Science: Steps Toward Life

Four billion years ago, when the young earth was still enveloped in a deadly atmosphere of ammonia and methane, the first forerunners of life emerged. How those complex molecules were formed remains a profound mystery. But scientists believe that some of the earth's primordial atmospheric molecules were broken up into their constituent atoms; regrouping into new molecules, these atoms formed organic compounds called amino acids, which are the building blocks of protein—and of life.

Exactly what caused that chemical concatenation has long been the subject of lively scientific debate. Was the crucial reaction powered by intense ultraviolet radiation from the sun? By...

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