy relics, which came into being at the dawn of the solar system, did bring water with them when they rained down on a primeval Earth. But in recent years, several spacecraft caught up to comets to examine them. What they found was that cometary water didn’t match ours; the chemical signatures were different.
After that, “comets sort of fell out of favor,” said Ashley King, a meteoriticist at the Natural History Museum in London. Asteroids — rockier and more metal-rich than comets — then became the most popular choice. Asteroids impact Earth far more frequently than comets do, and their water reserves (while not as voluminous as those of comets) look a lot more like those on our planet.
But asteroids have their own problems, and a radical new idea about planetary water is gaining steam. Through careful observation of worlds orbiting other stars, along with some explosive laboratory experiments involving diamond anvils and lasers, scientists have realized that rocky planets like Earth have a way to make water all by themselves. All you need is an ocean of magma, a whole lot of hydrogen, and a little bit of geological alchemy.
A Showdown Between Comets and Asteroids
Earth formed about 4.54 billion years ago. Through geologic fire and brimstone, much about its earliest eon has been lost to history, but the basics are agreed upon: It began as a ball of mostly molten rock. Then it became a blue marble. How?
Comets provided a well-motivated answer. They often linger far from Earth in a doughnut-shaped highway of icy objects beyond Neptune called the Kuiper Belt, or in the even more distant and nebulous Oort cloud. But when a comet passes close enough to the sun, its ice and frozen gases turn to vapor, creating a tail that can stretch for hundreds of millions of kilometers (in one known case, more than a billion). Compared to asteroids, comets give you “a lot of bang for your buck,” said James Bryson, a meteoriticist at the University of Oxford.
Scientists thought comets could have crashed to the Earth and provided its water. But nobody could prove that comets contained Earth-like water — until the 1980s, when the European Space Agency (ESA) decided to check. Giotto, their first deep-space mission, was truly ambitious: It would be the first spacecraft to get an up-close-and-personal look at a comet’s icy heart.
In 1986, it caught up to Halley’s comet, famous for appearing in Earth’s sky as our paths intersect roughly every 76 years. Giotto managed to send home both dramatic images of the comet’s nucleus and measurements of the cloud of material around it. What raised scientific eyebrows was Giotto’s measurement of something called the D/H ratio.
Almost all the water on Earth is made up of two hydrogen atoms and one oxygen atom: H2O. But there is another form of water, called heavy water, made up of one oxygen atom and two atoms of a heavier form of hydrogen called deuterium.
If comets are responsible for our oceans, one might expect Giotto to have found that the water on Halley’s comet had a similar ratio of deuterium to hydrogen as the water on Earth. That’s not what it found. “It didn’t match at all,” said Karen Meech, a planetary astronomer at the University of Hawai‘i. In fact, Halley’s D/H ratio was twice that of most of the water on Earth.
More cracks appeared in the comet theory during the 1990s and 2000s, when spectroscopic observations of other comets, like Hale-Bopp, also found evidence of heavy water. But the hammer blow arrived in 2014 when the spiritual successor to Giotto, ESA’s Rosetta mission, made history by orbiting and sending a lander to the surface of 67P/Churyumov-Gerasimenko, a comet shaped like a giant rubber duck. During its orbits of 67P, Rosetta made the most precise measurements of a comet’s composition to date — and found that it contained the highest concentration of deuterium of any comet we’ve measured.
If Earth’s water didn’t come from comets, perhaps it came from asteroids. These rocky objects mostly hang out between Mars and Jupiter, and they impact our planet all the time as meteorites, though most of their material burns up in the atmosphere or lands in the ocean. Scientists have collected tens of thousands of meteorites and found that the water molecules contained in a particular group closely resemble those in our world. One meteor that plunged into the sleepy British town of Winchcombe in 2021 — leaving a sizable dent in a family’s driveway — was found to have a D/H ratio that almost perfectly matched that of Earth’s oceans.
Meteorites, though, can be contaminated during their fiery dives and crash landings. That’s why scientists have flown spacecraft out to asteroids and collected material in orbit for forensic analysis. In some cases, they have found that asteroids still moving through space also seem to have Earth-like water. A study published in 2023 revealed that water from the asteroid Ryugu, which Japan’s space agency visited in 2018, had a D/H ratio similar to that of most water on Earth. When it comes to the provenance of Earth’s water, “the community is probably more favorable of asteroids than comets these days,” King said.
But the D/H ratios of asteroids did not close the book on the question of Earth’s water. Asteroids also contain small amounts of noble gases like argon, krypton, and xenon — inert elements that act as tracers of various geologic processes — and scientists have found that those mixtures do not usually correspond to what we find on our planet. In addition, theories based on comets and asteroids have the same fundamental problem: The ability of either type of object to give the planet its oceans relies on luck. Multiple asteroids or comets would have had to impact Earth after its superhot magma ocean phase to produce the inundated world we live on today. This was taken for granted in the past, but the existence of this late-in-the-day bombardment is heavily debated in the scientific community.
There is another possibility, one that relies not on cosmic chance, but on our planet’s own industriousness: Earth made most of its water by itself.
Hydrogen, Meet Magma
When astronomers look at exoplanets — worlds outside our solar system — they see a diversity of atmospheres. But when they simulate the ways the planets took shape, scientists find that many of them could have started out brimming with hydrogen. Could Earth’s formative years have been similar?
