Science Current Events | Science News | Brightsurf.com
 

Earth's Moving Crust May Occasionally Stop

January 10, 2008
The motion, formation, and recycling of Earth's crust-commonly known as plate tectonics-have long been thought to be continuous processes. But new research by geophysicists suggests that plate tectonic motions have occasionally stopped in Earth's geologic history, and may do so again. The findings could reshape our understanding of the history and evolution of the Earth's crust and continents.

Synthesizing a wide range of observations and constructing a new theoretical model, researchers Paul Silver of the Carnegie Institution of Washington and Mark Behn of the Woods Hole Oceanographic Institution (WHOI) have found evidence that the process of subduction has effectively stopped at least once in Earth's past. Subduction occurs where two pieces of Earth's crust (tectonic plates) collide, and one dives beneath the other back into the interior of the planet.

Most of the major geologic processes on Earth-the formation of continents, the birth of volcanic island arcs, the opening and closing of ocean basins-are driven by tectonic plate motions and intimately linked to subduction and to seafloor spreading. If those processes were shut down, there would likely be a global decrease in earthquakes and volcanism.

Today, the vast majority of subduction occurs around the edges of the Pacific Ocean, which is slowly closing as the Atlantic Ocean opens. In roughly 350 million years, researchers estimate that the Pacific basin will be effectively closed and a new supercontinent will be formed.

Closure of the Pacific basin could shut down most of the Earth's capacity for subduction, unless the process begins somewhere else on the planet. However, there is no evidence that subduction is currently expanding or initiating anywhere else on the planet.

Though such a shutdown defies the prevailing wisdom about plate tectonics, Silver and Behn read the geologic evidence to suggest that just such a dramatic decrease in subduction happened about one billion years ago, after the formation of the supercontinent Rodinia.

Their findings-captured in a paper entitled "Intermittent Plate Tectonics?"-were published in the January 4 issue of the journal Science.

"The scientific community has typically assumed that plate tectonics is an active and continuous process, that new crust is constantly being formed while old crust is recycled," said Behn, an assistant scientist in the WHOI Department of Geology and Geophysics. "But the evidence suggests that plate tectonics may not be continuous. Plates may move actively at times, then stop or slow down, and then start up again."

Behn and Silver started their investigation by considering how the Earth releases heat from its interior over time, also known as "thermal evolution." If you take the rate at which the Earth is releasing heat from its interior today and project that rate backwards in time, you arrive at impossibly high and unsustainable numbers for the heat and energy contained in the early Earth. Specifically, if the planet has been releasing heat at the modern rate for all of its history, then it would have been covered with a magma ocean as recently as one billion years ago.

But we know this is not true, Behn said, because there is geological evidence for past continents and supercontinents, not to mention rocks (ophiolites) on the edges of old plate boundaries that are more than one billion years old.

The Earth cools more quickly during periods of rapid plate motions, as warm material is pulled upward from deep in the Earth's interior and cools beneath spreading ridges.

"If you stir a cup of coffee, it cools faster," said Behn. "That's why people blow on their coffee to get the surface moving."

"It is a similar process within the Earth," Behn added. "If the tectonic plates are moving, the Earth releases more heat and cools down faster. If you don't have those cracked and moving plates, then heat has to get out by diffusing through the solid rock, which is much slower."

Periods of slow or no subduction would help explain how the Earth still has so much heat to release today, since some of it would have been capped beneath the crust.

Silver and Behn conclude their paper by suggesting that there is a cycle to plate tectonics, with periods when the shifting and sliding of the crust is more active and times when it is less so. Rather than being continuous, plate tectonics may work intermittently through Earth history, turning on and off as the planet remakes itself.

The Woods Hole Oceanographic Institution is a private, independent organization in Falmouth, Mass., dedicated to marine research, engineering, and higher education. Established in 1930 on a recommendation from the National Academy of Sciences, its primary mission is to understand the oceans and their interaction with the Earth as a whole, and to communicate a basic understanding of the ocean's role in the changing global environment.

The Carnegie Institution of Washington has been a pioneering force in basic scientific research since 1902. It is a private, nonprofit organization with six research departments throughout the U.S. Carnegie scientists are leaders in plant biology, developmental biology, astronomy, materials science, global ecology, and Earth and planetary science.

Woods Hole Oceanographic Institution


Related Subduction Current Events and Subduction News Articles


Rising above the risk: America's first tsunami refuge
Washington's coast is so close to the seismically active Cascadia Subduction Zone that if a megathrust earthquake were to occur, a tsunami would hit the Washington shoreline in just 25 minutes.

Journey to the Center of the Earth
A UC Santa Barbara geochemist studying Samoan volcanoes has found evidence of the planet's early formation still trapped inside the Earth. Known as hotspots, volcanic island chains such as Samoa can ancient primordial signatures from the early solar system that have somehow survived billions of years.

