Clay Major Contributor To Oxygen That Enabled Early Animal Life
- Clay Major Contributor To Oxygen That Enabled Early Animal Life
by Staff Writers
Riverside CA (SPX) Feb 03, 2006
A UC Riverside-led study has found that clay made animal life
possible on Earth. 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
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
"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
Martin Kennedy, associate professor in the Department of Earth
Sciences at UCR, led a study that identifies clay as a major
contributor to oxygen that enabled early animal life on Earth.