February 3rd 06, 05:43 PM
http://www.newsroom.ucr.edu/cgi-bin/display.cgi?id=1235
UC Riverside Researchers Identify Clay as Major Contributor to
Oxygen that Enabled Early Animal Life
Study suggests steps a planet must go through for complex animal life
to arise
UC Riverside
February 2, 2006
RIVERSIDE, Calif. - Clay made animal life possible on Earth, a UC
Riverside-led study finds. A sudden increase in oxygen in the Earth's
recent geological history, widely considered necessary for the
expansion
of animal life, occurred just as the rate of clay formation on the
Earth's surface also increased, the researchers report.
"Our study shows for the first time that the initial soils covering the
terrestrial surface of Earth increased the production of clay minerals
and provided the critical geochemical processes necessary to oxygenate
the atmosphere and support multicellular animal life," said Martin
Kennedy an associate professor of sedimentary geology and geochemistry
at UCR, who led the study.
Study results appear in the Feb. 2 issue of Science Express, which
provides electronic publication of selected Science papers in advance
of
print.
Analyzing old sedimentary rocks, the researchers found evidence of an
increase in clay mineral deposition in the oceans during a 200 million
year period that fell between 1.1 to 0.54 billion years ago - a stretch
of time known as the late Precambrian when oxygen suddenly increased in
the Earth's atmosphere. The increases in clay formation and oxygen
shortly preceded - in geological time - the first animal fossils about
600 million years ago.
"This study shows how we can use principles developed from the study of
modern environments to understand the very complex origin of life on
our
planet - studying a time in history that has left us only a scanty
record of its conditions," said Lawrence M. Mayer, a professor of
oceanography at the University of Maine and a co-author of the Science
paper.
Clay minerals form in soils through biological interactions with
weathering rocks and are then eroded and flushed to the sea, where they
are deposited as mud. Because clay minerals are chemically reactive,
they attract and absorb organic matter in ocean water, and physically
shelter and preserve it.
The UCR-led study emphasizes the possibility that colonization of the
land surface by a primitive terrestrial ecosystem (possibly involving
fungi) accelerated clay formation, as happens in modern soils. Upon
being washed down to the sea, the clay minerals were responsible for
preserving more organic matter in marine sediments than had been the
case in the absence of clays. Organic matter preservation results in an
equal portion of oxygen released to the atmosphere through the chemical
reaction of photosynthesis. Thus an increase in the burial of organic
carbon made it possible for more oxygen to escape into the atmosphere,
the researchers posit.
"One of the things we least understand is why animals evolved so late
in
Earth history," Kennedy said. "Why did animals wait until the eleventh
hour, whereas evidence for more primitive life dates back to billions
of
years? One of the best bets to explain the difference is an increase in
oxygen concentration in the atmosphere, which is necessary for animal
life and was likely too low through most of Earth's history."
To establish a change in clay abundance during the late Precambrian,
the
researchers studied thick sections of ancient sedimentary rocks in
Australia, China and Scandinavia, representing a history of hundreds of
millions of years, to identify when clay minerals increased in the
sediment from almost nothing to modern depositional levels.
"We predicted we would only find a significant percentage of clay
minerals in sediments toward the end of the Precambrian, when complex
life arose, while earlier sediments would have less clay content,"
Kennedy said. "This test is easier than it sounds. Because clay
minerals
make up the bulk of sediment deposited today, we are saying that it
should be largely absent in ancient rocks. And this is just what one
finds."
The study attracted the attention of the National Aeronautics and Space
Administration during the proposal stage, and the agency helped fund
the
research.
"NASA is interested in what conditions to look for on other planets
that
might lead to the arrival of life," Kennedy said. "What are the
processes? Using earth as our most detailed study site, what are the
necessary steps a planet needs to go through to enable complex animal
life to arise? If oxygen is the metabolic pathway, then we need to know
what conditions have to allow for that to happen. The geologic record
provides us with a record of these steps that occurred on Earth."
