Geology Reference
In-Depth Information
Step 1: Bricks and Mortar
No one yet knows exactly how (or when) the ancient transition from a lifeless to a living
world took place, but basic principles are emerging from focused research at dozens of
laboratories around the world. Biogenesis must have occurred as a sequence of steps, each
of which added chemical complexity to the evolving world. First the molecular building
blocks had to come into existence. Then those small molecules had to be selected, con-
centrated, and organized into life's essential structures—membranes, polymers, and other
functional components of a cell. At some point, the collection of molecules had to make
copies of itself, while devising a means to pass genetic information from one generation to
the next. And then evolution by Darwinian natural selection took over; life emerged.
The first and best-understood step in biogenesis was the rampant production of life's
molecular building blocks: sugars, amino acids, lipids, and more. These essential chemic-
als, all based on the versatile element carbon, emerge anywhere that energy interacts with
simple molecules like carbon dioxide and water. Life's raw materials formed where light-
ning pierced the atmosphere, where volcanic heat boiled the deep ocean, even where ultra-
violet radiation bathed molecular clouds in deep space before Earth was born. The seas of
ancient Earth became increasingly concentrated in the stuff of life, as biomolecules rained
from the skies and rose from the depths.
Modern origins-of-life research began in 1953, with what remains to this day the most
famous experiment in biogenesis. Chemist Harold Urey, a Nobel Prize-winning professor
at the University of Chicago, and his resolute graduate student Stanley Miller designed a
simple and elegant tabletop glass apparatus to simulate early Earth. Gently boiling water
proxied for the hot Hadean ocean, and a mixture of simple gases mimicked Earth's prim-
itive atmosphere, while electric sparks simulated lightning. After a few days, the confined,
colorless water turned pinkish, then brown, with a complex mix of organic molecules. The
transparent glass became smeared with sticky black organic sludge.
Miller's routine chemical analyses revealed an abundance of amino acids and other bio-
building blocks. His 1953 paper in
Science,
announcing the results, generated sensational-
isticheadlinesaroundtheworld.Chemistssoonflockedtothestudyofprebioticchemistry.
And while the exact combination of atmospheric gases in the Miller-Urey experiment was
called into question, thousands of subsequent experimental variations on the theme estab-
lished beyond any doubt that early Earth must have abounded in life's essential molecules.
Indeed,the1953sparkexperimentanditsprogenyweresosuccessfulthatmanyinthefield
thought the origins mystery had been largely solved.
This initial enthusiasm and subsequent focus may have come at a price. Miller's master-
fulexperimentplacedorigins-of-liferesearchsquarelyinthecampoforganicchemistsand
established the paradigm of life emerging from a prebiotic soup—perhaps from a “warm
little pond” (echoing Charles Darwin's private speculations from almost a century before).
