Life beyond Earth: No plate tectonics, no problem

Life beyond Earth: No plate tectonics, no problem

Scientists prepare to look in unexpected places for ‘exoplanet biosignatures’

HOUSTON — (March 28, 2018) — Scientists looking for life on distant planets are making plans to search non-Earth-like planets based on discoveries within our solar system that are challenging long-standing ideas about habitable zones, plate tectonics and more.

In a new paper published online this week, Rice University geophysicist Adrian Lenardic and more than a dozen co-authors outline a path for both finding potential life signs around other stars and determining how likely it is that those signs are caused by alien life. The paper, “Exoplanet Biosignatures: Future Directions,” is available online and due to be published in Astrobiology.

Lenardic, who specializes in studying planetary dynamics, also authored an associated paper, “Volcanic-Tectonic Modes and Planetary Life Potential,” that will be published as a chapter in the upcoming “Handbook of Exoplanets” from Springer Publishing.

An artist’s impression of Ross 128 b, a temperate, rocky planet about 11 light-years from Earth that could have the necessary conditions for maintaining liquid surface water. (Photo courtesy of European Southern Observatory/M. Kornmesser)

“It used to be the thought that life could only exist in a narrow zone near a planet’s star because you need to be there to maintain liquid water,” said Lenardic, professor of Earth, environmental and planetary sciences. “Then, we send Voyager out to a moon of Jupiter and, lo and behold, it shows strong indications of a subsurface ocean. That’s because there is another energy source that did not get its proper due — tidal forces from the intense gravitational pull of Jupiter.

“This has opened up the range over our own solar system in which life can exist, and I think a lot of the gist of the forthcoming papers is that much of what we’re seeing is expanding the zone and expanding our thinking about the conditions needed for life. So, as we look for life around other stars, we should also expand our search strategies or we might miss something.”

Astronomers have cataloged more than 3,700 planets around distant stars. The 21-foot diameter mirroron the James Webb Space Telescope, which is set to launch in 2019, will be able to examine the atmospheres of rocky planets around distant stars, and astronomers are already designing future missions and instruments that will look for specific atmospheric signatures of life.

“A goal was to frame the problem,” Lenardic said of the new biosignature paper, which sprang from an exoplanet workshop that brought together a range of scientists. “The workshop team wanted to come up with a means of assigning a likelihood of life based on a given set of observations of a distant planet.”

Adrian Lenardic (Photo by Jeff Fitlow/Rice University)

He said the search for exolife is a team sport that involves biologists, astronomers, planetary scientists and others who collaborate through groups such as NASA’s Nexus for Exoplanet System Science (NExSS) project and the European Space Agency’s International Summer School in Astrobiology.

Lenardic’s contribution is to examine how the internal energy of planets, and associated volcanic-tectonic activity, influence their climate and ability to sustain life.

“When I teach planetary science, one question I actually give students is, ‘What is life? Give me a definition.’ And it’s not easy,” Lenardic said. He noted that students and working scientists have put forward a range of answers.

“But if we can agree on one thing, it’s that life needs energy,” he said. “We’ve thought about the sun as an energy source for a long time, and we’ve come to appreciate a planet’s internal energy, which comes from decay of radioactive elements within its rocky interior. Jupiter’s moons have taught us to also appreciate tidal forcing, and we’re starting to find exoplanets that have orbits that allow for significant tidal forcing.”

Lenardic said plate tectonics, much like the narrow habitable zone, is another long-held criterion for planetary habitability that is being challenged by recent findings.

Plate tectonics is the large-scale process that governs the movements of Earth’s crust.

“It is a particular surface manifestation of a planet’s internal energy, but it is not the only possible mode of volcanic and tectonic activity on a planet,” Lenardic said.

On Earth, plate tectonics plays a role in modulating climate, but the idea that plate tectonics is crucial for life is challenged by increasingly sophisticated models of planetary climates. For example, in a January study in the Journal of Geophysical Research, Lenardic and colleagues showed how water could be maintained on worlds without plate tectonics. The chapter in the upcoming “Handbook of Exoplanets” further explores this idea by considering planetary life potential under a range of tectonic modes that differ from Earth’s.

“I’m an optimist,” Lenardic said. “We’re at the first point in our history as humans where we might actually have some observations from other planets that we can use to test any of these ideas about life beyond our own. It can be easy to be Earth-centric and assume that life requires a planet like our own. But what we are seeing within our solar system is causing us to question this. One of the things I have learned from the history of exploring our own solar system is to be prepared for surprise. As we move beyond our solar system, in our search for life, that lesson is driving us to adapt our search strategies.”

Co-authors of the Astrobiology paper include lead author Sara Walker, Evgenya Shkolnik and Harrison Smith of Arizona State University; William Bains of the MIT; Leroy Cronin of the University of Glasgow; Shiladitya DasSarma of the University of Maryland School of Medicine; Sebastian Danielache of the Tokyo Institute of Technology and Sophia University in Tokyo; Shawn Domagal-Goldman of NASA’s Goddard Space Flight Center and the University of Washington’s Virtual Planetary Laboratory; Betul Kacar of Harvard, the University of Montana and the University of Arizona; Nancy Kiang of NASA’s Goddard Institute for Space Studies; Christopher Reinhard of the University of California, Riverside and Georgia Tech; William Moore of Hampton University and the National Institute of Aerospace in Hampton, Va.; and Edward Schwieterman of the Blue Marble Space Institute of Science in Seattle, the University of Washington’s Virtual Planetary Laboratory, the University of California, Riverside and the Universities Space Research Association in Columbia, Md.

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Jeff Falk
713-348-6775
jfalk@rice.edu

Jade Boyd
713-348-6778
jadeboyd@rice.edu

Life beyond Earth: No plate tectonics, no problem
Scientists prepare to look in unexpected places for ‘exoplanet biosignatures’
HOUSTON — (March 28, 2018) — Scientists looking for life on distant planets are making plans to search non-Earth-like planets based on discoveries within our solar system that are challenging long-standing ideas about habitable zones, plate tectonics and more.

In a new paper published online this week, Rice University geophysicist Adrian Lenardic and more than a dozen co-authors outline a path for both finding potential life signs around other stars and determining how likely it is that those signs are caused by alien life. The paper, “Exoplanet Biosignatures: Future Directions,” is available online and due to be published in Astrobiology.

