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For hundreds of years, Are we alone in the universe? has been the ultimate question for science.
数百年来，我们都是宇宙里唯一的生物吗？这已经成为科学的终极问题了。
And while astronomers are busy searching for life beyond Earth, they've also started asking another question:
虽然天文学家忙着搜寻地球外的生命，他们也开始思考另一个问题：
If life seems so difficult to find, then why is our world so full of it?
如果生命看起来很难寻找的话，为何地球上到处生机盎然呢？
One answer might be overhead right now: the Moon.
有一个答案可能是呼之欲出的：月球。
Moons are all over the solar system—bigger ones and smaller ones—but there's something unique about ours.
太阳系里到处都是卫星——有大一点儿的，有小一点儿的——但地球的卫星却与众不同。
All of Jupiter's moons combined are just two hundredths of a percent as massive as Jupiter.
木星的所有卫星加起来，质量不过是木星1%的2/200。
A similar ratio holds for Saturn and Neptune's moons, while the Uranian and Martian moons are even less massive compared to their planets.
土星和海王星卫星所占的质量比也与此类似，而天王星和火星的卫星与其行星相比质量就更小了。
In comparison, our single moon is a whopping 1.2% of the Earth's mass—which means its effects aren't exactly subtle.
对比之下，地球唯一的卫星月球居然占地球质量的1.2%——这意味着其对地球的影响就不能说很微小了。
In particular, the Moon's gravity causes tides that affect huge swathes of the planet.
尤其有一点是：月球的引力会引发潮汐，影响地球的很多地方。
And while it's hard to know anything for sure when you're talking about billions of years in the past, there are good reasons to suspect that those tides played a large role in shaping life as we know it.
虽然现在谈论的是几十亿年前的事儿，有些地方很难确定。但我们还是有充足的理由怀疑潮汐对于生命的形成有着巨大作用的。
For one, tides likely played a key role in creating the basic conditions for life.
一方面，潮汐很有可能在创造生命基础条件上发挥着重要作用。
That's because tides don't just affect water.
这是因为潮汐不仅会影响水。
Even though we think of tides as rising and falling ocean levels, tides actually affect the entire surface of the Earth.
虽然我们把潮汐视为上涨下落的海平面，但潮汐其实会影响整个地球的表面。
For example, New York City can rise and fall more than 35 centimeters in a day.
比如，纽约市一天的潮汐涨落有35厘米以上。
But while water can simply flow to its new shape every time the tides go up and down, the Earth's crust is full of rock that twists and grinds on itself, creating friction that releases heat.
不过，虽然每次潮汐涨落的时候，水都可以通过流动而形成新的形状，但地壳里满是岩石，岩石不断变形重组，形成了摩擦并产生了热量。
Earth already gets a lot of heat from radioactive decay in the mantle, and all of this heat helps move around the pieces of the crust we know as tectonic plates.
地从已经通过地幔发生的放射性衰变而获得了很多热量，这些热量有助于地壳构造板块的移动。
As these plates move around, creating earthquakes, volcanos, and new mountains, they also release elements critical to life, like phosphorus, copper, and zinc, that come from the Earth's mantle.
这些板块会来回移动，形成地震、火山爆发、新的山体，也会形成生命必需的元素，如磷、铜、锌，这些都来自地幔。
And as old land gets pulled back into the mantle, it traps the greenhouse gas carbon dioxide underground, which helps keep the planet cool.
久远的土地被拉回到地幔中，地下存储着温室气体二氧化碳，有助于保持地球的凉爽。
What's left is a delicate balance of temperature and nutrients that sets the stage for life to arise.
剩下的是温度与营养物的微妙平衡，这个平衡为生命的出现打下了基础。
And the tides may have had a role in that next step as well.
这些潮汐可能对下一步也起到了作用。
We don't know for sure how life got its start, but one of the most famous models describing the origin of life is the primordial soup theory.
我们不知道生命是如何开始的，但描述生命起源最著名的一个模型是原始汤理论。
In this scenario, Earth's early oceans were full of the basic building blocks of life, like amino acids.
在该理论的设定下，地球早期的海洋里满是构成生命的基础组成元素，比如氨基酸。
Under just the right circumstances, a very lucky combination of these ingredients could have created the first life.
在正确的条件下，将这些原材料以幸运的方式进行组合可能就产生了地球上的第一批生命。
In particular, that cocktail would have had to include one important ingredient—a way of copying itself, or making more life from life.
尤其是，这一大锅炖必须要包含一个重要的元素——一种自我复制的方式，或者说，从生命中制造更多生命的方式。
Today's replicating molecules are DNA and RNA, and the backbone of these structures is made of phosphate.
今天可复制的分子是DNA和RNA，它们的聚合分子主链是由磷酸盐组成的。
To make copies of genetic information, they have to come together and separate—a process that's sometimes described as zipping and unzipping.
要复制基因信息，就要聚合和分离——也就是分子链形成和分离的过程。
Early life likely had replicating molecules that worked similarly and were also made of phosphate.
