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A Muddy Start

Illustration by Carol Nichols

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 of inspiration.

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 — of clay.

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 flourish.

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 to  become common on the Earth around 600 million–800 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 kitty litter.

"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 hospitable — planet.

by David Munson
May-June, 2006

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