An artist’s impression of Ross 128 b, a temperate, rocky planet about 11 light-years from EarthLong Description
An artist’s impression of Ross 128 b, a temperate, rocky planet about 11 light-years from Earth that could have the necessary conditions for maintaining liquid surface water. (Photo courtesy of European Southern Observatory/M. Kornmesser)

Lenardic, who specializes in studying planetary dynamics, also authored an associated paper, “Volcanic-Tectonic Modes and Planetary Life Potential,” that will be published as a chapter in the upcoming “Handbook of Exoplanets” from Springer Publishing.

“It used to be the thought that life could only exist in a narrow zone near a planet’s star because you need to be there to maintain liquid water,” said Lenardic, professor of Earth, environmental and planetary sciences. “Then, we send Voyager out to a moon of Jupiter and, lo and behold, it shows strong indications of a subsurface ocean. That’s because there is another energy source that did not get its proper due — tidal forces from the intense gravitational pull of Jupiter.

“This has opened up the range over our own solar system in which life can exist, and I think a lot of the gist of the forthcoming papers is that much of what we’re seeing is expanding the zone and expanding our thinking about the conditions needed for life. So, as we look for life around other stars, we should also expand our search strategies or we might miss something.”

Astronomers have cataloged more than 3,700 planets around distant stars. The 21-foot diameter mirror on the James Webb Space Telescope, which is set to launch in 2019, will be able to examine the atmospheres of rocky planets around distant stars, and astronomers are already designing future missions and instruments that will look for specific atmospheric signatures of life.

“A goal was to frame the problem,” Lenardic said of the new biosignature paper, which sprang from an exoplanet workshop that brought together a range of scientists. “The workshop team wanted to come up with a means of assigning a likelihood of life based on a given set of observations of a distant planet.”

Adrian LenardicLong Description
Adrian Lenardic (Photo by Jeff Fitlow/Rice University)

He said the search for exolife is a team sport that involves biologists, astronomers, planetary scientists and others who collaborate through groups such as NASA’s Nexus for Exoplanet System Science (NExSS) project and the European Space Agency’s International Summer School in Astrobiology.

Lenardic’s contribution is to examine how the internal energy of planets, and associated volcanic-tectonic activity, influence their climate and ability to sustain life.

“When I teach planetary science, one question I actually give students is, ‘What is life? Give me a definition.’ And it’s not easy,” Lenardic said. He noted that students and working scientists have put forward a range of answers.

“But if we can agree on one thing, it’s that life needs energy,” he said. “We’ve thought about the sun as an energy source for a long time, and we’ve come to appreciate a planet’s internal energy, which comes from decay of radioactive elements within its rocky interior. Jupiter’s moons have taught us to also appreciate tidal forcing, and we’re starting to find exoplanets that have orbits that allow for significant tidal forcing.”

Lenardic said plate tectonics, much like the narrow habitable zone, is another long-held criterion for planetary habitability that is being challenged by recent findings.

Plate tectonics is the large-scale process that governs the movements of Earth’s crust.

“It is a particular surface manifestation of a planet’s internal energy, but it is not the only possible mode of volcanic and tectonic activity on a planet,” Lenardic said.

On Earth, plate tectonics plays a role in modulating climate, but the idea that plate tectonics is crucial for life is challenged by increasingly sophisticated models of planetary climates. For example, in a January study in the Journal of Geophysical Research, Lenardic and colleagues showed how water could be maintained on worlds without plate tectonics. The chapter in the upcoming “Handbook of Exoplanets” further explores this idea by considering planetary life potential under a range of tectonic modes that differ from Earth’s.

“I’m an optimist,” Lenardic said. “We’re at the first point in our history as humans where we might actually have some observations from other planets that we can use to test any of these ideas about life beyond our own. It can be easy to be Earth-centric and assume that life requires a planet like our own. But what we are seeing within our solar system is causing us to question this. One of the things I have learned from the history of exploring our own solar system is to be prepared for surprise. As we move beyond our solar system, in our search for life, that lesson is driving us to adapt our search strategies.”

Co-authors of the Astrobiology paper include lead author Sara Walker, Evgenya Shkolnik and Harrison Smith of Arizona State University; William Bains of the MIT; Leroy Cronin of the University of Glasgow; Shiladitya DasSarma of the University of Maryland School of Medicine; Sebastian Danielache of the Tokyo Institute of Technology and Sophia University in Tokyo; Shawn Domagal-Goldman of NASA’s Goddard Space Flight Center and the University of Washington’s Virtual Planetary Laboratory; Betul Kacar of Harvard, the University of Montana and the University of Arizona; Nancy Kiang of NASA’s Goddard Institute for Space Studies; Christopher Reinhard of the University of California, Riverside and Georgia Tech; William Moore of Hampton University and the National Institute of Aerospace in Hampton, Va.; and Edward Schwieterman of the Blue Marble Space Institute of Science in Seattle, the University of Washington’s Virtual Planetary Laboratory, the University of California, Riverside and the Universities Space Research Association in Columbia, Md.

Ash from dinosaur-era volcanoes linked with shale oil, gas

Ash from dinosaur-era volcanoes linked with shale oil, gas

Shale oil, gas deposits accompany ash layers from thousands of volcanic eruptions

Nutrient-rich ash from an enormous flare-up of volcanic eruptions toward the end of the dinosaurs’ reign kicked off a chain of events that led to the formation of shale gas and oil fields from Texas to Montana.

Cin-Ty Lee (photo by J. Fitlow)

That’s the conclusion of a new study by Rice University geologists that appears this week in Nature Publishing’s online journal Scientific Reports.

“One of the things about these shale deposits is they occur in certain periods in Earth’s history, and one of those is the Cretaceous time, which is around the time of the dinosaurs,” said study lead author Cin-Ty Lee, professor and chair of Rice’s Department of Earth, Environmental and Planetary Sciences. “This was about 90 million to 100 million years ago, which is about the same time as a massive flare-up of arc volcanoes along what is today the Pacific rim of the Western United States.”

Advances in horizontal drilling and hydraulic fracturing over the past 20 years led to a U.S. energy boom in “unconventionals,” a category that includes the shale gas and “tight” oil found in shale fields like the Cretaceous Eagle Ford and Mowry and older ones like the Barnett and Bakken.

