Did droplets high in the atmosphere give birth to the first living cells?
LIFE may have begun not in the sea but in tiny water droplets drifting high in the sky. Thrown up by ocean waves, these droplets could have provided just the conditions needed for complex molecules to form.
This radical theory, proposed by an international team of researchers at the Royal Meteorological Society's millennium conference in Cambridge this week, could explain long-standing mysteries about the origin of life, such as how cells got their membranes and how simple organic molecules became concentrated enough to join together to form large, complex ones.
The theory arose when Adrian Tuck of the National Oceanic and Atmospheric Administration in Boulder, Colorado, noticed the work of Daniel Murphy, also of NOAA. Murphy had discovered that instead of being just seawater, up to half the material in the droplets in today's atmosphere is organic matter.
Tuck and his colleagues Veronica Vaida and Barney Ellison of the University of Colorado realised that the droplets, or aerosol particles, contain so much organic material because they pick up a lipid coating from the film of oily molecules on the surface of the ocean. "They look like protocells, with a layer of organic material on the outside," he says.
While the droplets are floating in the upper atmosphere, they often fuse with other particles, which might contain substances such as iron and nickel derived from meteorites burning up in the atmosphere. "Aerosols in the stratosphere can last up to a year," says Murphy. "They have lots of time to pick up different things."
As the water in the droplets evaporates, the diverse substances within them become concentrated. This, combined with the energy provided by the strong sunlight, encourages chemical reactions. That could explain how the simple organic molecules on the primordial Earth came to form complex chemicals such as DNA and proteins.