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


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.

Computer models solve geologic riddle millions of years in the making
An international team of scientists that included USC's Meghan Miller used computer modeling to reveal, for the first time, how giant swirls form during the collision of tectonic plates - with subduction zones stuttering and recovering after continental fragments slam into them.

Is there an ocean beneath our feet?
Scientists at the University of Liverpool have shown that deep sea fault zones could transport much larger amounts of water from the Earth's oceans to the upper mantle than previously thought.

Vancouver: Nearby Georgia basin may amplify ground shaking from next quake
Tall buildings, bridges and other long-period structures in Greater Vancouver may experience greater shaking from large (M 6.8 +) earthquakes than previously thought due to the amplification of surface waves passing through the Georgia basin.

Global map to predict giant earthquakes
A team of international researchers, led by Monash University's Associate Professor Wouter Schellart, have developed a new global map of subduction zones, illustrating which ones are predicted to be capable of generating giant earthquakes and which ones are not.

Runaway process drives intermediate-depth earthquakes, Stanford scientists find
Stanford scientists may have solved the mystery of what drives a type of earthquake that occurs deep within the Earth and accounts for one in four quakes worldwide.

Evidence found for granite on Mars
Researchers now have stronger evidence of granite on Mars and a new theory for how the granite - an igneous rock common on Earth -- could have formed there, according to a new study.

Methane seeps of the deep sea: A bacteria feast for lithodid crabs
The bottom of the deep sea is largely deserted. Oases occur for example at cold seeps where water transports dissolved elements from the seabed: Specialized microbes convert methane and sulfate from sea water to hydrogen sulfide releasing carbon dioxide.

Seismologists puzzle over largest deep earthquake ever recorded
A magnitude 8.3 earthquake that struck deep beneath the Sea of Okhotsk on May 24, 2013, has left seismologists struggling to explain how it happened. At a depth of about 609 kilometers (378 miles), the intense pressure on the fault should inhibit the kind of rupture that took place.

Subduction channel processes: New progress in plate tectonic theory
The plate tectonic theory has been primarily developed in three stages.
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 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...

The Art of Seduction

The Art of Seduction
by Robert Greene (Author)


Which sort of seducer could you be: *Siren? *Rake? *Cold Coquette? *Star? *Comedian? *Charismatic? or *Saint? This book will show you which. 'Charm, persuasion, the ability to create illusions: these are some of the many dazzling gifts of the Seducer, the compelling figure who is able to manipulate, mislead and give pleasure all at once. When raised to the level of art, seduction, an indirect and subtle form of power, has toppled empires, won elections and enslaved great minds. In this beautiful, sensually designed book, Greene unearths the two sides of seduction: the characters and the process. Discover who you, or your pursuer, most resembles. Learn, too, the pitfalls of the anti-Seducer. In part II, immerse yourself in the twenty-four manoeuvres and strategies of the seductive process,...

Turbidite Event History- Methods and Implications for Holocene Paleoseismicity of the Cascadia Subduction Zone

Turbidite Event History- Methods and Implications for Holocene Paleoseismicity of the Cascadia Subduction Zone
by U.S. Department of the Interior (Author)


Turbidite systems along the continental margin of Cascadia Basin from Vancouver Island, Canada, to Cape Mendocino, California, United States, have been investigated with swath bathymetry; newly collected and archive piston, gravity, kasten, and box cores; and accelerator mass spectrometry radiocarbon dates.

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 Sandi Doughton (Author)


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...

Deep-Sea Turbidities as Guides to Holocene Earthquake History at the Cascadia Subduction Zone-Alternative Views for a Seismic-Hazard Workshop

Deep-Sea Turbidities as Guides to Holocene Earthquake History at the Cascadia Subduction Zone-Alternative Views for a Seismic-Hazard Workshop
by U.S. Department of the Interior (Author)


This report reviews the geological basis for some recent estimates of earthquake hazards in the Cascadia region between southern British Columbia and northern California.

Subduction Zones Part II (Pageoph Topical Volumes)

Subduction Zones Part II (Pageoph Topical Volumes)
by Larry J. Ruff (Author), H. Kanamori (Author)


Reprint from Pure and Applied Geophysics (PAGEOPH), Volume 129 (1989), No. 1/2

Subduction: Insights from Physical Modeling (Modern Approaches in Geophysics)

Subduction: Insights from Physical Modeling (Modern Approaches in Geophysics)
by Alexander I. Shemenda (Author)


This book is devoted to the quantitative physical modeling of subduction and subduction-related processes. It presents a coherent description of the modeling method (including similarity criteria, and a novel applied experimental technique), results from model experiments, theoretical analysis of results on the basis of continuum mechanics, and their geodynamic interpretation. Subduction is modeled in general as well as applied to particular regions using both 2-D and 3-D approaches, with both slab-push and slab-pull driving forces. The modeling covers all stages from subduction initiation to `death', different regimes of subduction producing back arc extension and compression, blocking of subduction and jumps of subduction zone, arc-continent collision and continental...

  SUBDUCTION ZONE: An entry from Gale's World of Earth Science
by Gale (Publisher)


This digital document is an article from World of Earth Science, brought to you by Gale®, a part of Cengage Learning, a world leader in e-research and educational publishing for libraries, schools and businesses. The length of the article is 570 words. The article is delivered in HTML format and is available in your Amazon.com Digital Locker immediately after purchase. You can view it with any web browser. A comprehensive guide to the concepts, theories, discoveries, pioneers, and issues relating to topics in earth science. Its encyclopedic approach offers entries that are written in easy to understand language.

© 2014 BrightSurf.com