Science News
ScienceDaily (June 14, 2008) — A new analysis of ancient minerals
called zircons suggests that a harsh climate may have scoured and
possibly even destroyed the surface of the Earth's earliest continents.
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Earth & Climate
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Geology
Earth Science
Environmental Issues
Climate
Near-Earth Object Impacts
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Reference
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Sedimentary rock
Metamorphic rock
Continental crust
Crust (geology)
Zircons, the oldest known materials on Earth, offer a window in time back as far as 4.4 billion
years ago, when the planet was a mere 150 million years old. Because these crystals are
exceptionally resistant to chemical changes, they have become the gold standard for
determining the age of ancient rocks, says University of Wisconsin-Madison geologist John
Valley.
Valley previously used these tiny mineral grains - smaller than a speck of sand - to show that
rocky continents and liquid water formed on the Earth much earlier than previously thought,
about 4.2 billion years ago.
In a new paper recently published online in the journal Earth and Planetary Science Letters, a
team of scientists led by UW-Madison geologists Takayuki Ushikubo, Valley and Noriko Kita
show that rocky continents and liquid water existed at least 4.3 billion years ago and were
subjected to heavy weathering by an acrid climate.
Ushikubo, the first author on the new study, says that atmospheric weathering could provide an
answer to a long-standing question in geology: why no rock samples have ever been found
dating back to the first 500 million years after the Earth formed.
"Currently, no rocks remain from before about 4 billion years ago," he says. "Some people
consider this as evidence for very high temperature conditions on the ancient Earth."
Previous explanations for the missing rocks have included destruction by barrages of meteorites
and the possibility that the early Earth was a red-hot sea of magma in which rocks could not
form.
The current analysis suggests a different scenario. Ushikubo and colleagues used a
sophisticated new instrument called an ion microprobe to analyze isotope ratios of the element
lithium in zircons from the Jack Hills in western Australia. By comparing these chemical
fingerprints to lithium compositions in zircons from continental crust and primitive rocks similar
to the Earth's mantle, they found evidence that the young planet already had the beginnings of
continents, relatively cool temperatures and liquid water by the time the Australian zircons
formed.
"At 4.3 billion years ago, the Earth already had habitable conditions," Ushikubo says.
The zircons' lithium signatures also hold signs of rock exposure on the Earth's surface and
breakdown by weather and water, identified by low levels of a heavy lithium isotope.
"Weathering can occur at the surface on continental crust or at the bottom of the ocean, but the
[observed] lithium compositions can only be formed from continental crust," says Ushikubo.
The findings suggest that extensive weathering may have destroyed the Earth's earliest rocks,
he says.
"Extensive weathering earlier than 4 billion years ago actually makes a lot of sense," says
Valley. "People have suspected this, but there's never been any direct evidence."
Carbon dioxide in the atmosphere can combine with water to form carbonic acid, which falls as
acid rain. The early Earth's atmosphere is believed to have contained extremely high levels of
carbon dioxide - maybe 10,000 times as much as today.
"At [those levels], you would have had vicious acid rain and intense greenhouse [effects]. That
is a condition that will dissolve rocks," Valley says. "If granites were on the surface of the Earth,
they would have been destroyed almost immediately - geologically speaking - and the only
remnants that we could recognize as ancient would be these zircons."
Other co-authors on the paper include Aaron Cavosie of the University of Puerto Rico, Simon
Wilde of the Curtin University of Technology in Australia and Roberta Rudnick of the University
of Maryland.
__________________________________________________
New Thermometer Confirms Wet Conditions On Earliest
Earth
ScienceDaily (June 1, 2005) — Using a newly developed thermometer
made of zircon, researchers have found evidence that environmental
conditions on early Earth, within 200 million years of the solar system's
formation, were characterized by liquid-water oceans and continental
crust similar to those of the present day.
The findings are reported in the May 6 issue of the journal Science.
"Our data support recent theories that Earth began a pattern of crust formation, erosion, and
sediment recycling as early in its evolution as 4.35 billion years ago, which contrasts with the
hot, violent environment envisioned for our young planet by most researchers and opens up the
possibility that life got a very early foothold," said Bruce Watson, a geochemist at Rensselaer
Polytechnic Institute (RPI) in Troy, New York.
Watson collaborated with scientist Mark Harrison, affiliated with the Australian National
University and UCLA, on the research. The work was also supported by the Australian
Research Council and NASA's Astrobiology Institute.
Watson and Harrison developed a new thermometer that measures the titanium content of
zircon crystals to determine their crystallization temperature. Zircons are tiny crystals embedded
in rock and are the oldest known materials on Earth. Zircons pre-date by 400 million years the
oldest known rocks on Earth. These ancient crystals provide researchers with a window into the
earliest history of the Earth, and have been used to date the assembly and movement of
continents and oceans.
"Zircons allow us to go farther back in geologic time because they survive processes that rocks
do not," said Watson. "Although they are only a fraction of a millimeter in size, zircons hold a
wealth of information about the very earliest history of Earth."
