The emergence of life on Earth is on a short list of the biggest unknowns in Science. Did life begin in a small, warm pond at the edge of a primordial sea, as Charles Darwin speculated? Or deep beneath that sea, around one of the burbling hydrothermal vents first seen in the 1970s? and never mind the where: What was it, this initial germ of life? Was it a cell? A replicating molecule?
One of the most intriguing theories says that the answer to the mystery is right inside us. Biologist Harold Morowitz of George Mason University argues that our metabolism – the chemical reactions that allow cells to turn energy and atoms into biologically useful molecules – provides a long fossil record of Earth life. Morowitz and collaborator Eric Smith of the Santa Fe Institute believe that a central set of chemical reactions has been in place since life’s earliest moments about four billion years ago. These reactions involve just 11 small carbon molecules, such as citric and acetic acids - very ordinary stuff that would have been abundant on the young Earth.
Those 11 molecules could have played a role in other chemical reactions that led to the development of such biomolecules as amino acids lipids, sugars, and eventually some kind of genetic molecule such as RNA. In other words, metabolism came first – before cells, before replication, before life as we commonly think of it.
This is probably not what opponents of the teaching of evolution want to hear, but it seems that a kind of molecular natural selection applies event to the world of geochemistry. Some types of molecular chains outcompeted other molecular chains for the plant’s resources, and gradually they led to the kind of molecules that life depends upon – all this before the first living thing oozed forth. Many scientists say life wasn’t a freak accident at all, but the likely outcome of the interaction of the molecules and minerals of the Earth. “Life is an elaboration of something very simple.” Says Smith, “it looks easy and inevitable.’
Earth scientist Robert Hazen’s new book, Ge*ne*sis, says that many theories about the origin of life involve the principle of “emergence.” From simple beginnings, complexity can emerge. A classic example of emergence is in your brain. Individual neurons don’t think, but collectively they produce the emergent phenomenon we call consciousness. Says Morowitz, “the unfolding of life involves many emergences.”
All this is sure to be a matter of contentious debate for a long time. But ours would not be so interesting a world if its ultimate secrets were easily discovered. It took us four billion years to evolve to a point where we could even begin the search.
- Article by Joel Achenbach
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