Earth's Water Likely Came from Very Early Asteroid Strikes
By Mike Wall, Senior Writer | October 25, 2013 11:55am ET
Earth got most of its water from asteroid impacts nearly 4.6
billion years ago, shortly after the solar system first took shape,
a new study suggests.
Researchers studying a meteorite that fell to Earth in 2000
found evidence that water in its parent asteroid disappeared
soon after the space rock formed, when its insides were still
warm. Asteroids that slammed into Earth several hundred
million years after the solar system's birth were thus probably
relatively dry, scientists said.
"So, our results suggest that the water [was] supplied to Earth in the period when planets formed
rather than the period of late heavy bombardment from 4.1 billion years to 3.8 billion years ago,"
study lead author Yuki Kimura, of Tohoku University in Japan, told LiveScience via email.
Kimura and his colleagues analyzed the Tagish Lake meteorite, which landed in Canada's Yukon
Territory in January 2000. Scientists think this rock — a type of meteorite known as a carbonaceous
chondrite — is a piece of an asteroid that originated in the main belt between Mars and Jupiter.
Researchers used a
transmission
electron microscope
to observe tiny
particles of
magnetite in the
Tagish Lake
meteorite. Credit: Y.
Kimura & K.
Yamamoto.
The scientists used a transmission electron
microscope to observe tiny particles of magnetite,
which arranged themselves within the meteorite
into three-dimensional "colloidal crystals."
These crystals can be formed during the
sublimation of water — the transition of the material
directly from ice to vapor — but not during freezing,
Kimura said. This implies that the parent asteroid's
bulk water disappeared in the early stages of the solar system's
formation, before the space rock's innards had a chance to cool down,
he added.
Other studies have also found support for very early water delivery to Earth. For example, a paper
published this May in the journal Science found that water on the moon and Earth come from the
same source.
The simplest explanation for this latter observation, researchers say, is that Earth was already wet
by about 4.5 billion years ago, when a planet-size body is believed to have smashed into our planet,
ejecting a huge amount of debris that eventually coalesced into the moon.
In addition to water, impacts likely delivered to the young Earth organic molecules — the carboncontaining building blocks of life as we know it. Indeed, the colloidal crystals in the Tagish Lake
meteorite have an organic layer on their surface, Kimura said.
"Further analysis might give us some information about evolution of organic molecules in the early
solar system," he said.
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Originally published on LiveScience