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1 .This is Scientific American's 60-Second Space. I'm Lee Billings. Got a minute?
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2 .Oxygen and water are crucial to most life on Earth, but what about nitrogen?
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3 .It's in every molecule of DNA in your body, and in all your proteins,you literally can't live without it.
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4 .But most of Earth's nitrogen exists as an inert atmospheric gas that organisms can't use.
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5 .Lightning strikes can convert some nitrogen into a bioavailable form.
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6 .But most of the biosphere's usable nitrogen is the result of bacteria employing an enzyme called nitrogenase to pull nitrogen out of the air.
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7 .Based on genetic evidence, scientists have thought that nitrogenase first evolved around 2 billion years ago.
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8 .Before that, life on Earth might have been confined to the oceans and been limited by the crucial substance's inaccessibility.
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9 .But researchers at the University of Washington now have evidence for the existence of nitrogenase in bacteria going back some 3.2 billion years.
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10 .The researchers base their argument on the ratios of light to heavy nitrogen isotopes in ancient rocks from Australia.
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11 .The study is in the journal Nature.
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12 .The finding indicates that the biosphere more than three billion years ago was much more complex than previously appreciated, and perhaps had already colonized land.
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13 .An earlier arrival for nitrogenase also may mean that the enzyme evolves more easily than was previously believed.
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14 .Which could increase the odds that, sooner or later, astrobiologists will find signs of another robust biosphere on some world far away.
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15 .Thanks for the minute, for Scientific American's 60-Second Space. I'm Lee Billings.
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