UNIVERSITY PARK, Pa. — Jesse Reimink, assistant professor of geosciences, will use a Faculty Early Career Development Program (CAREER) award from the National Science Foundation (NSF) to shed light on how the Earth’s continents took shape between 2.5 and 4 billion years ago.

Many theories exist on how the continents formed, said Reimink. Some believe that the continents formed suddenly by geological time standards about 2.5 billion years ago, while others believe the rocks that formed the continents were shaped long before that, and they continued to reform over time, incorporating new rock into the old.

“The continents are like an onion; we know that the outer layers are younger, the inner parts of continents are older,” Reimink said. “The question is, did the onion grow layer by layer during the past 4 billion years gradually? Or did the onion grow more quickly, reworking and reshaping the layers from past layers, resetting the ages so that they look younger to us?”

Using the five-year, $903,000 award from the NSF, Reimink and his students and collaborators will gather rock samples in five areas of the U.S. known to be about 2.5 billion years old as well as some samples taken from Northern Canada. Samples will then be prepared and evaluated mostly at Penn State’s geochronology lab with some specialty analysis performed at collaborators’ labs.

Reimink will gather specimens roughly the size of two fists and break them down into sediment-size grains. From there begins the search for xenocrysts, or foreign crystals that predate the larger sample.

“In a piece of 2.5-billion-year-old granite, you might have a lot of zircon crystals within the sample telling us that the rock is about 2.5 billion years old,” Reimink said. “But you might have a 4-billion-year-old core telling us that layer of the onion has been overprinted from a much older rock.”

Another method the team will employ is using radioactive dating from certain isotopes — such as neodymium — that were around when the solar system formed but have since decayed away. This past radioactive decay can leave very tiny chemical clues pointing to old continents — the now-gone layers of the onion.

Reimink said two technical developments have made experiments like this more tractable. The laser ablation technique employed at the geochronology lab allows the team to analyze hundreds of mineral grains daily, a process that used to take weeks. And, for the neodymium isotopes, new advanced instruments are producing more precise measurements.

“These techniques have really matured in the past decade,” Reimink said. “Researchers in my field are really pushing the limits to make the measurements more precise so that we can be more sensitive to these signals. It’s something I've been working on for a while to try and improve this technique.”

From an Earth-history perspective, Reimink said, "it’s important to understand how the planet has operated over the past 4 billion years. It’ll advance our quest to answer key questions related to the geodynamics: Did Earth have tectonic plates from the start or did they evolve over time?"

It’s also helpful for planetary scientists — Understanding how the Earth changed over time helps them understand how planets formed and evolved. These more than 2.5-billion-year-old rocks are also where many of the Earth’s treasures such as gold and platinum are mined, added Reimink.

The research will also give undergraduate and graduate students ample field opportunities, which are very important to employers, said Reimink.

“This will give us a chance to do the sort of field work that helped me while earning my Ph.D.,” Reimink said. “Several students will be able to go into the field with a few faculty members and gain a lot of hands-on experience. “Course work is a critical part of the learning process but so is having that extra, more intimate and research-focused field experience.”