An enormous volcanic flare-up at the end of the dinosaurs’ reign kicked off a chain of events that led to the formation of the U.S. shale oil and gas fields from Texas to Montana. Rice University geologists said older shale gas fields, like the Marcellus in Pennsylvania and Ohio, may have formed from similar volcanic flare-ups hundreds of millions of years earlier. (Photo courtesy of Wikimedia Commons)

“These types of natural gas and oil are in tiny, tiny pores that range from a few millionths of a meter in diameter to a few thousandths of a meter,” Lee said. “The deposits are in narrow bands that can only be accessed with horizontal drilling, and the oil and gas are locked in these little pockets and are only available with techniques like hydraulic fracturing.”

Lee said that there have always been hints of a connection between ancient volcanic eruptions and unconventional shale hydrocarbons. During field trips out to West Texas, he and Rice students noticed hundreds of ash layers in exposed rock that dated to the Cretaceous period when much of western North America lay beneath a shallow ocean.

One of these trips happened in 2014 while Lee and Rice colleagues also were studying how a flare-up of Cretaceous-era arc volcanoesalong the U.S. Pacific rim had impacted Earth’s climate through enhanced volcanic production of carbon dioxide.

“We had seen ash layers before, but at this site we could see there were a lot of them, and that got us thinking,” Lee said. Lee, graduate student Hehe Jiang and Rice undergraduates Elli Ronay, Jackson Stiles and Matthew Neal decided to investigate the ash beds in collaboration with Daniel Minisini, a colleague at Shell Oil who had been doing extensive work on quantifying the exact number of ash beds.

The eruption of Alaska’s Pavlof Volcano as seen from the International Space Station May 18, 2013. The volcano’s ash cloud rose to 20,000 feet and extended over hundreds of miles of the northern Pacific Ocean. (Photo courtesy of NASA/ISS Crew Earth Observations experiment and Image Science and Analysis Laboratory, Johnson Space Center)

“It’s almost continuous,” Lee said. “There’s an ash layer at least every 10,000 years.”

Lee said the team determined that ash had come from hundreds of eruptions that spanned some 10 million years. The layers had been transported several hundred miles east of their volcanic source in California. The ash was deposited on the seafloor after being blown through plumes that rose miles into the atmosphere and drifted over the ocean. Lee and students analyzed samples of the ash beds in the geochemical facilities at Rice.

“Their chemical composition didn’t look anything like it would have when they left the volcano,” he said. “Most of the original phosphorus, iron and silica were missing.”

That brought to mind the oceanic “dead zones” that often form today near the mouths of rivers. Overfertilization of farms pumps large volumes of phosphorus down these rivers. When that hits the ocean, phytoplankton gobble up the nutrients and multiply so quickly they draw all the available oxygen from the water, leaving a “dead” region void of fish and other organisms.

Lee suspected the Cretaceous ash plumes might have caused a similar effect. To nail down whether the ash could have supplied enough nutrients, Lee and his team used trace elements like zirconium and titanium to match ash layers to their volcanic sources. By comparing rock samples from those sources with the depleted ash, the team was able to calculate how much phosphorus, iron and silica were missing.

Oxygen-depleted “dead zones” often form in the northern Gulf of Mexico due to nutrient-rich runoff from the Mississippi and Atchafalaya rivers, which are seen here as tan and greenish-brown plumes visible from the International Space Station in 2012. Nutrient-rich volcanic ash may have fed similar dead zones that produced shale oil and gas fields from Texas to Montana. (Photo courtesy of NASA/GSFC/Aqua MODIS)

“Normally, you don’t get any deposition of organic matter at the bottom of the water column because other living things will eat it before it sinks to the bottom,” Lee said. “We found the amount of phosphorus entering the ocean from this volcanic ash was about 10 times more than all the phosphorus entering all the world’s oceans today. That would have been enough to feed an oxygen-depleted dead zone where carbon could be exported all the way down to the sediment.”

The combination of the ashfall and oceanic dead zone concentrated enough carbon to form hydrocarbons.

“To generate a hydrocarbon deposit of economic value, you have to concentrate it,” Lee said. “In this case, it got concentrated because the ashes drove that biological productivity, and that’s where the organic carbon got funneled in.”

Lee said shale gas and tight oil deposits are not found in the ash layers but appear to be associated with them. Because the layers are so thin, they don’t show up on seismic scans that energy companies use to look for unconventionals. The discovery that hundreds of closely spaced ash layers could be a tell-tale sign of unconventionals might allow industry geologists to look for bulk properties of ash layers that would show up on scans, Lee said.

“There also are implications for the nature of marine environments,” he said. “Today, phosphorus is also a limiting nutrient for the oceans, but the input of the phosphorus and iron into the ocean from these volcanoes has major paleoenvironmental and ecological consequences.”

While the published study looked specifically at the Cretaceous and North America, Lee said arc volcano flare-ups at other times and locations on Earth may also be responsible for other hydrocarbon-rich shale deposits.

“I suspect they could,” he said. “The Vaca Muerta field in Argentina is the same age and was behind the same arc as what we were studying. The rock record gets more incomplete as you go further back in time, but in terms of other U.S. shales, the Marcellus in Pennsylvania was laid down more than 400 million years ago in the Ordovician, and it’s also associated with ashes.”

The research was funded by the National Science Foundation, the Guggenheim Foundation and the Geological Society of America.

After the fire, charcoal goes against the grain, with the flow

After the fire, charcoal goes against the grain, with the flow

Rice U. wildfire study: Soil charcoal became more concentrated over time

When a forest fire decimated more than 3,000 acres of Rice University-owned timberland in 2011, biogeochemist Carrie Masiello saw a silver lining in the blackened trees.

The Tri-County wildfire in September 2011 destroyed more than 18,000 acres of forest, including a Rice University-owned tract in Waller County, Texas. (Photo courtesy of C. Masiello/Rice University)

Masiello is an expert on how carbon behaves in soil, and she noticed a vexing problem in both the scientific literature and findings from her lab: Charcoal is abundant in soil, particularly in fertile regions like Europe’s breadbasket and America’s Corn Belt, but while it’s clear that most soil charcoal came from wildfires, it wasn’t at all clear why it stayed there so long or how it got into the soil after a fire.

In a newly published study in the Journal of Geophysical Research, Masiello and colleagues, including current and former graduate students Lacey Pyle and Kate Magee, analyzed soil samples collected after the fire and found that charcoal behaved very differently from other forms of soil carbon as the land rebounded from the fire.

“We looked at all forms of carbon in the soil, both immediately after the fire and over a two-year period, and we found that it became more evenly distributed over time, which is a sign that the land was returning to its baseline state,” Masiello said. “Charcoal behaves exactly the opposite. It’s distribution became more patchy over time, and we think that’s because it’s buoyant and gets moved by water and concentrated in low places on the landscape.”

