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Sediment helps us reconstruct ancient geology

Layers of rock
Layers of rock laid down millions of years ago by rivers and floods contains a wealth of fossils, waiting to be discovered.The rock in this region of Montana is sedimentary. That means it was once made up of tiny grains carried by wind or water. Over time, the grains compressed into the solid stone we see today.

Rocks can tell us as much about the environment as fossils can. For instance, we know that the sandstone in this area formed from grains of sand deposited on river banks. Mudstones in this region usually represent floodplains lying next to those rivers. Tracing the location of these types of rock tells us what the land was like at the time the sediment was laid down.

Luckily for us, the sedimentary rocks in the Missouri Breaks are also interspersed with ash beds. As the Rocky Mountains rose, volcanoes spewed ash containing radioactive elements. Measuring those elements today gives us a good idea of the age of the rocks.

Laser “fingerprints” bring ecology and geology together

The fossil-hunting team lands on the banks of the Missouri River in Central Montana.
The fossil-hunting team lands on the banks of the Missouri River in Central Montana.OK, so the rocks tell us what the landscape was like, and the fossils tell us what animals lived there. How can we put them together?

One of the specialties of the Rogers’ research is their study of Rare Earth Elements, or REE. Every fossilization site has a different chemical fingerprint—bones fossilized in a floodplain will contain a different set of elements than those from a river bed. The team vaporizes the microfossil with a laser, and the resulting gas can then be analyzed for its chemical composition. This study brings a new level of detail to our understanding of how and where these fossils were preserved.

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