Ocean 'wombs' offer clues to origin of life
Updated: 2005-11-03 05:45
Primordial clay "wombs" that lie scattered around ocean floors played a crucial role in fostering early life on Earth, according to a team of scientists.
The clay structures were found in deep waters, in and around ocean floor volcanic vents called black smokers, so named because they churn out hot black particles from the Earth's crust.
By providing a haven for molecules brought up from the Earth's interior, the wombs protected them from the harsh environment until they formed the most basic building blocks of life, the scientists say. Black smokers form along the edges of mid-ocean ridges. The rich variety of chemicals they emit supports a unique ecosystem including bizarre bacteria and unique species of worms. Scientists believe that these hot, sulphur-rich waters may have been ideal for life to evolve.
Until now researchers have been puzzled as to how molecules could have survived the 300 C temperatures in volcanic vents, but Lynda Williams and her team at Arizona State University in the United States found that lumps of clay that build up on the inside walls of the vents could have captured, then protected, key molecules for around six months. The clay deposits eventually break away and spill out onto the ocean floor, where they break open, releasing the molecules into cool surrounding waters.
Williams's group recreated the high temperature and pressure environment of a black smoker in the laboratory to examine whether organic molecules, the building blocks of life, could grow on various types of clay surface.
"We simulated the reactants that we know can exist in black smoker environments, to see what organic compounds would form in nature," she said. Six weeks into the experiment they discovered that one type of clay mineral, known as smectite, helped organic molecules to survive.
Smectite owes its protective properties to the layers of silicate it is formed from, allowing it to expand easily and let water, ions and molecules to flow inside. "It is a bit like a peanut butter and jelly sandwich," said Williams. "The bread slices are the silicate layers, the sticky peanut butter represents the ions that are attracted to the bread and the jelly is like the organic compounds." The rich chemical soup that rises through black smoker chimneys has all the right ingredients to form simple organic compounds, such as methanol. Williams and her colleagues believe that clay stuck to the vent walls eventually gets pushed out of the chimney by flowing water, carrying the molecules inside to a safer place.
"If the organic compounds are released into cooler ocean water, which it is less acidic, some molecules might survive," she said.
Similar womb-like structures may also exist on other planets.
(China Daily 11/03/2005 page1)