'Time Machine' Lab Could Propel New Research (6/8/2008)

Like something from the classic H.G. Wells' novel "The Time Machine," a high-precision thermal ionization mass spectrometer will help Texas A&M University geoscientists Franco Marcantonio, Brent Miller and Debbie Thomas explore the ancient worlds of the deep geological past and allow these researchers to determine the ages of rocks that are millions to billions of years old, providing insight into past climates and oceanic circulation patterns.

The thermal ionization mass spectrometer is a key component in the College of Geosciences ' new R. Ken Williams '45 Radiogenic Isotope Geosciences Laboratory, which is set to open in June. The lab will be used for interdisciplinary research and teaching in marine geology and global tectonics.

Philosophers, physicists and astronomers often compare the flow of time to water flowing down a stream - an irretrievable past, a fleeting present and an unknowable future.

"But the past is not entirely erased from existence; it is in some cryptic ways preserved on the Earth in the form of rocks," said Miller, assistant professor of geology and geophysics. "All we need are tools to determine the amount of time represented by the rocks and a way to decode the subtle chemical stories contained within the rock record."

High-tech analytical instruments like thermal ionization mass spectrometers play a key role in revealing those stories. This instrument can detect minute differences in the sub-atomic makeup of many different elements.

"The basic principle behind the mass spectrometer is quite simple and elegant," noted Marcantonio, an associate professor in geology and geophysics. "Atoms of the same element have the same number of protons in their nucleus, but the number of neutrons determines the atomic weight of the atom, and that number can vary. This type of mass spectrometer accelerates atoms along a curved path and through an intense magnetic field. The lighter atoms, or those with relatively fewer neutrons in the nucleus, are deflected more by the magnetic field than the heavier atoms, essentially sorting out the atoms by atomic weight.

"As the sorted atoms exit the magnetic field, they are focused into an array of very sensitive detectors that produce an electrical current in precise proportion to the number of atoms hitting the detector," he added.

Thomas, an assistant professor of oceanography, will use the thermal ionization mass spectrometer to measure minute amounts of the rare element Neodymium in fossil fish teeth, bones, scales and shells of ancient marine microorganisms. According to Thomas, "The chemical signatures of ancient ocean waters are inherited by creatures that lived in those oceans,"

Each Neodymium sample is so small that, in the form of a solid metal particle, 6,000 samples could fit on the head of a pin. Moreover, the mass spectrometer is so sensitive that each sample is plenty for a precise analysis.

Thomas and her students use these measurements to discern ocean circulation patterns from the past when those patterns were driven by differences in climate and in the plate tectonic configuration of the ocean basins. "By understanding past ocean circulation, we can better understand what factors affect or are affected by the oceans, and in doing so gain insight into what may lie ahead as the global climate evolves," said Thomas.

Marcantonio and his students are also examining circulation patterns, including changes in past atmospheric circulation patterns. The distribution of radioactive elements and their stable byproducts in sediments of the deep oceans and shallow coastal regions form a large part of Marcantonio's research. By studying changes in the composition of wind-blown dust in ancient sediments, Marcantonio and his students are able to use the data provided by thermal ionization mass spectrometry to trace changing patterns of atmospheric circulation through time. According to Marcantonio, "Marine sedimentary deposits play an important role in shedding light on past climate change and its effects on past oceanographic and atmospheric processes."

Miller focuses his research on using the mineral zircon to determine the ages of rocks. Zircons are nature's tiny time capsules, acting as a type of clock, faithfully ticking away from the time they are formed until their ratios of radioactive uranium to radiogenic lead are finally measured in a mass spectrometer. Zircons are found in rocks like granite, formed by the crystallization of magma bodies deep in the Earth's crust, and in volcanic ash deposits, erupted from volcanoes like Mt. St. Helens. The former rock type can be used to test ideas about the formation of Earth's great mountain ranges like the Himalayas or the Rockies . The latter is often found interlayered with fossil-bearing sedimentary rocks and can constrain the ages of exotic and extinct life forms.

"Geology is a historical science," said Miller. "It is crucial that we be able to not only put geological events in their correct relative order, but that we can also determine the absolute time spans and rates of those geological events." According to Miller, the new mass spectrometer will allow him to do that.

In contrast to the main character in Wells' novel who traveled into time to explore past worlds, Marcantonio, Miller and Thomas travel the world to explore past times as preserved in rocks and sediments. Those collected samples may reveal different stories but they share the same destiny - chemical separation and purification in the R. Ken Williams '45 Radiogenic Isotope Geosciences Laboratory followed by precise analysis in the thermal ionization mass spectrometer. They will likely propel these researchers and their students a step closer to answering the primal question: How did the Earth work in the deep geological past?

Note: This story has been adapted from a news release issued by Texas A&M University

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