Scientists used to think that the early Earth had little hydrogen. They reached this conclusion after examining meteorites called enstatite chondrites that have a suspiciously similar chemical makeup to Earth. Because of this similarity, scientists think the two probably formed from the same material, Bryson said. These meteorites seemed to lack hydrogen, so scientists thought the same went for our planet.
But some studies, including one co-authored by Bryson, found that there was hydrogen in the meteorites all along. It was just hidden in their organic molecules, silicate glasses, and sulfur compounds. Perhaps, then, Earth was also awash in hydrogen in its early days.
Earth’s ocean of magma was full of oxygen. In a paper published in 2023, three scientists wondered what might happen if the hydrogen in a planet’s atmosphere and the oxygen in its magma were to mix — somehow. Hydrogen doesn’t just spontaneously bind to oxygen, so they aren’t the most willing chemical partners. Still, the researchers concluded that such a process would let a planet make its own water; they just weren’t sure how much.
Two years later, they were thrown a lifeline by an ambitious set of experiments built by the researchers Harrison Horn, a physicist at Lawrence Livermore National Laboratory; S.-H. Dan Shim, a geophysicist at Arizona State University; and others.
Among other things, they wanted to know how sub-Neptunes, commonplace exoplanets two to four times the diameter of Earth, can have atmospheres rich in water, as telescopic observations suggest, even when they hew close to their scorching-hot host stars. Could a reaction between a hydrogen atmosphere and a magma ocean be enough?
They suspected it could, but only if a huge amount of hydrogen put the magma under a sufficient amount of pressure. “That higher pressure is a big part of what facilitates the water production,” Horn said. “It actually enhances the chemical reactions.”
To test their model, the team wanted to re-create the extreme (and extremely dangerous) conditions present on adolescent sub-Neptunes. They needed to put hydrogen, a highly flammable gas, under intense pressure using special tools called diamond anvils, and then combine it with rock samples melted with lasers. It took them five years to develop the techniques they needed to conduct these experiments safely and effectively. “We broke a lot of diamonds,” Shim said. “It was an exciting journey.”
They had hoped the hydrogen and oxygen would react to make water. And that’s what happened, to the extreme: The reaction of high-pressure hydrogen and laser-melted rock was so efficient that it made up to 1,000 times more water than scientists predicted. (A second laboratory study, published around the same time, reported similar results.) “It doesn’t seem unreasonable [that you could] produce a huge amount of water quite quickly,” said Paul Byrne, a planetary scientist at Washington University in St. Louis. And “this is all homegrown, indigenous water”— no comets or asteroids required.
Does that mean Earth created its own oceans? This is where the waters get a little murky. “The paper doesn’t make strong claims about Earth,” Horn said. But both he and Shim think it’s a valid link to make. “It could happen,” Shim said.
Other scientists agree that some amount of water could have formed on Earth — but perhaps not nearly enough to produce its oceans. “I’d say it’s certainly possible that some water could be generated by reaction with hydrogen early on,” said Quentin Williams, an experimental geophysicist at the University of California, Santa Cruz. “How much might be generated is, however, pretty enigmatic.”
The issue is that nobody knows if there was enough hydrogen in Earth’s early atmosphere to create the pressure the reaction seems to need. Sub-Neptunes are far more massive than Earth, and their intense gravity is better at holding on to hydrogen. “Earth is right on the edge of where that kind of thing can start happening,” Horn said.
Some scientists don’t think Earth had the heft to manufacture its own water at scale. “I’m a little bit doubtful whether you can have this for an Earth-mass planet,” said Anders Johansen, an astrophysicist at the University of Copenhagen in Denmark and at Lund University in Sweden. But, Byrne said, the sub-Neptune experiments suggest that the reaction wouldn’t need to last long to create an enormous quantity of water. Earth might have been a water factory for only a moment, but that moment may have been enough to forge oceans.
If that’s the case, then the implications stretch far beyond our own solar system. Perhaps countless planets meet what may be a necessary condition for hosting life because, as Byrne said, they “are born water-rich.”
Drowning in a Sea of Possibilities
It’s possible that at least some of Earth’s water came from processes on the planet. But that’s not the end of the story: Comets are making a comeback.
By the time Rosetta met the duck-shaped comet 67P in 2014, scientists had studied the water of 11 other comets. All had D/H ratios unlike Earth’s — except one. In 2011, ESA’s Herschel Space Observatory found that the water in the comet Hartley 2 had a much more Earth-like signature.
The observation seemed anomalous. But in a paper published in 2024, scientists reinvestigated Rosetta’s analysis of comet 67P — and found that space may have tampered with the data. At the time of the sample collection, Rosetta had been flying through dust that contained heavy water. The icy comet body itself, surrounded by this dust, may have been fairly Earth-like after all. Then, in a paper published in 2025, observations of comet 12P/Pons-Brooks detected a D/H ratio much like that of Earth’s oceans.
So, was it comets all along? Or asteroids? Or did Earth turn on the taps independently? “I suspect it was a combination of all of them,” Meech said. Perhaps it’s hard to find a perfect extraterrestrial match for our planet’s watery chemistry because it’s such a diverse cocktail — one that’s also been tweaked and filtered over time by Earth’s geologic, atmospheric, and biologic processes. “We may never know,” Meech said.
But that doesn’t mean scientists will stop trying to answer one of the most fundamental questions about Earth and, ultimately, our own existence. “It’s like asking, what’s the origin of life?” Meech said. “The more you learn, the less you know — but the story becomes richer and more exciting.”