New study reconstructs mega-earthquakes timeline in Indian Ocean
A new study on the frequency of past giant earthquakes in the Indian Ocean region shows that Sri Lanka, and much of the Indian Ocean, is affected by large tsunamis at highly variable intervals, from a few hundred to more than one thousand years.

Mantle plumes crack continents
In some parts of the Earth, material rises upwards like a column from the boundary layer of the Earth's core and the lower mantel to just below the Earth's crust hundreds of kilometres above.

Study of Chilean quake shows potential for future earthquake
Near real-time analysis of the April 1 earthquake in Iquique, Chile, showed that the 8.2 event occurred in a gap on the fault unruptured since 1877 and that the April event was not what the scientists had expected, according to an international team of geologists.

Studies show movements of continents speeding up after slow 'middle age'
Two studies show that the movement rate of plates carrying the Earth's crust may not be constant over time.

New evidence for oceans of water deep in the Earth
Researchers from Northwestern University and the University of New Mexico report evidence for potentially oceans worth of water deep beneath the United States.

Ancient rocks yield clues about Earth's earliest crust
It looks like just another rock, but what Jesse Reimink holds in his hands is a four-billion-year-old chunk of an ancient protocontinent that holds clues about how the Earth's first continents formed.

Deep earth recycling of the oceanic floor
Scientists from the Magma and Volcanoes Laboratory (CNRS/IRD/Université Blaise Pascal) and the European Synchrotron, the ESRF, have recreated the extreme conditions 600 to 2900 km below the Earth's surface to investigate the melting of basalt in the oceanic tectonic plates.

Great earthquakes, water under pressure, high risk
The largest earthquakes occur where oceanic plates move beneath continents. Obviously, water trapped in the boundary between both plates has a dominant influence on the earthquake rupture process.
More Subduction Current Events and Subduction News Articles

Subduction

Subduction
by Todd Shimoda (Author), L.J.C. Shimoda (Illustrator)


"Shimoda is a consummate storyteller" — Booklist

"Shimoda skillfully weaves (these) tales into the narrative, revealing how past events "continue to affect the island, like aftershocks." Earthquakes are an apt metaphor for the social disruptions on the island, and Shimoda links modern earthquake science, ancient Japanese myths on the origin of earthquakes, and an unforgettable cast of characters to create a suspenseful, richly illustrated novel." — Publishers Weekly

"Husband and wife team Todd and Linda Shimoda’s skills blend seamlessly together to make Subduction a hauntingly beautiful and highly unique novel. The author’s prose and illustrator’s talent give the book a tone and quality that is both rare and memorable." — ForeWord

"Subduction heaves with a...

Subduction Zone

Subduction Zone
by Emily Mcgiffin (Author)


Subduction Zone is a book of meditations on empire — the desires and agendas of empire, and empire’s detritus. From a sweeping panorama of imperial landscapes both classical and modern, it carries us into the troubled natural beauty of the world. Its third and final sequence brings Canadians home, to the manifestations of global technocracy in northwest BC.Whether contemplating rain forests in the Visayan Islands or Edward Burtynsky’s photographs, these poems gaze unflinchingly at the exploitation and upheaval that define several millennia of global politics. Their questions are both urgent and intricate. Who are we individually, collectively, in this era of looming ecological collapse? How do we acknowledge the blood on our hands yet bear witness to the beauty that remains?...

Streetcar to Subduction and Other Plate Tectonic Trips by Public Transport in San Francisco (Special Publications)

Streetcar to Subduction and Other Plate Tectonic Trips by Public Transport in San Francisco (Special Publications)
by Clyde Wahrhaftig (Author)


Published by the American Geophysical Union as part of the Special Publications Series.It is hard to be unaware of the earth in San Francisco. Built on rocky hills, the city is surrounded on three sides by bay and ocean that can be seen from nearly everywhere within it. Precipitous cliffs face the city from across the Golden Gate, and the skyline to the north, east, and south is dominated by mountains. Occasional tremors from the San Andreas and related faults nearby remind us that the earth here is active. Until recently the rocks so abundantly exposed in San Francisco baffled geologists. Jumbled together without apparent order and lacking visible fossils, they defied explanation. The theory of plate tectonics has changed all that. We now have an explanation for the origin of the rocks...

Assembling California

Assembling California
by John McPhee (Author)


At various times in a span of fifteen years, John McPhee made geological field surveys in the company of Eldridge Moores, a tectonicist at the University of California at Davis. The result of these trips is Assembling California, a cross-section in human and geologic time, from Donner Pass in the Sierra Nevada through the golden foothills of the Mother Lode and across the Great Central Valley to the wine country of the Coast Ranges, the rock of San Francisco, and the San Andreas family of faults. The two disparate time scales occasionally intersect—in the gold disruptions of the nineteenth century no less than in the earthquakes of the twentieth—and always with relevance to a newly understood geologic history in which half a dozen large and separate pieces of country are seen to have...