UCR"s Mary Droser and David Mrofka; and David Pevear collaborated on
the study, which was supported also by the National Science Foundation.
UC Riverside Researchers Identify Clay as Major Contributor to
Oxygen that Enabled Early Animal Life
Study suggests steps a planet must go through for complex animal life
to arise
UC Riverside
February 2, 2006
RIVERSIDE, Calif. - Clay made animal life possible on Earth, a UC
Riverside-led study finds. A sudden increase in oxygen in the Earth's
recent geological history, widely considered necessary for the
expansion
of animal life, occurred just as the rate of clay formation on the
Earth's surface also increased, the researchers report.
"Our study shows for the first time that the initial soils covering the
terrestrial surface of Earth increased the production of clay minerals
and provided the critical geochemical processes necessary to oxygenate
the atmosphere and support multicellular animal life," said Martin
Kennedy an associate professor of sedimentary geology and geochemistry
at UCR, who led the study.
Study results appear in the Feb. 2 issue of Science Express, which
provides electronic publication of selected Science papers in advance
of
print.
Analyzing old sedimentary rocks, the researchers found evidence of an
increase in clay mineral deposition in the oceans during a 200 million
year period that fell between 1.1 to 0.54 billion years ago - a stretch
of time known as the late Precambrian when oxygen suddenly increased in
the Earth's atmosphere. The increases in clay formation and oxygen
shortly preceded - in geological time - the first animal fossils about
600 million years ago.
"This study shows how we can use principles developed from the study of
modern environments to understand the very complex origin of life on
our
planet - studying a time in history that has left us only a scanty
record of its conditions," said Lawrence M. Mayer, a professor of
oceanography at the University of Maine and a co-author of the Science
paper.
Clay minerals form in soils through biological interactions with
weathering rocks and are then eroded and flushed to the sea, where they
are deposited as mud. Because clay minerals are chemically reactive,
they attract and absorb organic matter in ocean water, and physically
shelter and preserve it.
The UCR-led study emphasizes the possibility that colonization of the
land surface by a primitive terrestrial ecosystem (possibly involving
fungi) accelerated clay formation, as happens in modern soils. Upon
being washed down to the sea, the clay minerals were responsible for
preserving more organic matter in marine sediments than had been the
case in the absence of clays. Organic matter preservation results in an
equal portion of oxygen released to the atmosphere through the chemical
reaction of photosynthesis. Thus an increase in the burial of organic
carbon made it possible for more oxygen to escape into the atmosphere,
the researchers posit.
"One of the things we least understand is why animals evolved so late
in
Earth history," Kennedy said. "Why did animals wait until the eleventh
hour, whereas evidence for more primitive life dates back to billions
of
years? One of the best bets to explain the difference is an increase in
oxygen concentration in the atmosphere, which is necessary for animal
life and was likely too low through most of Earth's history."
To establish a change in clay abundance during the late Precambrian,
the
researchers studied thick sections of ancient sedimentary rocks in
Australia, China and Scandinavia, representing a history of hundreds of
millions of years, to identify when clay minerals increased in the
sediment from almost nothing to modern depositional levels.
"We predicted we would only find a significant percentage of clay
minerals in sediments toward the end of the Precambrian, when complex
life arose, while earlier sediments would have less clay content,"
Kennedy said. "This test is easier than it sounds. Because clay
minerals
make up the bulk of sediment deposited today, we are saying that it
should be largely absent in ancient rocks. And this is just what one
finds."
The study attracted the attention of the National Aeronautics and Space
Administration during the proposal stage, and the agency helped fund
the
research.
"NASA is interested in what conditions to look for on other planets
that
might lead to the arrival of life," Kennedy said. "What are the
processes? Using earth as our most detailed study site, what are the
necessary steps a planet needs to go through to enable complex animal
life to arise? If oxygen is the metabolic pathway, then we need to know
what conditions have to allow for that to happen. The geologic record
provides us with a record of these steps that occurred on Earth."
UCR"s Mary Droser and David Mrofka; and David Pevear collaborated on
the study, which was supported also by the National Science Foundation.