早期的生命可能有复制的分子，其机理与此相似。而且也是由磷组成的。
The catch is, in normal, low-salt ocean water, phosphates repel each other and block one strand of phosphates from connecting to another.
问题在于：正常情况下的低盐海水。磷彼此排斥，组织磷酸盐链彼此连接。
But in water with higher concentrations of salt, that effect is neutralized.
但在盐浓度稍高的水中，这个效果就有所中和了。
Strands of phosphates can suddenly come together and replicate.
磷酸盐链可能会突然聚集在一起并进行复制。
And the ebb and flow of the tides could have helped make that possible.
潮涨潮落有助于这一过程的发生。
As the tides wash out, seawater gets trapped in tidepools where it can start to evaporate, leaving behind its salt and creating an extra salty environment where the miracle of molecule replication can occur.
潮水冲刷的时候，海水会困在蓄潮池中，海水会开始蒸发，留下盐分并创造出高盐环境，在这种情况下会发生分子复制的奇迹。
Once life got started — however it did — tides continued to shape its development.
一旦生命开始——那么不管以怎样的方式开始——潮汐都会持续改变其发展形成的状态。
Researchers debate whether tides would have helped stabilize or destabilize the Earth's climate over time, but the one thing they agree on is that tides definitely would have influenced it.
研究人员辩论过一个话题——随着时间的流逝，潮汐是否有助于破坏或加强地球气候的稳定。但他们都认同的一点是——潮汐一定会起到影响作用。
See, while tides might seem like a simple in-out motion from any one point on the shore, their movement around the globe is actually pretty complex.
虽然潮汐对岸上的生物来说可能是进进出出的运动而已，但潮汐在全球范围内的移动实际上是相当复杂的行为。
Tidal motion helps set up enormous ocean currents that can redistribute the equator's warm water across the planet and have profound effects on the climate.
潮汐运动有助于形成巨大的洋流，可以在全球范围内重新分配赤道的温暖水体，对气候有着重大影响。
It's hard to predict exactly what happened in the past because the motion of tides and currents depends a lot on the location of the continents and the shape of the ocean floor,
很难判断之前发生过什么，因为潮汐和洋流的运动在很大程度上取决于各个大陆的位置以及海底的形状。
Like, just the appearance of a strip of land connecting North and South America—the Isthmus of Panama—a few million years ago
比如，几百万年前，连接南北美洲的一块狭长土地出现了——巴拿马地峡。
was enough to cut off circulation between the Atlantic and Pacific Oceans and completely change the shape of ocean currents.
几百万年前的出现足以切断大西洋和太平洋之间的循环，也足以彻底改变洋流的形状。
Because of that change, a new, Gulf Stream current started carrying warm water up north, making Northern Europe as much as 10 degrees Celsius warmer than it used to be.
由于这一变化的发声，一条新的墨西哥湾流开始带着温暖的水体向北流动，让北欧的水域比之前提高了10摄氏度。
And there's no doubt that shifts in the climate, affected by the tides, drove much of life's evolution.
毫无疑问，受到潮汐影响的气候变化会驱使生命进化。
Even today, tidal motion is increasing the melting of ice in the Arctic by carrying warmer water up and under the sheets of sea ice.
即便是今天，潮汐运动也在加剧北极区的冰川融化，方式就是带着温暖的水体向北流动，在海洋冰川下流动。
Of course, Earth isn't the only place that experiences tides, and tides have actually become a signpost in the search for life.
当然了，地球并非唯一一个有潮汐存在的地方，潮汐其实已经成为寻找生命是否存在的一个路标了。
Tidal heating has created an ocean twice the size of Earth's under the surface of Jupiter's moon Europa.
潮汐热在木卫二的地表下形成了一个海洋，面积是地球海洋的2倍。
And tides from Saturn inject enough heat into its moon Enceladus to create giant geysers that shoot hundreds of kilometers into space.
土星的潮汐释放热量到了土卫二上，因而形成了巨大的间歇泉，向太空中喷射了数百公里。
Places like these—rather than dry, dusty Mars—might be our best hope for life in the solar system.
这样的地方，不同于火星上尘土飞扬的干燥环境，所以它们成为了我们在太阳系中寻找生命的最佳希望。
After all, if the tides helped get life started once, maybe it could happen again.
毕竟，如果潮汐曾助力生命形成过，那么或许这样的事还会再次发生呢？
Thanks for watching this episode of SciShow Space!
感谢收看本期的《太空科学秀》！
And thanks to this month's President of Space, SR Foxley, for helping us bring you this episode!
感谢本月的太空小领队福克西里助力本期节目的制作！
SR is one of our patrons on Patreon, and if you want to find out more about how to join the amazing community of supporters who help make SciShow happen, you can find out more at patreon.com/SciShow.
福克西里是我们的一个忠实粉丝。如果大家想了解更多内容或者想知道如何加入社区帮助节目制作的话，可戳patreon.com/SciShow。
