首先，他们必须搞清楚火星上是否曾经存在过生命。
To begin with, they will have to find out whether life has ever existed on the planet of Mars in the past.
由于自然选择，大多数曾经存在过的物种已经灭绝，所以这不是一个新现象。
Thanks to natural selection, most species that have ever lived has already gone extinct, so this is not a new phenomenon.
木星、土星、天王星和海王星。这些都是气体行星，是太阳系的四个重量级。但曾经存在第五个行星吗？
Jupiter, Saturn, Uranus, and Neptune. Those are the gas giants, the four heavyweights of the solar system. But was there once a fifth?
工作中曾经存在大量问题。
由于大多数行星科学家认为水是生命的基本要素，因此黄钾铁矾的存在意味着火星上曾经存在出现生命的先决条件之一。
Since most planetary scientists believe that water is essential to life, the presence of jarosite means that one prerequisite for life was once present on Mars.
不幸的是，从考古学证据的性质来看，这类人物总是难以捉摸的，因为考古学证据几乎是一成不变的，只是曾经存在过的东西的一种样品。
Unfortunately, it is in the nature of the archaeological evidence, which is almost invariable only a sample of what once existed, that such figures will always be elusive.
解释：火星上曾经存在生命么？
这更容易让人相信它们曾经存在过。
事实上，我不知道他们是否曾经存在。
据说她看起来非常像曾经存在过的雷龙。
She is reputed to look very much reminiscent of the Brontosaurus.
曾经存在的一丝不信任变得越来越强烈：我讨厌国家。
What was once merely a vague sense of distrust has given way to a much stronger feeling: I hate the state.
惧怕是你对一条曾经存在的危险的蛇的惧怕。
Fear is when you react to a dangerous snake as if it were, well, dangerous.
你不要想以掩饰曾经存在的证据来掩饰思维。
Don't think you are going to conceal thoughts by concealing evidence that they ever existed.
这些生物也许是之前曾经存在过的生物的一部分。
These creatures would be the remnants of the previous inhabitants.
曾经存在的必须释放，以拥抱正在创造的新世界。
What "has been" must be released in order to embrace the new world in the making!
只要痛楚提醒着我他曾经存在过，你们都曾经存在过。
The pain is my only reminder that he was real, that you all were.
大多数古代的泥炭森林都逐渐消失，只留下曾经存在过的零星证据。
Most ancient peat forests die gradually, leaving only spotty evidence of what grew there.
对于每个曾经存在的不公正，总是有一群人为结束这种不公正而奋争。
For every injustice that has ever existed, there has always been a group of people fighting to end that injustice.
这一发现不仅显示了地球上可能存在其他类型的生命，或者曾经存在过。
The finding not only presents the possibility that alternative life forms can exist, or once existed, on Earth.
这只巨塔般的掠食者，以及象目的恐象，是地球上曾经存在的最大的哺乳动物。
This towering plant eater, along with Deinotherium — a member of the order elephants belong to — were the largest mammals to ever walk the earth.
所有那些曾经存在的，以及你将描述的，不是很快走入未来就是倒退消失。
All that there ever was still exists and you can as you would describe it, go back in time or into the future.
在数十亿曾经存在过的人中，没有一个人的心跳是和你完全一样的，这是不可思议的。
It's amazing that out of all the billions of people who've ever lived, no one has ever had a heartbeat exactly like yours.
在我死后一年，谁会还记得我面孔，记得这个世界上还曾经存在过这么一个人。
After my death one year, who will remember my face, remember that this world has ever existed, so a person.
由于曾经存在对于这条河水质的投诉，居民一定是因为他们认为河水不够干净才不在这里活动。
Since there have been complaints about the quality of the water in the river, residents must be avoiding the river because they think that it is not clean enough.
木星，土星，天王星和海王星。这些都是气体行星，太阳系的四个重量级。但曾经存在第五个行星吗？
Jupiter, Saturn, Uranus and Neptune. Those are the gas giants, the four heavyweights of the solar system. But was there once a fifth?
铁幕在当时并没有完全被打破，但是那个晚上，任何小步走的可能性就不复存在了，即使曾经存在过。
The Iron Curtain did not unravel at that moment, but that night the possibility of cautious, incremental change ceased to exist, if it had ever really existed at all.
铁幕在当时并没有完全被打破，但是那个晚上，任何小步走的可能性就不复存在了，即使曾经存在过。
The Iron Curtain did not unravel at that moment, but that night the possibility of cautious, incremental change ceased to exist, if it had ever really existed at all.
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