Subduction Zone Magmatism (Frontiers in Earth Sciences)

Subduction Zone Magmatism (Frontiers in Earth Sciences)
by Yoshiyuki Tatsumi (Author), Steve Eggins (Author)


Subduction zones are major sites of volcanism on the Earth. As one crustal plate sinks or is pushed beneath another, hot magma is produced and the resultant magma flux is fundamental to both the thermal evolution and chemical differentiation of the mantle and the Earth itself. To understand these evolutionary processes, we need to understand the physical and chemical consequences of all aspects of the subduction process. In this book, the authors present a simple, current and comprehensive model that explains the dominant geological processes at work in subduction zones. Structuring the book around the model, the authors describe the physical characteristics and geochemical dynamics of subduction zones, arc magma generation, and the dynamics and flow in the mantle. Students and...

Subduction Zone Geodynamics (Frontiers in Earth Sciences)

Subduction Zone Geodynamics (Frontiers in Earth Sciences)
by Serge Lallemand (Editor), Francesca Funiciello (Editor)


Subduction is a major process that plays a first-order role in the dynamics of the Earth. The sinking of cold lithosphere into the mantle is thought by many authors to be the most important source of energy for plates driving forces. It also deeply modifies the thermal and  chemical structure of the mantle, producing arc volcanism and is responsible for the release of most of the seismic energy on Earth. There has been considerable achievements done during the past decades regarding the complex interactions between the various processes acting in subduction zones. This volume contains a collection of contributions that were presented in June 2007 in Montpellier (France) during a conference that gave a state of the art panorama and discussed the perspectives about "Subduction...

Subduction Top to Bottom (Geophysical Monograph Series)

Subduction Top to Bottom (Geophysical Monograph Series)
by Gray E. Bebout (Editor), David W. Scholl (Editor), Stephen H. Kirby (Editor), John P. Platt (Editor)


Published by the American Geophysical Union as part of the Geophysical Monograph Series, Volume 96.

Perhaps no other plate tectonic setting has attracted as diverse multidisciplinary attention as convergent margins. This has in part been spurred by the extremely tangible hazards imposed by subduction, particularly in the form of earthquakes and tsunamis and arc volcanism. Concern regarding these hazards is heightened by the tendency of convergent margins to be heavily populated coastal regions. There has also been great interest in convergent margin settings for their potential (and demonstrated capability) of producing economically important oil and gas reservoirs and ore deposits. The cycling of materials (e.g., CO2 at convergent margins has been recognized as potentially...

Active tectonics of the Hellenic subduction zone (Springer Theses)

Active tectonics of the Hellenic subduction zone (Springer Theses)
by Beth Shaw (Author)


This thesis is remarkable for the wide range of the techniques and observations used and for its insights, which cross several disciplines. It begins by solving a famous puzzle of the ancient world, which is what was responsible for the tsunami that destroyed settlements in the eastern Mediterranean in 365 AD. By radiocarbon dating of preserved marine organisms, Shaw demonstrates that the whole of western Crete was lifted out of the sea by up to 10 meters in a massive earthquake at that time, which occured on a previously unknown fault. The author shows that the resulting tsunami would have the characteristics described by ancient writers, and uses modern GPS measurements and coastline geomorphology to show that the strain build-up near Crete requires such a tsunami-earthquake about every...

The Seismogenic Zone of Subduction Thrust Faults (MARGINS Theoretical and Experimental Earth Science Series)

The Seismogenic Zone of Subduction Thrust Faults (MARGINS Theoretical and Experimental Earth Science Series)
by Timothy H Dixon (Editor), Casey Moore (Editor)


Subduction zones, one of the three types of plate boundaries, return Earth's surface to its deep interior. Because subduction zones are gently inclined at shallow depths and depress Earth's temperature gradient, they have the largest seismogenic area of any plate boundary. Consequently, subduction zones generate Earth's largest earthquakes and most destructive tsunamis. As tragically demonstrated by the Sumatra earthquake and tsunami of December 2004, these events often impact densely populated coastal areas and cause large numbers of fatalities. While scientists have a general understanding of the seismogenic zone, many critical details remain obscure. This volume attempts to answer such fundamental concerns as why some interplate subduction earthquakes are relatively modest in rupture...

Full-Rip 9.0: The Next Big Earthquake in the Pacific Northwest

Full-Rip 9.0: The Next Big Earthquake in the Pacific Northwest
by Sasquatch Books


Scientists have identified Seattle, Portland, and Vancouver as the urban centers of what will be the biggest earthquake, also called a mega-quake, in the continental United States. A quake will happen--in fact it's actually overdue. The Cascadia subduction zone is 750 miles long, running along the Pacific coast from Northern California up to southern British Columbia. In this fascinating book, The Seattle Times science reporter Sandi Doughton introduces readers to the scientists who are dedicated to understanding the way the earth moves and describes what patterns can be identified and how prepared (or not) people are. With a 100% chance of a mega-quake hitting the Pacific Northwest, this fascinating book reports on the scientists who are trying to understand when, where, and just how big...

© 2014 BrightSurf.com