"This study solidifies the importance of zircons as time capsules of processes happening at the
earliest time in Earth history," said Sonia Esperanca, program director in NSF's division of earth
sciences, which funded the research.
According to Watson, the research provides important information and a new technique for
making additional discoveries about the first eon of Earth's history, the Hadean eon, a time
period about which little is known.
Using the new thermometer, the scientists analyzed zircons ranging in age from 4 billion to 4.35
billion years from the Jack Hills area of Western Australia. The temperature data supports the
existence of wet, minimum-melting conditions within 200 million years of solar system formation,
according to the researchers.
The researchers say the thermometer provides clear distinction among zircons crystallized in
the mantle, in granites, and during metamorphism, thereby giving consistent information about
the conditions on Earth during those crystals' formation.
Watson describes his research as "materials science of the Earth," because it involves
designing and executing laboratory experiments at the high temperatures and pressures found
in the Earth's deep crust and upper mantle.
ScienceDaily
Ancient Mineral Shows Early Earth Climate Tough On Continents
ScienceDaily (June 14, 2008) — A new analysis of ancient minerals
called zircons suggests that a harsh climate may have scoured and
possibly even destroyed the surface of the Earth's earliest continents.
Reference




Sedimentary rock
Metamorphic rock
Continental crust
Crust (geology)
Zircons, the oldest known materials on Earth, offer a window in time back as far as 4.4 billion
years ago, when the planet was a mere 150 million years old. Because these crystals are
exceptionally resistant to chemical changes, they have become the gold standard for
determining the age of ancient rocks, says University of Wisconsin-Madison geologist John
Valley.
Valley previously used these tiny mineral grains - smaller than a speck of sand - to show that
rocky continents and liquid water formed on the Earth much earlier than previously thought,
about 4.2 billion years ago.
In a new paper recently published online in the journal Earth and Planetary Science Letters, a
team of scientists led by UW-Madison geologists Takayuki Ushikubo, Valley and Noriko Kita
show that rocky continents and liquid water existed at least 4.3 billion years ago and were
subjected to heavy weathering by an acrid climate.
Ushikubo, the first author on the new study, says that atmospheric weathering could provide an
answer to a long-standing question in geology: why no rock samples have ever been found
dating back to the first 500 million years after the Earth formed.
"Currently, no rocks remain from before about 4 billion years ago," he says. "Some people
consider this as evidence for very high temperature conditions on the ancient Earth."
Previous explanations for the missing rocks have included destruction by barrages of meteorites
and the possibility that the early Earth was a red-hot sea of magma in which rocks could not
form.
The current analysis suggests a different scenario. Ushikubo and colleagues used a
sophisticated new instrument called an ion microprobe to analyze isotope ratios of the element
lithium in zircons from the Jack Hills in western Australia. By comparing these chemical
fingerprints to lithium compositions in zircons from continental crust and primitive rocks similar
to the Earth's mantle, they found evidence that the young planet already had the beginnings of
continents, relatively cool temperatures and liquid water by the time the Australian zircons
formed.
"At 4.3 billion years ago, the Earth already had habitable conditions," Ushikubo says.
The zircons' lithium signatures also hold signs of rock exposure on the Earth's surface and
breakdown by weather and water, identified by low levels of a heavy lithium isotope.
"Weathering can occur at the surface on continental crust or at the bottom of the ocean, but the
[observed] lithium compositions can only be formed from continental crust," says Ushikubo.
The findings suggest that extensive weathering may have destroyed the Earth's earliest rocks,
he says.
"Extensive weathering earlier than 4 billion years ago actually makes a lot of sense," says
Valley. "People have suspected this, but there's never been any direct evidence."
Carbon dioxide in the atmosphere can combine with water to form carbonic acid, which falls as
acid rain. The early Earth's atmosphere is believed to have contained extremely high levels of
carbon dioxide - maybe 10,000 times as much as today.
"At [those levels], you would have had vicious acid rain and intense greenhouse [effects]. That
is a condition that will dissolve rocks," Valley says. "If granites were on the surface of the Earth,
they would have been destroyed almost immediately - geologically speaking - and the only
remnants that we could recognize as ancient would be these zircons."
Other co-authors on the paper include Aaron Cavosie of the University of Puerto Rico, Simon
Wilde of the Curtin University of Technology in Australia and Roberta Rudnick of the University
of Maryland.
Story Source:
The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by
University of
Wisconsin-Madison.
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University of Wisconsin-Madison (2008, June 14). Ancient Mineral Shows Early Earth Climate Tough On Continents. ScienceDaily. Retrieved June
22, 2010, from http://www.sciencedaily.com /releases/2008/06/080613170202.htm
Note: If no author is given, the source is cited instead.
A timeline shows the geological context of Jack Hills zircons, ancient minerals that formed when the Earth was less than 500 million years old.
(Credit: Illustration: Andree Valley)
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Mineral Kingdom Has Co-Evolved With Life, Scientists
Find
ScienceDaily (Nov. 14, 2008) — Evolution isn't just for living
organisms. Scientists at the Carnegie Institution have found that the
mineral kingdom co-evolved with life, and that up to two thirds of the
more than 4,000 known types of minerals on Earth can be directly or
indirectly linked to biological activity.