Carrie Masiello (left) and Lacey Pyle. (Photo by Jeff Fitlow/Rice University)

Masiello said it was not a surprise that charcoal was buoyant. In fact, the research team had specifically chosen flat research sites because previous studies had shown that soil carbon tended to migrate downhill over time. The surprise was the extent to which charcoal from the fire had become concentrated, even in the absence of notable topographic relief.

“It was redistributed on the landscape pretty effectively,” said Pyle ’09, the lead author of the study. “Rather than staying where it was initially deposited, it had a tendency to move horizontally across the landscape. The total contents of charcoal in our study sites didn’t change that drastically over the time period, but where we were finding it changed quite a bit.”

Charcoal’s benefits as a soil amendment are fourfold: It reduces atmospheric carbon dioxide and pollution, improves crop productivity, allows agriculture in areas with marginal soils and makes soil more resilient to both drought and flooding.

Rice University graduate student Lacey Pyle uses a magnifying glass and tweezers to find charcoal in dozens of soil samples. (Photo by Jeff Fitlow/Rice University)

In 2008, Masiello and study co-author William Hockaday, then at Rice and presently at Baylor University, began seriously studying soil charcoal after winning a $10,000 prize in the city of Houston’s “Recycle Ike” contest in the wake of Hurricane Ike. The storm left 5.6 million cubic yards of fallen trees, broken branches and dead greenery in Houston, and Rice’s team took first place in the contest with their plan to convert the wood into biomass charcoal, or “biochar,” for use as a CO2-trapping soil amendment.

In subsequent studies, Masiello’s lab has explored biochar’s productionmicrobial impactshydrological characteristics and pollution-reducing effects.

“More carbon in soil is good, and as we think about ways to stabilize and increase soil carbon inventory, charcoal is an obvious option,” Masiello said.

To get the most benefit from biochar, Masiello said, scientists and land managers need to better understand the fate and transport of soil charcoal, and studying naturally occurring soil charcoal is a great way to gain that understanding.

When added to soil, charcoal can reduce nutrient pollution, lower atmospheric carbon dioxide, improve crop productivity and make soil more resilient to both drought and flooding. (Image courtesy of Ghasideh Pourhashem)

“We know that lots of carbon in soil is old,” she said, adding that the ages of soil charcoal measured with radiocarbon dating “suggest that it’s hard to decompose. But when we bring it into the lab, it turns out it’s not that hard to decompose.”

The findings from the wildfire study offer a new clue as to how naturally occurring charcoal can remain stable for long periods of time, Masiello said.

“It’s possible that the mobility of charcoal on the landscape and it’s tendency to become concentrated in low-lying spots could make it more likely the charcoal from wildfires becomes buried and incorporated deep in soils and that these deposits act as a kind of charcoal reservoir that releases charcoal into the soil over long time spans.”

The research was funded by Rice University and Chevron. Additional co-authors include postdoctoral research associate Morgan Gallagher.

Heavy nitrogen molecules reveal planetary-scale tug-of-war

Rice, UCLA, Michigan State, UNM find unusual enrichment in 15N15N molecules

Nature whispers its stories in a faint molecular language, and Rice University scientist Laurence Yeung and colleagues can finally tell one of those stories this week, thanks to a one-of-a-kind instrument that allowed them to hear what the atmosphere is saying with rare nitrogen molecules.

Yeung and colleagues at Rice, UCLA, Michigan State University and the University of New Mexico counted rare molecules in the atmosphere that contain only heavy isotopes of nitrogen and discovered a planetary-scale tug-of-war between life, the deep Earth and the upper atmosphere that is expressed in atmospheric nitrogen.

The research was published online this week in the journal Science Advances.

“We didn’t believe it at first,” said Yeung, the lead author of the study and an assistant professor of Earth, environmental and planetary sciences at Rice. “We spent about a year just convincing ourselves that the measurements were accurate.”

The story revolves around nitrogen, a key element of life that makes up more than three-quarters of Earth’s atmosphere. Compared with other key elements of life like oxygen, hydrogen and carbon, nitrogen is very stable. Two atoms of it form N2 molecules that are estimated to hang around in the atmosphere for about 10 million years before being broken apart and reformed. And the vast majority of nitrogen has an atomic mass of 14. Only about 0.4 percent are nitrogen-15, an isotope that contains one extra neutron. Because nitrogen-15 is already rare, N2 molecules that contain two nitrogen-15s — which chemists refer to as 15N15N — are the rarest of all N2 molecules.

The new study shows that 15N15N is 20 times more enriched in Earth’s atmosphere than can be accounted for by processes happening near Earth’s surface.

Rice Assistant Professor Laurence Yeung. Photo by Jeff Fitlow

 

“We think the 15N15N enrichment fundamentally comes from chemistry in the upper atmosphere, at altitudes close to the orbit of the International Space Station,” Yeung said. “The tug-of-war comes from life pulling in the other direction, and we can see chemical evidence of that.”

Co-author Edward Young, professor of Earth, planetary and space sciences at UCLA, said, “The enrichment of 15N15N in Earth’s atmosphere reflects a balance between the nitrogen chemistry that occurs in the atmosphere, at the surface due to life and within the planet itself. It’s a signature unique to Earth, but it also gives us a clue about what signatures of other planets might look like, especially if they are capable of supporting life as we know it.”

The chemical processes that produce molecules like N2 can change the odds that “isotope clumps” like 15N15N will be formed. In previous work, Yeung, Young and colleagues used isotope clumps in oxygen to identify tell-tale signatures of photosynthesis in plants and ozone chemistry in the atmosphere. The nitrogen study began four years ago when Yeung, then a postdoctoral researcher at UCLA, learned about a first-of-its-kind mass spectrometer that was being installed in Young’s lab.

The amount of nitrogen molecules in Earth’s atmosphere that contain only heavy isotopes result from a balance between nitrogen chemistry that occurs in the atmosphere, at the surface due to life and within the planet itself. (Photo courtesy of ISS Expedition 7 Crew, EOL, NASA)

“At that time, no one had a way to reliably quantify 15N15N,” said Yeung, who joined Rice’s faculty in 2015. “It has an atomic mass of 30, the same as nitric oxide. The signal from nitric oxide usually overwhelms the signal from 15N15N in mass spectrometers.”

The difference in mass between nitric oxide and 15N15N is about two one-thousandths the mass of a neutron. When Yeung learned that the new machine in Young’s lab could discern this slight difference, he applied for grant funding from the National Science Foundation (NSF) to explore exactly how much 15N15N was in Earth’s atmosphere.

