Liquid Acquisition
Two new scenarios ramp up debate over how
Earth got its water By Ron Cowen
Water is the life of the party on Earth. From shallow creeks to cascading water- falls and raging rivers, it’s
the primal heartbeat of the planet, nurturing a wealth of biological systems
from the very simple to the amazingly
complex. But no one knows for sure how
Earth got this most precious of fluids.
Some researchers contend that the
Earth was born wet. Others assert that
the planet only later acquired the liquid, ferried in from distant reaches of
the solar system. That long-simmering
debate has now reached the boiling point.
Two new ideas for supplying water to
the early Earth have come to the forefront in the past few months. In thrashing out which scenario is more likely,
researchers hope to develop a guide for
finding water-rich and possibly habitable planets beyond the solar system.
During the Earth’s formation, 4. 5 billion years ago, temperatures in the inner
solar system exceeded 400° Celsius — hot
enough to melt lead. So scientists had
assumed that any water would vaporize:
Earth would have been born bone-dry
and would have acquired its water from
elsewhere. For a while, icy comets seemed
a suitable delivery source, but during the
last decade scientists have found that
comet water doesn’t chemically match