The finding, published in American Mineralogist, could aid scientists in the search for life on
other planets.
Robert Hazen and Dominic Papineau of the Carnegie Institution's Geophysical Laboratory, with
six colleagues, reviewed the physical, chemical, and biological processes that gradually
transformed about a dozen different primordial minerals in ancient interstellar dust grains to the
thousands of mineral species on the present-day Earth. (Unlike biological species, each mineral
species is defined by its characteristic chemical makeup and crystal structure.)
"It's a different way of looking at minerals from more traditional approaches," says Hazen.
"Mineral evolution is obviously different from Darwinian evolution—minerals don't mutate,
reproduce or compete like living organisms. But we found both the variety and relative
abundances of minerals have changed dramatically over more than 4.5 billion years of Earth's
history."
All the chemical elements were present from the start in the Solar Systems' primordial dust, but
they formed comparatively few minerals. Only after large bodies such as the Sun and planets
congealed did there exist the extremes of temperature and pressure required to forge a large
diversity of mineral species. Many elements were also too dispersed in the original dust clouds
to be able to solidify into mineral crystals.
As the Solar System took shape through "gravitational clumping" of small, undifferentiated
bodies—fragments of which are found today in the form of meteorites—about 60 different
minerals made their appearance. Larger, planet-sized bodies, especially those with volcanic
activity and bearing significant amounts of water, could have given rise to several hundred new
mineral species. Mars and Venus, which Hazen and coworkers estimate to have at least 500
different mineral species in their surface rocks, appear to have reached this stage in their
mineral evolution.
However, only on Earth—at least in our Solar System—did mineral evolution progress to the
next stages. A key factor was the churning of the planet's interior by plate tectonics, the process
that drives the slow shifting continents and ocean basins over geological time. Unique to Earth,
plate tectonics created new kinds of physical and chemical environments where minerals could
form, and thereby boosted mineral diversity to more than a thousand types.
What ultimately had the biggest impact on mineral evolution, however, was the origin of life,
approximately 4 billion years ago. "Of the approximately 4,300 known mineral species on Earth,
perhaps two thirds of them are biologically mediated," says Hazen. "This is principally a
consequence of our oxygen-rich atmosphere, which is a product of photosynthesis by
microscopic algae." Many important minerals are oxidized weathering products, including ores
of iron, copper and many other metals.
Microorganisms and plants also accelerated the production of diverse clay minerals. In the
oceans, the evolution of organisms with shells and mineralized skeletons generated thick
layered deposits of minerals such as calcite, which would be rare on a lifeless planet.
"For at least 2.5 billion years, and possibly since the emergence of life, Earth's mineralogy has
evolved in parallel with biology," says Hazen. "One implication of this finding is that remote
observations of the mineralogy of other moons and planets may provide crucial evidence for
biological influences beyond Earth."
Stanford University geologist Gary Ernst called the study "breathtaking," saying that "the unique
perspective presented in this paper may revolutionize the way Earth scientists regard minerals."
Life basis came from sources beyond the Earth
Published by Ian under Bio-Sciences, News categories on June
30, 2008
Scientists have confirmed for the first time that an important
component of early genetic material which has been found in
meteorite fragments is extraterrestrial in origin. The scientists,
from Europe and the USA, say that their research, published in
the journal Earth and Planetary Science Letters, provides
evidence that life’s raw materials came from sources beyond the
Earth.
The materials they have found include the molecules uracil and
xanthine, which are precursors to the molecules that make up
DNA and RNA, and are known as nucleobases. The team
discovered the molecules in rock fragments of the Murchison
meteorite, which crashed in Australia in 1969. They tested the
meteorite material to determine whether the molecules came from
the solar system or were a result of contamination when the
meteorite landed on Earth. The analysis shows that the
nucleobases contain a heavy form of carbon which could only
have been formed in space. Materials formed on Earth consist of a
lighter variety of carbon.
Lead author Dr Zita Martins, of the Department of Earth Science
and Engineering at Imperial College London, says that the
research may provide another piece of evidence explaining the
evolution of early life. She says: “We believe early life may have
adopted nucleobases from meteoritic fragments for use in genetic
coding which enabled them to pass on their successful features to
subsequent generations.”
Between 3.8 to 4.5 billion years ago large numbers of rocks
similar to the Murchison meteorite rained down on Earth at the
time when primitive life was forming. The heavy bombardment
would have dropped large amounts of meteorite material to the
surface on planets like Earth and Mars.
Co-author Professor Mark Sephton, also of Imperial’s Department
of Earth Science and Engineering, believes this research is an
important step in understanding how early life might have
evolved. He added: “Because meteorites represent left over
materials from the formation of the solar system, the key
components for life — including nucleobases — could be
widespread in the cosmos. As more and more of life’s raw
materials are discovered in objects from space, the possibility of
life springing forth wherever the right chemistry is present
becomes more likely.”