Origin of Life on Earth May Have Begun with Tiny Atmospheric Droplets

An international team of researchers has
proposed a new theory that aerosol particles in the ancient atmosphere
may have played a role in generating the chemical building blocks
for life on Earth. Indeed, they say, the aerosols may have had
many characteristics of a primitive form of "cell".

The study will be published in the Proceedings of the National Academy
of Sciences by scientists from the National Oceanic and
Atmospheric Administration’s Aeronomy
Laboratory in Boulder, Colo., Oxford
University, England, and the University
of Colorado at Boulder.

Researchers Adrian Tuck of NOAA,
Christopher Dobson of Oxford, and Barney Ellison and Veronica
Vaida of the University of Colorado suggest that aerosol particles,
which are produced by waves at the ocean surface, could have
picked up an organic outer coating as the bubbles burst in the
air. Aloft in the atmosphere for days, months or even longer,
the particles may have been like minuscule "chemical reaction
chambers," exposing their interior contents to a wide range
of temperatures, humidities, and sunlight exposures. Through
evaporation, simple organic materials inside the aerosols could
have become more concentrated. "Encounters with other atmospheric
particles, such as those derived from meteorites, could have
enabled the particles to pick up trace amounts of metallic species
that facilitated chemical reactions within."

This combination of factors could have
promoted formation of the more complex organic molecules that
are fundamental to life, such as proteins and nucleic acids.
The lack of oxygen and ozone in the early atmosphere would have
aided the process.

The new theory helps to explain many aspects
of the simplest organisms of ancient Earth. The authors show
that aerosol particles have many characteristics that are similar
to bacteria and other single-celled organisms. For example, they
are similar in size, they possess a watery solution in their
interior, and their salinity values differ from those of the
ocean.

Further, the new theory shows how some
of the more unusual aspects of cells may have developed. For
example, the presence of a double outer membrane in cells has
been difficult to explain. The new study shows how the airborne
particles would have formed two outer layers of organic material,
one layer when they first left the ocean surface and a second
layer when they returned from the atmosphere back to the ocean.

Oxford University’s Dobson says that coagulation
and division of the particles could be viewed as an early analog
of reproduction and replication processes in cells. The large
populations of aerosols, recycling over geological time, would
have allowed natural selection of successful chemical populations
of molecules to evolve.

According to Adrian Tuck, the study was
sparked by recent NOAA observations that individual atmospheric
particles are not just seawater or sulphuric acid, but instead
contain a large amount of organic material. In theorizing how
the organic material could have gotten into the atmosphere, the
researchers conceived of the oceanic mechanism and the possible
connection to precursors of living systems on Earth.

Many previous theories of the origin of
single-celled life forms have suggested that the prebiotic chemistry
occurred in terrestrial waters, such as tidal pools, but questions
had remained about how sufficient energy and concentrations of
chemicals could have been achieved. It was also not readily apparent
how single-celled organisms could have formed, or why they had
the size they did. The authors of today’s study state their new
atmospheric aerosol theory helps to answer many key questions,
but that experiments in large reaction chambers could provide
useful tests of their ideas.

Members of the media can obtain an advance
copy of the paper by calling

(202) 334-2138.