“Biological processes are hundreds to a thousand times faster at cycling nitrogen through the atmosphere than are geologic processes,” Yeung said. “If it’s all business as usual, one would expect that the atmosphere would reflect these biological cycles.”

To find out if this was the case, co-authors Joshua Haslun and Nathaniel Ostrom at Michigan State University conducted experiments on N2-consuming and N2-producing bacteria to determine their 15N15N signatures.

These experiments suggested that one should see a bit more 15N15N in air than random pairings of nitrogen-14 and nitrogen-15 would produce — an enrichment of about 1 part per 1,000, Yeung said.

Researchers from Rice University and UCLA simulated high-energy chemistry in the upper atmosphere to reproduce enriched levels of 15N15N, molecules that contain only heavy isotopes of nitrogen. (Photo by Laurence Yeung/Rice University)

“There was a bit of enrichment in the biological experiments, but not nearly enough to account for what we’d found in the atmosphere,” Yeung said. “In fact, it meant that the process causing the atmospheric 15N15N enrichment has to fight against this biological signature. They are locked in a tug-of-war.”

The team eventually found that zapping mixtures of air with electricity, which simulates the chemistry of the upper atmosphere, could produce enriched levels of 15N15N like they measured in air samples. Mixtures of pure nitrogen gas produced very little enrichment, but mixtures approximating the mix of gases in Earth’s atmosphere could produce a signal even higher than what was observed in air.

“So far we’ve tested natural air samples from ground level and from altitudes of 32 kilometers, as well as dissolved air from shallow ocean water samples,” he said. “We’ve found the same enrichment in all of them. We can see the tug-of-war everywhere.”

Co-authors include Huanting Hu of Rice, Shuning Li, formerly of Rice and UCLA and now with Peking University in Beijing, Issaku Kohl and Edwin Schauble of UCLA and Tobias Fischer of the University of New Mexico.

The research was supported by the NSF, the Deep Carbon Observatory and the Department of Energy’s Great Lakes Bioenergy Research Center.

Reefs near Texas endured punctuated bursts of sea-level rise before drowning

Fossil coral reefs show sea level rose in bursts during last warming
JADE BOYD – OCTOBER 19, 2017
POSTED IN: CURRENT NEWS, FEATURED STORIES

 

https://youtu.be/jv9VA797Veo
Reefs near Texas endured punctuated bursts of sea-level rise before drowning

Scientists from Rice University and Texas A&M University-Corpus Christi’s Harte Research Institute for Gulf of Mexico Studies have discovered that Earth’s sea level did not rise steadily but rather in sharp, punctuated bursts when the planet’s glaciers melted during the period of global warming at the close of the last ice age. The researchers found fossil evidence in drowned reefs offshore Texas that showed sea level rose in several bursts ranging in length from a few decades to one century.

The findings appear today in Nature Communications.

“What these fossil reefs show is that the last time Earth warmed like it is today, sea level did not rise steadily,” said Rice marine geologist André Droxler, a study co-author. “Instead, sea level rose quite fast, paused, and then shot up again in another burst and so on.

“This has profound implications for the future study of sea-level rise,” he said.


Rice University researchers (from left to right) Pankaj Khanna, André Droxler and Jeffrey Nittrouer. (Photo by Jeff Fitlow/Rice University)

Because scientists did not previously have specific evidence of punctuated decade-scale sea-level rise, they had little choice but to present the risks of sea-level rise in a linear, per-year format, Droxler said. For example, the International Panel on Climate Change, the authoritative scientific source about the impacts of human-induced climate change, “had to simply take the projected rise for a century, divide by 100 and say, ‘We expect sea level to rise this much per year,’” he said.

“Our results offer evidence that sea level may not rise in an orderly, linear fashion,” said Rice coastal geologist and study co-author Jeff Nittrouer.

Given that more than half a billion people live within a few meters of modern sea level, he said punctuated sea-level rise poses a particular risk to those communities that are not prepared for future inundation.


André Droxler (seated) and Pankaj Khanna aboard the research vessel Falkor in 2012. (Photo by Mark Schrope/Schmidt Ocean Institute)

“We have observed sea level rise steadily in contemporary time,” Nittrouer said. “However, our findings show that sea-level rise could be considerably faster than anything yet observed, and because of this situation, coastal communities need to be prepared for potential inundation.”

The study’s evidence came from a 2012 cruise by the Schmidt Ocean Institute‘s research vessel Falkor. During the cruise, Droxler, study lead author and Rice graduate student Pankaj Khanna and Harte Research Institute colleagues John Tunnell Jr. and Thomas Shirley used the Falkor’s multibeam echo sounder to map 10 fossil reef sites offshore Texas. The echo sounder is a state-of-the-art sonar that produces high-resolution 3-D images of the seafloor.


A high-resolution 3-D map of Southern Bank off the South Texas coast clearly reveals terraces, which are a characteristic coral reef response to rising sea level. (Image courtesy of P. Khanna/Rice University)

The fossil reefs lie 30-50 miles offshore Corpus Christi beneath about 195 feet of water. Sunlight does not reach them at that depth, but because corals live in symbiosis with algae, they need sunlight to live and only grow at or very near sea level. Based on previous studies of the Texas coastline during the last ice age as well as the dates of fossils samples collected from the reefs in previous expeditions, the Rice team surmised that the reefs began forming about 19,000 years ago when melting ice caps and glaciers were causing sea level to rise across the globe.

“The coral reefs’ evolution and demise have been preserved,” Khanna said. “Their history is written in their morphology — the shapes and forms in which they grew. And the high-resolution 3-D imaging system on the R/V Falkor allowed us to observe those forms in extraordinary detail for the first time.”

All the sites in the study had reefs with terraces. Khanna said the stair-like terraces are typical of coral reef structures and are signatures of rising seas. For example, as a reef is growing at the ocean’s surface, it can build up only so fast. If sea level rises too fast, it will drown the reef in place, but if the rate is slightly slower, the reef can adopt a strategy called backstepping. When a reef backsteps, the ocean-facing side of the reef breaks up incoming waves just enough to allow the reef to build up a vertical step.


A 3-D representation of Dream Bank, a long-dead reef offshore South Texas. The vertical scale of the image has been increased to clearly illustrate the terrace structures that form due to rising sea levels via a process known as backstepping. (Image courtesy of P. Khanna/Rice University)

“In our case, each of these steps reveals how the reef adapted to a sudden, punctuated burst of sea-level rise,” Khanna said. “The terraces behind each step are the parts of the reef that grew and filled in during the pauses between bursts.”

