Wyoming Spring Creek: Ancient and Modern Earth

Wyoming is full of remarkable landscapes: sweeping prairies, colorful badlands, and towering granite peaks, all teeming with diverse plants and wildlife. These ecological communities are an important resource for our studies here, but they sometimes distract us from the vast expanse of ancient ecosystems that are right at our feet. Here you can see layers upon layers of rock, each with their own story to tell of a world before humans walked the earth. During the last three weeks, I have learned how to read these stories and place them in the larger context of Earth’s history.

Analyzing the details of a rocky outcrop is a time-consuming process, but it is vital to understanding the prehistoric ecosystem. The type of rock (igneous, metamorphic, or sedimentary) and its mineral composition, the patterns in its layering (“bedding” in geologic terms), how eroded it is, whether it is tilted and in what direction–all of these tell us how and when the rock formed. Most of the rocks we’ve studied here are sedimentary; they were deposited millions of years ago, some by ancient seaways and rivers, some by wind, and they contain fossils of their respective eras and environments. We only find dinosaur bones, for example, in the Morrison Formation, which is a layer of colorful mudstone, limestone, and sandstone formed during the Jurassic Period. The formations immediately older and younger than the Morrison (Sundance and Cloverly, respectively) do not contain dino fossils because they formed in aquatic environments; dinosaurs lived on land, and the Morrison is a terrestrial deposition. This sequence of formations also leads to many questions: why did the ancient seaway recede? What happened to the marine organisms whose fossils we see in the Sundance Formation? Why is the type of deposition in the Cloverly different than in the Sundance if both were watery environments? These are the kinds of questions we need to ask if we are to understand Earth’s history.

Studying geologic history and paleontology also helps us understand our present-day ecosystems. Depositional patterns vary by environment, and analyzing them may allow us to predict the kinds of rock we will see in the future. Fossil organisms allow us to study and trace common ancestry, origins of species, and extinction events. We can even test marine rock compositions to observe the effects of climate change on the ancient Earth, and use the order of formations to predict what may happen with modern-day climate change. There is astronomical value to studying the ancient Earth, as there is plenty about the modern world that we would not understand otherwise.

An overlook at Alcova Reservoir, a famous spot for finding fossils and studying formations of the Mesozoic Era. The top layer here with the large boulders is part of the Cloverly Formation, which is made of conglomerate sandstone, a type of rock deposited in a high-energy aquatic environment such as a fast-moving riverbed. Below it are the characteristic purples and greens of the Morrison Formation.

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