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Meteorites Pummeled
Earth, Delivering Gold
A slew of meteorites pelted Earth some 3.9 billion years
ago -- delivering that gold you may be wearing on your
finger.
An artist's impression of the Earth during the period
of meteorite bombardment 3.9 billion years ago.
Your wedding ring, the gold chain around your neck… even the platinum in
your catalytic converter. For all of these you can thank a slew of
meteorites that pelted Earth around 3.9 billion years ago, says new
research.
Certain metals like gold, platinum, nickel, tungsten and iridium are attracted
to iron, which comprises the Earth's core. So when the Earth first formed
as a molten mass, all of these elements should have migrated to the core,
leaving the outer layers of Earth stripped of its precious metals.
Yet as hopeful '49-ers knew, Earth's crust is laced with these enticing
elements. Geologists have posed several theories to explain this puzzle, but
one suggests that Earth was bombarded with meteorites between 3.8 and
4 billion years ago, studding the early crust with our favorite shiny metals.
These metals then became incorporated into the modern mantle over time.
This idea is supported by the presence of craters on the moon, which date
back to the same time, suggesting that the moon was also hit. Now,
research published today in Nature, provides further evidence in favor of
this explanation.
A team led by Matthias Willbold of the University of Bristol, U.K., sampled
ancient rocks from southwest Greenland that formed some of the Earth's
earliest crust, predating the proposed bombardment, and compared those
with newer rocks from other places representing the modern mantle.
The researchers found distinct differences in the concentrations of
particular tungsten isotopes in each type.
"This is a sort of a time capsule that gave us the possibility to calculate
how much material had to be added to the Earth to satisfy the tungsten
isotopic composition that we find in the Earth today," Willbold said.
"It is so far the best isotopic or geochemical evidence that late
bombardment ever happened," he added.
"Our ability to measure these (isotopes) precisely enough to see these
differences is just opening a totally new window into early planet
formation," said Richard Carlson of the Carnegie Institution of Washington
who has also studied early Earth using isotopes.
The researchers calculated that about half a percent of the present-day
mantle would have been added by meteorites.
"That sounds like not really much, but it's about 300 billion billion tons of
material," Willbold said.
"All the precious metals that we find today -- and probably also water --
have been introduced to the accessible Earth from these late stage
meteorites," he said.
Indeed, the bombardment may even have brought the necessary
conditions for life on Earth.
Carlson explained the early bombardment of meteorites would have been "a
terrible event for life. It probably would have melted the planet, blown off
any existing atmosphere."
But, he adds, "It's possible that this late veneer brought in the goodies
afterward and it brought them in gently enough that they stuck around. I
don't know that it brought in life, but it brought in maybe the constituents
of it: the water, the right kind of surface temperatures, and the
atmosphere that is conducive to life."
Meteorites Pummeled Earth, Delivering Gold : Discovery News
Earth, Delivering Gold
A slew of meteorites pelted Earth some 3.9 billion years
ago -- delivering that gold you may be wearing on your
finger.
An artist's impression of the Earth during the period
of meteorite bombardment 3.9 billion years ago.
Your wedding ring, the gold chain around your neck… even the platinum in
your catalytic converter. For all of these you can thank a slew of
meteorites that pelted Earth around 3.9 billion years ago, says new
research.
Certain metals like gold, platinum, nickel, tungsten and iridium are attracted
to iron, which comprises the Earth's core. So when the Earth first formed
as a molten mass, all of these elements should have migrated to the core,
leaving the outer layers of Earth stripped of its precious metals.
Yet as hopeful '49-ers knew, Earth's crust is laced with these enticing
elements. Geologists have posed several theories to explain this puzzle, but
one suggests that Earth was bombarded with meteorites between 3.8 and
4 billion years ago, studding the early crust with our favorite shiny metals.
These metals then became incorporated into the modern mantle over time.
This idea is supported by the presence of craters on the moon, which date
back to the same time, suggesting that the moon was also hit. Now,
research published today in Nature, provides further evidence in favor of
this explanation.
A team led by Matthias Willbold of the University of Bristol, U.K., sampled
ancient rocks from southwest Greenland that formed some of the Earth's
earliest crust, predating the proposed bombardment, and compared those
with newer rocks from other places representing the modern mantle.
The researchers found distinct differences in the concentrations of
particular tungsten isotopes in each type.
"This is a sort of a time capsule that gave us the possibility to calculate
how much material had to be added to the Earth to satisfy the tungsten
isotopic composition that we find in the Earth today," Willbold said.
"It is so far the best isotopic or geochemical evidence that late
bombardment ever happened," he added.
"Our ability to measure these (isotopes) precisely enough to see these
differences is just opening a totally new window into early planet
formation," said Richard Carlson of the Carnegie Institution of Washington
who has also studied early Earth using isotopes.
The researchers calculated that about half a percent of the present-day
mantle would have been added by meteorites.
"That sounds like not really much, but it's about 300 billion billion tons of
material," Willbold said.
"All the precious metals that we find today -- and probably also water --
have been introduced to the accessible Earth from these late stage
meteorites," he said.
Indeed, the bombardment may even have brought the necessary
conditions for life on Earth.
Carlson explained the early bombardment of meteorites would have been "a
terrible event for life. It probably would have melted the planet, blown off
any existing atmosphere."
But, he adds, "It's possible that this late veneer brought in the goodies
afterward and it brought them in gently enough that they stuck around. I
don't know that it brought in life, but it brought in maybe the constituents
of it: the water, the right kind of surface temperatures, and the
atmosphere that is conducive to life."
Meteorites Pummeled Earth, Delivering Gold : Discovery News