Some sites had as many as six terraces. The researchers said it’s important to note that even though the sites in the study are as much as 75 miles apart, the depth of the terraces lined up at each site. Droxler and Nittrouer credited the find to Khanna’s determination. Analysis of the data from the mapping mission took more than a year, and the time needed to respond to questions that arose during the publication’s peer-review process was even longer.

“That’s the way science works,” Droxler said. “This is the first evidence ever offered for sea-level rise on a time scale ranging from decades to one century, and our colleagues expected ironclad evidence to back that claim.”


Rice researchers (from left) Caleb McBride, André Droxler and Pankaj Khanna aboard the research vessel Falkor in 2012. (Photo courtesy of A. Droxler/Rice University)

Nittrouer said the scenario of punctuated sea-level rise is one that many scientists had previously suspected.

“Scientists have talked about the possibility that continental ice could recede rapidly,” he said. “The idea is that sudden changes could arise when threshold conditions are met — for example, a tipping point arises whereby a large amount of ice is released suddenly into global oceans. When melted, this adds water volume and raises global sea level.”

Khanna said it’s likely that additional fossil evidence of punctuated sea-level rise will be found in the rock record at sites around the globe.

“Based on what we’ve found, it is possible that sea-level rise over decadal time scales will be a key storyline in future climate predictions,” he said.

The research was supported by Rice University, the Harte Research Institute at Texas A&M University-Corpus Christi and the Schmidt Ocean Institute.

 

Rice’s Clint Miller ready to study first cores from Gulf of Corinth rift

Rice scientist ready to study first cores from active continental rift

Rice’s Clint Miller ready to study first cores from Gulf of Corinth rift

By Linda Welzenbach
Special to Rice News

Rice geochemist Clint Miller is part of an international team of scientists that is collecting the first sediment samples ever drilled from Greece’s Gulf of Corinth, an active continental rift where Earth’s crust expands and thins.

“The Gulf is somewhat unique because it is an active rift that has oscillated over the last few million years between lake-like conditions and true marine conditions,” said Miller, a postdoctoral research associate in the Department of Earth, Environmental and Planetary Sciences. “Hopefully, we will be able to see this really clearly in the chemistry of the sediments we collect.”

Clint Miller

Miller said scientists are especially interested in such continental rift zones because they are geologically active and often at risk for earthquakes and volcanic eruptions. “They also present a unique opportunity to observe plate tectonics in action,” he said.

Miller and colleagues sailed on the British Geologic Survey drilling vessel Fugro Synergyto collect samples from the Corinth rift in the Mediterranean Sea. The expedition is sponsored by the the International Ocean Discovery Program (IODP) and European Consortium for Ocean Research Drilling.

Gulf of Corinth

Having formed its modern expression over the past 5 million years, the Corinth rift is young for an active continental rift zone. It’s situated across a shallow marine basin about 30 miles west of Athens and has a closed drainage system that Miller said makes it ideal for studying early rift development and the way land forms when it is subject to competing forces from tectonics and climate.Miller and colleagues sailed on the British Geologic Survey drilling vessel Fugro Synergyto collect samples from the Corinth rift in the Mediterranean Sea. The expedition is sponsored by the the International Ocean Discovery Program (IODP) and European Consortium for Ocean Research Drilling.

The rift is spreading at a rate of about 10-15 millimeters per year, and rivers that drain into the Gulf carry sediments that partially fill the rift zone as it spreads. Miller said IOPD Expedition 381 differs from most scientific drilling missions because it aims to drill only three holes and to do so in a way that maximizes what scientists can learn.

He hopes drilling in carefully selected locations will enable them to collect sediment samples from across tens of thousands of years.

“From a paleoceanographic perspective, that is the best scenario for capturing reliable climate cycle information from seafloor sediments,” he said.

One of Miller’s tasks on ship will be to analyze the chemistry of water that is trapped in the pores of sediments that have been buried in the rift for up to 2 million years. Because the water was trapped inside the sediments as they were buried, it can help tell the story of the Gulf’s past.

“Pore water and ocean sediment tell how the climate and biosphere have changed over time,” he said. “From the types of organic carbon and related compounds that are present, we can get the rates of photosynthesis as well as the sediment and water chemistry of the past. That will tell us how life responded to the rift and to changing sea level.”After the cruise, Miller will conduct more in-depth experiments at IODP’s core storage facility in Bremen, Germany.

Ultimately, Miller hopes to help address the hypothesis that environmental fluctuations preserved in the Corinth rift are related to 100,000-year climate cycles.

“We would like to know how the rift environment affects the deposition of carbon during glacial and interglacial time periods,” he said. “This will help us better understand how climate affects Earth’s biosphere, which is increasingly important due to human-induced climate change.”

To track the expedition’s progress or learn more, visit the IODP Expedition 381 blog.

–Linda Welzenbach is a science writer in the Department of Earth, Environmental and Planetary Sciences at Rice.

Rice’s Laurence Yeung named 2017 Packard Fellow

Rice’s Laurence Yeung named 2017 Packard Fellow

Geochemist wins prestigious grant for innovative research into ‘clumped’ isotopes

HOUSTON — (Oct. 16, 2017) — Rice University’s Laurence Yeung has made a career of searching for some of Earth’s rarest molecules and the stories they tell about the planet’s past, present and future. To aid his search, the David and Lucile Packard Foundation has awarded Yeung a 2017 Packard Fellowship for Science and Engineering.

Packard Fellowships, which include a largely unrestricted five-year research grant of $875,000, are among the most prestigious early career awards for U.S. scientists and engineers. Only 18 are awarded each year.

“My first response was excitement: ‘Oh my God. I cannot believe this is happening,’ and then I looked at everyone who’d come before and won one of these, and I thought, ‘Really? How can I be one of these people?’” said Yeung, assistant professor of Earth, environmental and planetary sciences. “The way I think about it is, ‘Congratulations. Now, earn it.’”

Laurence Yeung

Yeung joined Rice in 2015. His research is a mix of physical chemistry, photochemical experimentation, quantum-mechanical theory, atmospheric modeling and more, all aimed at understanding how the atmosphere broadcasts the state of the Earth system in its chemical composition.

