Impact events
and meteorite strikes are often associated with mass extinctions and widespread
devastation. But, despite this destructive reputation, impact events may have
played a role in the evolution of life, according to several new studies.
A vein of the phosphorus-bearing mineral schreibersite cuts through this iron
meteorite. Phosphorus from meteorites may have contributed to the origin of
life in the early stages of Earth’s history. Image courtesy of Dante Lauretta
and Matt Pasek.
In the so-called primordial soup experiments of the early 1950s, researchers
produced the basic ingredients for life — amino acids and simple organic
molecules — in the laboratory. In the 1960s, scientists discovered that
certain types of meteorites contain amino acids and other fundamental organic
compounds. The explanation of how amino acids evolve into complex proteins and
eventually into living organisms, however, remains elusive.
One problem is producing RNA, a precursor to DNA that is capable of self-replication.
The steps in creating RNA are unclear, but most of the necessary raw materials
and elements are readily available at Earth’s surface — except phosphorus.
Dante Lauretta and Matt Pasek at the University of Arizona say that meteorites
could have provided the phosphorus needed to form complex biomolecules.
In a talk on Aug. 24 at the American Chemical Society’s national meeting
in Philadelphia, Pa., Pasek presented research showing that iron meteorites,
containing the rare phosphate mineral schreibersite, release their phosphorus
in normal distilled water at room temperature. On early Earth, the high concentration
of phosphorus surrounding these meteorites as they sat on the surface of Earth
in pools of water may have contributed to the formation of complex molecules
like RNA, Pasek says.
Other research by planetary geologist Ralph Lorenz, also at the University of
Arizona, suggests that the conditions necessary for primitive biomolecules could
be related to the meteorite strikes themselves in addition to any minerals they
may have brought to the planet. In an upcoming issue of Icarus, Lorenz
contends that asteroid impacts on Saturn’s largest moon, Titan, may have
temporarily melted parts of its frozen surface — opening the door for early
organic molecules.
“There is organic muck raining down from Titan’s atmosphere,”
Lorenz says, “and if you add water, you very quickly begin producing amino
acids.” Scientists are interested in Titan because its thick, hydrocarbon-rich
atmosphere might be similar to Earth’s early atmosphere.
In Lorenz’s model, an impact melt resulting from a large meteorite could
last more than 10,000 years. Smaller impact melts might last hundreds to thousands
of years. “This happened throughout Titan’s history,” Lorenz
says. “It presents a series of very interesting experiments in pre-biotic
compounds.”
A similar scenario could play out on Earth, but Lorenz is hesitant to say meteorites
really benefited early life. “Life may have started very early on Earth,
but it was getting pounded by so many impacts that they may have hurt life or
kept it from getting going,” he says. “There is no evidence that the
net effect is positive.”
Jay Chapman
Geotimes contributing writer
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