原文取材自： http://www.universetoday.com/2008/01/09/earth-barely-habitable/ Written by Fraser Cain Earth, Barely Habitable? 地球，勉强能住人？ Our home planet has been often described in glowing, nurturing terms. A cradle for life, right in the goldilocks zone. But our planet is actually right on the edge of habitability. If it were any smaller, and a little less massive, plate tectonics might never have gotten started. It turns out, life needs plate tectonics. 我们的地球老家常被形容为一片欣欣向荣，正好处於的生命摇篮。但我们 的行星其实位在适居区的边缘。如果地球的尺寸或质量再小一点，就可能永远不 会产生板块构造运动。而事实是，生物需要板块构造运动。 Astronomers at the Harvard-Smithsonian Center for Astrophysics announced their research today at the Winter meeting of the American Astronomical Society. According to the team, plate tectonics only really get going when a planet gathers enough mass. And the Earth has just barely enough mass to enjoy plate tectonics. 哈佛─史密松尼亚天文物理中心的天文学家，在美国天文学会冬季会议上宣布他们 的发现。据他们的研究，板块构造运动只会在行星拥有足够质量的情况下发生。而 地球勉强达到及格的质量享受板块运动的好处。 "Plate tectonics are essential to life as we know it," said Diana Valencia of Harvard University. "Our calculations show that bigger is better when it comes to the habitability of rocky planets." 「就我们所知，板块构造运动对生命来说很重要，」哈佛大学的戴安娜‧瓦伦西亚 表示：「我们的计算显示，石质行星越大越适合生物居住。」 When a planet reaches a large enough size, huge chunks of the planet's surface can float atop an ocean of boiling magma. These plates spread apart and crash into one another, lifting up gigantic mountain ranges like the Himalayas. 当一颗行星达到足够大的质量，行星表面的巨大岩块能浮在岩浆海上方。这些板块 四散且互相撞击，抬昇起巨大的山脊，例如喜玛拉雅山脉。 And without plate tectonics, we wouldn't be here. The process enables complex chemistry and recycles carbon dioxide, which acts like a blanket to keep the Earth warm and hospitable for life. Carbon dioxide is locked into rocks, and then returned to the atmosphere when the rocks melt. Without this cycle, carbon dioxide would get locked away in rocks forever. 没有板块构造运动，我们根本不会出现。板块构造运动使复杂的化学作用成行，并能 让二氧化碳循环，其作用有如一条能让地球保温以适居的毛毯。二氧化碳被锁入岩石 中，并藉由岩石熔化而释放回大气里。没有这循环，二氧化碳会永远被封存入岩石。 The researchers examined what would happen on different rocky planets. They looked at a range of planets, smaller than our planet, up to the so-called "super-Earths" - planets twice our size with 10 times the mass. Any bigger than that, and you start to get a gas planet. 研究者检验在不同的石质行星上会发生什麽事。他们调查的范围包括比地球小的 行星，以及比地球大十倍的所谓「超级地球」。超过这个尺寸，那将会是气态而非 石质行星了。 According to their calculations, the Earth is barely habitable. If you get a planet with more mass, the plate tectonics really get rolling, and the carbon cycle becomes really active. A super-Earth could have globe-spanning rings of fire, bursting with hot springs and geysers. Life would have every opportunity to get started. 根据计算，地球刚好勉强适合居住。如果你有颗更大质量的行星，板块构造运动将非 常兴盛，而碳循环也会非常活跃。超级地球将有广布於全球的火山带，喷发温泉及间 歇泉，有充份的机会发展出生命。 Of course, if we tried to visit a super-Earth, we'd find the gravity uncomfortable. We'd experience 3 times the gravity trying to walk around on the surface of the planet. Oh, my back. 当然，若我们造访超级地球，那边的重力可不会好受。我们在行星表面行走时会体验 到三倍於地球的重力。噢，我的背。 But for native life forms, it would be paradise. 但对当地居民来说，那可是天堂呢。 --

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