“People sometimes call the atmosphere the ‘great communicator’ because it’s the first to respond to any perturbation in Earth systems,” Yeung said. “Altering anything from volcanic emissions to biological productivity can result in changes in the atmosphere’s makeup and its chemistry.”

He said there are many processes scientists still don’t understand about the atmosphere’s basic workings. For example, they cannot confidently predict how much the atmosphere will warm or cool if it has different amounts of greenhouse gases. They also don’t know how the composition of the atmosphere changes as the biosphere responds to global change.

“Understanding these processes and others could help us better understand climate dynamics, the evolution of Earth’s surface and even how to search for life on other planets,” Yeung said.

His core approach typically revolves around counting exact numbers of extraordinarily rare molecules that contain two or more rare isotopes, atoms of the same element that differ only in their mass. Fundamental processes — like photosynthesis in plants or ozone chemistry in the atmosphere — change the odds that “clumped” isotopes will be created. For each process, the odds change in a characteristic way, which means clumped isotopes can serve as calling cards for specific processes.

However, sifting through millions of molecules to find a handful of these ultrarare clumped isotopes is not uncommon. “The measurements we do are incredibly hard,” Yeung said. “It takes big, heavy instruments to measure a small number of samples extremely carefully.”

He said the Packard Fellowship will allow him to take research risks he couldn’t otherwise afford. Some of these risks involve finding new archives for ancient atmospheric properties, while others entail discovering new ways to detect the imprints of life in a variety of environments.

“Basically, every one of these ideas is risky,” he said. “In some cases, you’re not sure about the math or the model that you’ve put together. There could also be questions about your samples. And even if you get all of that right, your instruments might not be good enough to resolve the detail that’s necessary.”

One project he’s considering is attempting to create a compact device that makes isotopic measurements far more accessible.

“It’s unlikely that this device will be able to make measurements with the same precision that we do in the lab today, but if the precision were good enough, and we could go places — a boat, a mountaintop, a drone — and collect tenfold or hundredfold more data, it would be transformative.

“At the end of five years, I’d like to see that some of the risks paid off and some didn’t,” he said. “If they all pay off, then you’re not taking enough chances and pushing to stay right there at the edge of what’s possible.”

Other Rice faculty who have been named Packard Fellows include Cin-Ty Lee and Rajdeep Dasgupta, also of the Department of Earth, Environmental and Planetary Sciences, and Doug Natelson and Tom Killian, both of the Department of Physics and Astronomy.

Since the Packard Fellows program was begun in 1988, the Packard Foundation has awarded $394 million to support 577 scientists and engineers from 54 top universities. Packard Fellows have gone on to receive awards and honors that include the Nobel Prize in Physics, the Fields Medal, the Alan T. Waterman Award, MacArthur Fellowships and election to the National Academies.

 

A high-resolution IMAGE is available for download at:

http://news.rice.edu/files/2017/10/1016_PACKARD-yeung136-lg-1i08jz2.jpg
CAPTION: Laurence Yeung (Photo by Jeff Fitlow/Rice University)

Related stories from Rice:

Earth scientist Laurence Yeung wins Clarke Award — Feb. 29, 2016
http://news.rice.edu/2016/02/29/earth-scientist-laurence-yeung-wins-clarke-award/

Oxygen atmosphere recipe = tectonics + continents + life — May 16, 2016
http://news.rice.edu/2016/05/16/oxygen-atmosphere-recipe-tectonics-continents-life/

Study: Photosynthesis has unique isotopic signature — April 23, 2015
http://news.rice.edu/2015/04/23/study-photosynthesis-has-unique-isotopic-signature/

Xiaodong Gao aiming for the six World Marathon Majors

Research scientist aiming for the six World Marathon Majors
B.J. ALMOND – OCTOBER 6, 2017
POSTED IN: RICE CURRENT NEWS

When research scientist Xiaodong Gao crossed the finish line at the Berlin Marathon Sept. 24, he reached the halfway mark to his goal of running six of the world’s largest and most-renowned marathons.

Having completed the Chicago Marathon in 2016 and the Boston Marathon this past April, the 40-year-old native of China’s Jiangsu province still needs to run the New York City, Tokyo and London marathons to earn the highly coveted medal awarded to finishers of the six World Marathon Majors.

Xiaodong Gao holds his finisher’s medal from the Berlin Marathon while displaying medals from Houston, Chicago and Boston marathons and the Texas Independence Relay.

That goal wasn’t even remotely on Gao’s radar four years ago when he started running. In October 2013 Gao went for a health checkup and discovered that his cholesterol was “off the charts.”

“I needed to do something to change that,” said Gao, whose weight of 220 pounds was due more to his girth than his height of 6 feet. He began running in his Clear Lake neighborhood early in the morning before going to his lab at Rice, where he studies the chemical signals of biochar.

A year later he was running 50 to 60 miles a week to train for his first 26.2-mile race – the 2015 Houston Marathon, which he finished in 3:25:01. He shaved more than 15 minutes off that time when he ran Houston again in 2016 in 3:09:55 – a time fast enough to qualify for the Boston Marathon.

“Once I qualified for Boston, I thought, ‘Why not try to do all six world marathon majors?’” Gao said. “It would give me the chance to experience different cultures, traditions and food, and you get that nice medal after you finish all six.”

Gao ran Boston in 3:27 and fondly remembers the cheering crowds that lined the race route “like crazy.” He was unable to improve on that time in the Berlin Marathon, which he ran in 3:35, due to rain, heat and 100 percent humidity the day of the race and Houston’s summer temperatures, which are not ideal for marathon training. “But the really excited crowds at the finish line made me very happy,” Gao said. He celebrated by drinking “a lot of beer” in Germany, and he and his wife turned the trip into a mini vacation by visiting several museums in Berlin.

As Gao was upping his mileage to train for marathons, he was having difficulty finding people to run with. So he used social media to co-found the Houston Long Running Club, which now has more than 400 members throughout the Houston area. “Training with a friend makes it easier and more fun,” he said. “We offer our experience to help other people who are learning to run, and we celebrate after a race by drinking and eating together.” One of his favorite post-race foods is mala Sichuan, a spicy and hot Chinese cuisine.

In addition to running marathons, members of the Houston Long Running Club have formed teams to run the Texas Independence Relay, which starts in Gonzales, where the Texas Revolution began, and finishes more than 200 miles away at the San Jacinto Monument, where Texas won its independence, near the Houston Ship Channel. Gao has competed in the two-day relay twice and will be captain of his 12-member team in the 2018 relay.

