A new electron microprobe that can determine the date and history of any rock without crushing the sample has been developed by two researchers at the University of Massachusetts. The new method offers greater efficiency and access to a much more detailed geologic record than current dating methods, the scientists said.

Geologists Michael Williams and Michael Jercinovic have just won funding for development of the new electron microprobe after the success of early tests. The National Science Foundation provided a $450,000 grant as part of a $1.2 million project to develop and construct a new specialized electron microprobe for geologic dating.

Funding for the collaborative project has also been provided by Cameca Inc., a developer of analytical instrumentation, and the University of Massachusetts.

The new microprobe being built at Cameca's lab in Paris will be housed in the University's department of geosciences next spring. It will have applications throughout Earth and planetary science as well as in fields as diverse as microelectronics, forensic science, fiber optics, and even microbiology, Williams said.

"Looking at the entire lifespan of a sample, rather than just tagging it with an average age, is critical," said Williams. "It's the difference between having a single snapshot or a lengthy, detailed videotape of a series of events. We don't want to know just where and when a rock was formed, but also when and where it was buried, deformed, heated, melted, and eventually exhumed to the Earth's surface," he said. "We want to determine the life history of each rock and then combine these histories to understand the geologic history of a region of the Earth."

Scientists using conventional methods such as radiometric dating can determine the age of a rock sample within 5 million to 10 million years. But there are limitations. The samples must be crushed and the grains of radioactive minerals extracted. They are then placed into a mass spectrometer that can measure isotopes.

Current methods are labor intensive, requiring tens of hours to examine a single sample. There are some samples that scientists are reluctant to crush such as moon rocks or rocks containing fossils.

Also, Williams said, crushing a rock mixes the crust and the center, yet different parts of a rock may have different ages because rocks typically record a progression of events which may involve melting, deformation, or reheating within the Earth's crust. Dating a whole crushed rock leaves scientists with an average age rather than pinpointing the ages of specific events in a rock's history.

"We actually take a rock and cut a slice of it and insert it into the probe," Williams explained. "We direct our electron beam at the particular mineral of interest to make the measurement. It is far faster than the traditional method." The new microprobe could reduce uncertainty of date to 1 million years.

Williams is a field geologist with a special interest in the Canada's Laurentian Shield and Arizona's Grand Canyon. Study of these areas could particularly benefit from the microprobe.

In the Grand Canyon, said Williams, there are rocks that are 700 million years old. "Those may be associated with the snowball Earth time. When the whole Earth froze, it stimulated the evolution of modern life," he said. "We think we've found rocks in the Grand Canyon that occured about this time.

"The great bloom of life when we went from ocean to land happened 600 million years ago," said Williams, who is collaborating with Sam Bowring at the Massachusetts Institute of Technology to investigate this blossoming of life after a freeze, known as the Cambrian Bloom of Life.

The new techniques, called "high-resolution age mapping and microprobe dating," involve the analysis of monazite, a mineral that is present in many rocks but in very small quantities. It is widely used in radiometric dating because it contains the elements thorium and uranium, which decay to the element lead at a known rate. "Monazite essentially provides us with a stopwatch for timing geologic events in different areas of rocks," Williams said.

Williams and Jercinovic have used the basic technique with the existing electron microprobe at UMass to investigate the growth of the North American continent, its interaction with other continents to make supercontinents, the eruption of volcanoes, and the history of the Appalachian Mountains.

The electron microprobe can be applied to materials older than 100 million years. The technique can be used to solve problems of Earth's evolution but not to date humanoid fossils, which are far too young, said Williams.

Reading the record of materials the Earth provides — and particularly the record of plate tectonics — is critical, Williams said. These phenomena open our understanding of the development of Earth's crust, the evolution of climate throughout Earth's 4.5-billion-year history, and how human beings and different species of animals spread across the planet.

Williams said, "If we can read the past, we have a better chance to understand the future."