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ASU researchers develop new model of Earth's dynamic interior

March 30, 2014

Seeking to better understand the composition of the lowermost part of Earth’s mantle, located nearly 2,900 kilometers (1,800 miles) below the surface, a team of Arizona State University researchers has developed new simulations that depict the dynamics of deep Earth.

A paper published March 30 in Nature Geoscience reports the team’s findings, which could be used to explain the complex geochemistry of lava from hotspots such as Hawaii. ASU graduate student Mingming Li standing in front of computer clusters Download Full Image

Mantle convection is the driving force behind continental drift, and causes earthquakes and volcanoes on the surface. Through mantle convection, material from the lowermost part of Earth’s mantle could be carried up to the surface, which offers insight into the composition of the deep Earth. The Earth’s core is very hot (~4000 K), and rocks at the core mantle boundary are heated and expand to have a lower density. These hot rocks (also called mantle plumes) could migrate to the surface because of buoyancy.

Observations, modeling and predictions have indicated that the deepest mantle is compositionally complex and continuously churning and changing.

“The complex chemical signatures of hotspot basalts provide evidence that the composition of the lowermost part of Earth’s mantle is different from other parts," explains lead author Mingming Li, who is pursuing his doctorate in geological sciences. "The main question driving this research is how mantle plumes and different compositional components in Earth’s mantle interact with each other, and how that interaction leads to the complex chemistry of hotspot basalts. The answer to this question is very important for us to understand the nature of mantle convection.”

“Obviously, we cannot go inside of the Earth to see what is happening there," says Li. "However, the process of mantle convection should comply with fundamental physics laws, such as conservation of mass, momentum and energy. What we have done is to simulate the process of mantle convection by solving the equations which control the process of mantle convection."

It has long been suggested that the Earth’s mantle contains several different compositional reservoirs, including an ancient, more-primitive reservoir at the lowermost mantle, recycled oceanic crust and depleted background mantle. The complex geochemistry of lava found at hotspots such as Hawaii are evidence of this. The various compositional components in hotspot lava may be derived from these different mantle reservoirs. The components could become embedded in and carried to the surface by mantle plumes, but it is unclear how individual plumes could successively sample each of these reservoirs.

Joined by his adviser Allen McNamara, geodynamicist and associate professor in ASU’s School of Earth and Space Exploration, and seismologist and SESE professor Ed Garnero, Li and his collaborators’ numerical experiments show that plumes can indeed carry a combination of different materials from several reservoirs.

According to the simulations, some subducted oceanic crust is entrained directly into mantle plumes, but a significant fraction of the crust – up to 10 percent – enters the more primitive reservoirs. As a result, mantle plumes entrain a variable combination of relatively young oceanic crust directly from the subducting slab, older oceanic crust that has been stirred with ancient, more primitive material and background, depleted mantle. Cycling of oceanic crust through mantle reservoirs can therefore explain observations of different recycled oceanic crustal ages, and explain the chemical complexity of hotspot lavas.

“Our calculations take a long time – more than one month for one calculation – but the results are worth it,” says Li.

Nikki Cassis

marketing and communications director, School of Earth and Space Exploration

3 outstanding ASU juniors win Goldwater Scholarships

April 1, 2014

Three outstanding Arizona State University juniors who already are doing sophisticated research have won Goldwater Scholarships, the nation’s premier awards for undergraduates studying science, math and engineering.

Working in the laboratories of ASU senior faculty and scientists, the students carry out research ranging from developing biosensors for early detection of infectious diseases to conducting microelectronics research at ASU’s Flexible Display Center. portrait of ASU student Jakob Hansen Download Full Image

Recipients are Ryan Muller of Phoenix, majoring in biochemistry and molecular/cellular biology; Brett Larsen of Chandler, majoring in electrical engineering and physics; and Jakob Hansen of Mesa, a mathematics and economics major. Each of the four will receive $7,500 a year for up to two years.

All are in the College of Liberal Arts and Sciences, while Larsen is also in the Fulton Schools of Engineering. All three are enrolled in Barrett, the Honors College. A fourth student who received honorable mention is Samuel Blitz, a physics major from Scottsdale.

ASU students have won 55 Goldwater Scholarships in the last 21 years, placing ASU among the leading public universities.

Muller is a resourceful and motivated student who began doing research at ASU while still a student at North High School, and again the summer before his freshman year. Xiao Wang, assistant professor in the School of Biological and Health Systems Engineering, remembers that even though Muller was initially the youngest member of the iGEM synthetic biology research team, others quickly began to rely on him.

“His ideas were fresh, innovative and motivating to the team,” says Wang. “In fact, the first day he volunteered in my lab, without any prior experience, he implemented a strategy to effectively screen for bacterial colonies that contained the correct transformed plasmid. The team began to rely on his resourcefulness.”

In subsequent years, Muller continued working on the team and was a key player in helping them develop a portable, low-cost biosensor system to detect pathogens in water supplies. They won a gold medal and a spot in the international championship event for one of the world’s premiere student engineering and science competitions.

Interested in expanding their work, Muller and others assembled a team of undergraduate researchers to seek additional funding. Last year, they were grand prize winners at the ASU Innovation Challenge and at the ASU Edson Student Entrepreneur Initiative. Their fledgling company, Hydrogene Biotechnologies, may help cut down on water-borne diseases that can kill, such as acute childhood diarrhea.

Hansen, a graduate of Red Mountain High School, is a talented mathematician who has been a delight to his professors as someone who enjoys the formal beauty of mathematics, yet is committed to doing research into real problems that affect humans.

“Jakob is exceptionally talented at mathematics, and is one of relatively few undergraduates that I have taught at ASU who was equally enthusiastic about pure and applied mathematics,” says Jay Taylor, assistant professor in the School of Mathematics and Statistical Sciences. “He was always very keen to discuss the theory underpinning the techniques that I presented in class.

“For his project, he wrote a computer program to simulate a malaria outbreak in a small population and used this to investigate the conditions under which malaria will persist in small populations subject to seasonal variation in transmission intensity.”

Hansen participated in ASU’s Computational Science Training for Undergraduates last summer with Rosemary Renaut, professor of mathematics, who praised his mathematical sophistication to the Goldwater committee. He is continuing his research with Renault into more abstract problems.

Larsen, a graduate of Tri-City Christian Academy, received funding early in his career from the Fulton Undergraduate Research Initiative. Over the past two years, he has conducted research at ASU’s Flexible Display Center, developing ultra low-power circuits and applying advanced signal processing techniques to personnel detection along borders and in hostile territory.

Larsen says his interest in science was sparked by a Boy Scout leader, an electrical engineer who talked to him about subjects that enthralled him: objects traveling at the speed of light, the astonishing power of fusion and fission reactions, and theoretical designs for time machines and light sabers. Larsen was inspired to excel in science so he could push the boundaries of technology.

Called “a brilliant young man” by Antonia Papandreou-Suppappola, professor of electrical engineering, Larsen shares his love of science by mentoring a group of engineering freshmen and leading a science club for young children at the Child Crisis Center. In the future, he hopes to focus his work on developing mathematical models for defense applications.

“ASU’s success in the Goldwater competition is in large part due to the excellent opportunities our students have had to do advanced lab research with talented and committed faculty,” says Janet Burke, associate dean for national scholarship advisement in Barrett, the Honors College.

“It goes without saying that the drive and brilliance of the students themselves are both important. I have a top-notch Goldwater committee who do a superb job of selecting the students whose applications will bubble to the top of the pile.”