Gao hopes that 2018 will also be the year his application gets selected in the random drawings for entry in the New York City Marathon. And he plans to run the Houston Marathon again in January with hopes of setting a personal record. “I’d like to break three hours,” he said. “If everything goes right, it will be like winning the lottery.”

Due to the expense and time commitment to travel to London and Tokyo, Gao doesn’t expect to run marathons there until 2019, provided that his name gets picked in the lottery for each race.

Meanwhile, he expects that his total running mileage, which he records daily, will pass 10,000 miles by the end of this year.

“Running is a great way to relieve the pressure from daily life even though it’s difficult to find time to train when you have a full-time job and a family to take care of,” Gao said. “And I want to set a good example for my two kids. You set a goal and work hard for it. If you achieve your goal, that’s great. If not, accept it and work harder next time.”

“Xiaodong is an excellent scientist, and we’re lucky to have him in the department,” said Carrie Masiello, professor of Earth, environmental and planetary sciences, whose research group includes Gao. “He’s a strong analytical chemist and he’s also a thoughtful mentor of students in the lab, transferring his knowledge to others. He’s also especially good at seeing tasks through to completion. He is not deterred by analytical or intellectual challenges, and he likes to close on projects, making sure that his teams’ projects get all the way to publication. I think this drive to finish tasks thoroughly and completely is consistent between his research and marathoning.”

The desire for better health that motivated Gao to start running has paid off: He now weighs 160 pounds. But that presented a problem of its own. When he was visiting his parents in China, he tried to exchange currency at a bank there. The clerk did not think Gao was the person pictured on his Chinese ID because the photo had been taken prior to his dramatic weight loss. “It’s not you,” Gao remembered the clerk saying. “I had to show them some alternate forms of ID to convince them who I am.”

Hot spot at Hawaii? Not so fast

– AUGUST 18, 2017

Hot spot at Hawaii? Not so fast

Rice University scientists’ model shows global mantle plumes don’t move as quickly as thought

HOUSTON – (Aug. 18, 2017) – Through analysis of volcanic tracks, Rice University geophysicists have concluded that hot spots like those that formed the Hawaiian Islands aren’t moving as fast as recently thought.

Hot spots are areas where magma pushes up from deep Earth to form volcanoes. New results from geophysicist Richard Gordon and his team confirm that groups of hot spots around the globe can be used to determine how fast tectonic plates move.

Rice University geophysicists have developed a method that uses the average motion of hot-spot groups by plate to determine that the spots aren't moving as fast as geologists thought. For example, the Juan Fernandez Chain (outlined by the white rectangle) on the Nazca Plate west of Chile was formed by a hot spot now at the western end of the chain as the Nazca moved east-northeast relative to the hotspot forming the chain that includes Alejandro Selkirk and Robinson Crusoe islands. The white arrow shows the direction of motion of the Nazca Plate relative to the hot spot, and it is nearly indistinguishable from the direction predicted from global plate motions relative to all the hot spots on the planet (green arrow). The similarity in direction indicates that very little motion of the Juan Fernandez hot spot relative to other hot spots is needed to explain its trend. Illustration by Chengzu Wang

Gordon, lead author Chengzu Wang and co-author Tuo Zhang developed a method to analyze the relative motion of 56 hot spots grouped by tectonic plates. They concluded that the hot-spot groups move slowly enough to be used as a global reference frame for how plates move relative to the deep mantle. This confirmed the method is useful for viewing not only current plate motion but also plate motion in the geologic past.

The study appears in Geophysical Research Letters.

Hot spots offer a window into the depths of Earth, as they mark the tops of mantle plumes that carry hot, buoyant rock from deep Earth to near the surface and produce volcanoes. These mantle plumes were once thought to be straight and stationary, but recent results suggested they can also shift laterally in the convective mantle over geological time.

The primary evidence of plate movement relative to the deep mantle comes from volcanic activity that forms mountains on land, islands in the ocean or seamounts, mountain-like features on the ocean floor. A volcano forms on a tectonic plate above a mantle plume. As the plate moves, the plume gives birth to a series of volcanoes. One such series is the Hawaiian Islands and the Emperor Seamount Chain; the youngest volcanoes become islands while the older ones submerge. The series stretches for thousands of miles and was formed as the Pacific Plate moved over a mantle plume for 80 million years.

Rice University geophysicists have developed a method that uses the average motion of hot-spot groups by plate to determine that the spots aren’t moving as fast as geologists thought. From left, Chengzu Wang, Richard Gordon and Tuo Zhang. Photo by Jeff Fitlow

The Rice researchers compared the observed hot-spot tracks with their calculated global hot-spot trends and determined the motions of hot spots that would account for the differences they saw. Their method demonstrated that most hot-spot groups appear to be fixed and the remainder appear to move slower than expected.

“Averaging the motions of hot-spot groups for individual plates avoids misfits in data due to noise,” Gordon said. “The results allowed us to say that these hot-spot groups, relative to other hot-spot groups, are moving at about 4 millimeters or less a year.

“We used a method of analysis that’s new for hot-spot tracks,” he said. “Fortunately, we now have a data set of hot-spot tracks that is large enough for us to apply it.”

For seven of the 10 plates they analyzed with the new method, average hot-spot motion measured was essentially zero, which countered findings from other studies that spots move as much as 33 millimeters a year. Top speed for the remaining hot-spot groups — those beneath the Eurasia, Nubia and North America plates — was between 4 and 6 millimeters a year but could be as small as 1 millimeter per year. That’s much slower than most plates move relative to the hot spots. For example, the Pacific Plate moves relative to the hot spots at about 100 millimeters per year.

Gordon said those interested in paleogeography should be able to make use of the model. “If hot spots don’t move much, they can use them to study prehistorical geography. People who are interested in circum-Pacific tectonics, like how western North America was assembled, need to know that history of plate motion.

“Others who will be interested are geodynamicists,” he said. “The motions of hot spots reflect the behavior of mantle. If the hot spots move slowly, it may indicate that the viscosity of mantle is higher than models that predict fast movement.”

“Modelers, especially those who study mantle convection, need to have something on the surface of Earth to constrain their models, or to check if their models are correct,” Wang said. “Then they can use their models to predict something. Hot-spot motion is one of the things that can be used to test their models.”

Gordon is the W.M. Keck Professor of Earth Science. Wang and Zhang are Rice graduate students. The National Science Foundation supported the research.

 

Read the paper at http://onlinelibrary.wiley.com/doi/10.1002/2017GL073430/full