A Muddy Start
UMaine scientist helps show
how clays may have made animal life on Earth possible
A clay base
While Larry Mayer has earned a reputation as one of the country's
leading experts in marine sediments, his academic training was in
clay mineralogy, a discipline that he largely set aside when he
began his career at the University of Maine in 1976.
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It is, admittedly, a sound that doesn't
translate well into the written word. Expressed in slow succession on
low tide mornings all along the Maine coast, it's the sound a rubber
boot makes when it is drawn from the clinging, clay-laden muds of
coastal Maine by the straining hamstrings of its owner.
For University of Maine oceanographer Larry Mayer, it also is the sound
Mayer has been hip-deep, both literally
and figuratively, in the Gulf of Maine's marine muck for nearly 30
years, unraveling the mysteries of marine sediments with microscope,
boot and shovel since he began his tenure at UMaine's Darling Marine
Center in the 1970s. His research forays have led him to vast flats of
waterlogged goo across Maine and around the world, trudging through slop
and sludge while gaining a deeper understanding of the Earth as it
exists below the seas.
It was the viscous grip of his own local, coastal muds that ultimately
led to his appreciation for the holding power and growing potential
While working on problems facing the clamming industry in mudflats,
Mayer began to more fully appreciate the important connection between
the preservation of organic matter and the presence of clays. He pursued
this connection into the larger Gulf of Maine, and then into sediments
around the world. Through a recent collaboration with geologists from
the University of California - Riverside, his discoveries have been put
into the context of geological time, and may help to explain how
multicellular life on Earth began. Their research was published in
Science earlier this year.
"Ask your average economist what came first kitty litter or kitties?
Likely (he or she will) reply, kitties. In the environment, clays act as
a kind of kitty litter. They cover over and seal in organic matter,"
says Mayer, pointing out the interaction between clays and organic
particles on an electron micrograph. "In the mudflats just beyond the
woods here, our studies showed that the accumulation of clays enabled
the accumulation of organic matter in marine sediments. By burying
organic matter, clays made it possible to increase the levels of oxygen
in the atmosphere."
In other words, if you are breathing, you may have clays to thank. From
his woodsy office laboratory tucked away in a corner of UMaine's Darling
Marine Center in Walpole, Maine, Mayer explained that the increase in
clay deposition that began more than 500 million years ago may have
tipped the balance between the production of oxygen by plants through
photosynthesis and the consumption of oxygen by single-celled microbes,
transforming the Earth from a relatively harsh and uninviting place for
animals to a fully oxygenated Eden where multicellular life could
Mayer is the first to admit that he is not much of a geologist. With
nearly 30 years of oceanographic science under his belt as a UMaine
researcher and professor, he is much more at home solving the puzzles of
the present day ocean than pursuing the mysteries of the Earth's distant
past. However, in his own college days, Mayer was formally trained as a
clay mineralogist. He took the opportunity to return to his geological
roots when he agreed to collaborate with University of California -
Riverside geologists Martin Kennedy, who led the research.
"Larry made some of the original observations on the mechanisms in
modern sediments that this research is based on," says Kennedy, who was
joined on the study by UCR's Mary Droser and David Mrofka; and David
Pevear. "I'm interested in the longer-term implications how things
changed in geological time. We met at some sort of meeting in
Washington, and he was very enthusiastic about the geology involved."
Kennedy and Mayer's casual discussions soon evolved into a globetrotting
tour of the world's hot spots for very old sedimentary rocks. As the
research team collected samples from critical sites in locales as
diverse as Australia, China and Norway, their goal was to test their
idea that the Earth started making clays in abundance prior to the
evolution of animals.
The layers of sediment act as a tape recorder of Earth's history, says
Mayer. The trick was to find the most complete version of that tape. The
University of California - Riverside geologists were able to locate
thick successions of rock that could integrate the discards of whole
continents, across big space and time scales. By studying the
composition of those rocks, the researchers found that clays came into
the geological record on a worldwide scale between 1 billion and 1.5
billion years ago, during the Late Proterozoic.
Thus, clays arose just before the earliest proliferation of
multicellular animal life a strange assemblage of Precambrian
creatures known as the Ediacaran fauna. As with any scientific enigma,
the hows and whys of the Ediacaran explosion depend heavily on the
wheres and whens. Mayer and Kennedy believe that the amazing
proliferation of multicellular marine life during the Ediacaran was made
possible by the holding power of clays.
But what made the clays? As it turns out, timing of the global increase
in clay deposition fits into a time when new forms of life were believed
to spread across the early Earth's terrestrial landscape.
It is thought that fungi, and maybe mosses and liverworts, first started
become common on the Earth around 600 million800 million years ago.
Fungi would be very interesting additions to the landscape, because they
add new chemicals that are very good at breaking down minerals and
accelerating the weathering process that creates clays. The evolution of
these organisms probably brought about rich, biotic soils that are
essentially clay factories.
Much of the output of these clay factories made its way to the oceans in
the roiling waters of ancient rivers and streams, along with other types
of sediments and increasing amounts of organic matter. As plants
contributed to the atmosphere's oxygen, some of the organic matter that
they also created was sealed off by clay particles from the bacteria and
other organisms that would otherwise break it down using their
oxygen-fueled metabolic processes.
"Oxygen is just a waste product of making organic matter, and it's the
job of respiring organisms to use that oxygen to break organic matter
down again. It's a very efficient recycling system," says Mayer. "So, in
order to get more oxygen to stay in the atmosphere, you have to sneak
organic matter out of the equation, and clay is very good at doing that.
The increase in clays may have been the critical step in increasing
oxygen in the atmosphere. There would be no opportunity for
multicellular animals to evolve without that oxygen."
In other words, you couldn't get to kitties without first making the
"This research speaks to one of the big questions, if not the biggest
question, in geobiology: Why did animal life arise on Earth and what
geological conditions make life possible?" says Kennedy. "The natural
extension of that question is to ask what needs to happen on other
planets for life to exist. It really shows how amazing our planet is and
how dependent we are on the incredibly complex series of linkages
between geological and biological processes."
Indeed, much of the research was funded by NASA. By providing insights
into the complex processes that allowed multicellular animals to develop
and thrive on Earth, the research done by Kennedy and Mayer will help
NASA scientists as they examine the geology of other planets.
NASA hopes to use the information to better understand the types of
conditions that can lead to an environment capable of supporting life on
other planets. The information may help NASA researchers as they look at
new directions for the nation's space program.
Mayer's interests are a little more down to Earth. He plans to continue
his investigation into the nature of clays' interactions with organic
matter and other particles. By developing a better understanding of why
clays are so effective at protecting organic particles from bacteria and
other organisms, Mayer hopes to gain new insights into the basic
geochemical processes that make the Earth such a dynamic and
by David Munson
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