原文取材自： http://www.universetoday.com/2008/01/09/earth-barely-habitable/ Written by Fraser Cain Earth, Barely Habitable? 地球，勉強能住人？ 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. 我們的地球老家常被形容為一片欣欣向榮，正好處於的生命搖籃。但我們 的行星其實位在適居區的邊緣。如果地球的尺寸或質量再小一點，就可能永遠不 會產生板塊構造運動。而事實是，生物需要板塊構造運動。 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─史密松尼亞天文物理中心的天文學家，在美國天文學會冬季會議上宣佈他們 的發現。據他們的研究，板塊構造運動只會在行星擁有足夠質量的情況下發生。而 地球勉強達到及格的質量享受板塊運動的好處。 "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." 「就我們所知，板塊構造運動對生命來說很重要，」哈佛大學的戴安娜‧瓦倫西亞 表示：「我們的計算顯示，石質行星越大越適合生物居住。」 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. 當一顆行星達到足夠大的質量，行星表面的巨大岩塊能浮在岩漿海上方。這些板塊 四散且互相撞擊，抬昇起巨大的山脊，例如喜瑪拉雅山脈。 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. 沒有板塊構造運動，我們根本不會出現。板塊構造運動使複雜的化學作用成行，並能 讓二氧化碳循環，其作用有如一條能讓地球保溫以適居的毛毯。二氧化碳被鎖入岩石 中，並藉由岩石熔化而釋放回大氣裡。沒有這循環，二氧化碳會永遠被封存入岩石。 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. 研究者檢驗在不同的石質行星上會發生什麼事。他們調查的範圍包括比地球小的 行星，以及比地球大十倍的所謂「超級地球」。超過這個尺寸，那將會是氣態而非 石質行星了。 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. 根據計算，地球剛好勉強適合居住。如果你有顆更大質量的行星，板塊構造運動將非 常興盛，而碳循環也會非常活躍。超級地球將有廣佈於全球的火山帶，噴發溫泉及間 歇泉，有充份的機會發展出生命。 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. 當然，若我們造訪超級地球，那邊的重力可不會好受。我們在行星表面行走時會體驗 到三倍於地球的重力。噢，我的背。 But for native life forms, it would be paradise. 但對當地居民來說，那可是天堂呢。 --

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