The Origin of Life

According to modern science’s version of Genesis -- less colorful than the biblical story, but no less wonderful -- Earth was born, together with the Sun and the other planets, in a whirlwind of gas and dust, some 4.5 billion years ago, a little more than nine billion years after the Big Bang. A half-billion years later, our planet had recovered sufficiently from the pangs of its violent birth to become physically capable of harboring life. After less than another half-billion years, it did indeed harbor life, in particular an entity, called the last universal common ancestor (LUCA), that gave rise through evolution to all known living creatures, including microbes of various kinds, plants, fungi, animals, and humans.

Primitive organisms arose from nonliving matter in what were probably hot, sulfurous, metal-laden, volcanic waters. This unsavory brew was likely “spiced” with abundant small organic molecules such as amino acids, sugars, nitrogenous bases, and other typical components of biological constituents. One of the most astonishing discoveries of the last decades, revealed by exploration of space, nearby celestial objects, and especially meteorites that fell to Earth, is that many of the chemical building blocks of life form spontaneously throughout the universe. Organic chemistry, so named because it was believed to be a prerogative of living organisms, has turned out to be the most widespread and banal chemistry: the chemistry of carbon.

How this “cosmic chemistry” gave rise to the first living cells is not known in detail, but the process may be summed up in two words. The first is chemistry , the essence of life. Living beings continually manufacture their own constituents from small inorganic and organic building blocks, with the help of catalysts called enzymes and of energy derived from sunlight, mineral sources, or foodstuffs made by other organisms. Something similar happened in the origin of life, but along pathways, by the action of catalysts, and with sources of energy that remain to be identified.

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