The DIG Field School - Exploring Paleontology!

It’s just about every child’s dream to dig for fossils, and this year I got to fulfill my lifelong goal of doing paleontology field work! Thanks to program director Dr. Sterling Nesbitt, Dr. Michelle Stocker (a phytosaur expert), and the Virginia Tech Paleo team, the DIG Field School program expanded into Petrified Forest National Park where during the Triassic, a large river system helped preserve huge forests of trees. In this humid, tropical environment, giant amphibians, reptiles, fish, and early dinosaurs lived and died – and their fossils can be found in and around the park! 

On a side note, did you know that the term ‘dinosaur’ actually refers to a very small percentage of vertebrate fossils that have been found? Scientifically speaking, a dinosaur is an ancient reptile that appeared when birds and crocodiles split on the evolutionary tree - they are on the arm that evolves into birds. Creatures like mosasaurs, pterodactyls, dimetrodon, and plesiosaurs aren’t technically dinosaurs. It’s more accurate to call all those ancient animals ‘archosaurs’.

The program began when we were picked up from the airport in Phoenix by Sterling, the program director. He is a professor at Virginia Tech studying vertebrate morphology – ie the body shapes and how they evolve, and he told us all about the geology of the northern Arizona landscape during our 4+ hour drive to Petrified Forest. For the most part, paleontologists are also geologists – they can read the area’s stratigraphy and identify the origin and composition of the rock. The main thing to remember is the Law of Superposition – that lower layers of soil were laid down first, so deeper layers are older than the ones above.

Geologists divide the rock layers based on different characteristics, and between each layer there must be an definable change.  Petrified Forest (PEFO), where we were doing most of our work, is entirely in the Chinle Formation – formed during the Upper Triassic period of the Mesozoic Era – ie. between 208 and 227 million years ago. This is early in the age of dinosaurs, who lived primarily in the Mesozoic between 250 to 66 million years ago. 

This may sound like a really long time ago, but we soon learned that Earth’s geologic time scale is reaaaaaallllly long. This was clearly demonstrated on our first full day, during our visit to the Grand Canyon.

GRAND CANYON NATIONAL PARK – UNDERSTANDING DEEP TIME

During the past 2 billion years, igneous, metamorphic, and sedimentary rock were deposited to form the layers of the Grand Canyon region. Through uplift caused by plate tectonics, the entire area was pushed upwards and eroded into a giant flat area, forming the Colorado Plateau. The Colorado River then began carving away a canyon as it traveled downstream,  exposing the underlying rock layers - and that's what we came here to see. We traveled to the park to meet with Ranger Brandi Stewart, who coincidentally was the same ranger I met with during my trip to Death Valley NP 5 years ago.

Hi Ranger Brandi!

There are a few misconceptions about the Grand Canyon that Ranger Brandi wanted to address. The biggest misconception by visitors to the South Rim is that it is cooler at the bottom of the canyon than on the rim. Quite the contrary – for every 1000 feet of elevation down, you gain about 5° F in temperature. So the bottom of the canyon is about 25° hotter than where we were standing – an important thing to remember if you’re hiking down to the river! And a good thing for me to know, since I’ll be rafting the Colorado River in about 2 weeks...

Two other misconceptions that students have are that rocks don’t change and that rivers passively flow – both of which can be debunked looking at the Grand Canyon.

Most interestingly, Ranger Brandi helped us understand Deep Time. It’s hard to conceptualize the huge numbers used to describe the age of the Earth and the things on it, since 100 million years and 2 billion years both just seem like… well, a loooong time. But there's a big difference between the two, and a lot a time that has passed between now and the formation of the Grand Canyon and the creation of the Earth. A great way to visualize it is to think of the timeline of the earth on our outstretched arms. The earth is about 4.55 billion years old, so if the creation of earth is on our left fingertip, the creation of the Basement rock – the very oldest bottom layer of the Grand Canyon – would be at our right shoulder. Dinosaurs appear at around the knuckle of our right middle finger, and humans don’t show up until the very tip of our fingernail!

4.5 km later,
waaaayy into the past

The start of the walk,
representing present day

The best part of the visit was the Trail of Time - a 4.5 km walk along the canyon rim, with ground markers indicating the passage of time. At the beginning, every meter had a brass marker representing the passage of one year. As you move down the trail, it logarithmically increases until each step equals one million years. By the end, we've walked back in time 2 BILLION years! And the best part is that they actually went into the canyon and brought up sample rocks from different strata and placed them on their birthdays, so you can see and feel how different the layers actually are.

Looking down into the Grand Canyon is like looking back in time – the very bottom rocks of the inner gorge are ancient igneous and metamorphic rocks known as Vishnu Schist, about 2 billion years old. And where we’d be fossil hunting at Petrified Forest, the Chinle Formation is actually younger than the top layer of the Grand Canyon so it wasn’t even visible from the South Rim! It's also interesting to note that the canyon itself was carved rather recently - only over the last 5 or 6 million years.

While it was hard for me to identify individual strata along the canyon walls, it was easy to spot different layers through the varying textures and colors of the cliffs. One of the most interesting and important things to note was that there are huge periods of missing time – known as unconformities. This could be because it was a period of weathering and erosion and the layer has been destroyed, or it was because the environment at the time wasn’t conducive to creating the rock. So when we look at the sides of the Grand Canyon, there is actually more time that is missing than there is represented in rock!

Seeing the actual layers of time exposed at the Grand Canyon was a great introduction to geology, and helped us understand how rock can tell the story of the past. 

A fun dinner stop in Winslow, Arizona with teacher Molly

Welcome to Camp!

We returned that night to camp in Petrified Forest National Park, our home for the next four nights. Our tents were set up on the old Civilian Conservation Corp campground near the Rio Puerco, where the CCC first stayed in the 1930s. At the time, young men looking for work during the Great Depression helped build up the park's infrastructure by paving roads, creating trails, and building the park's museum, headquarters, and ranger housing. 

We were some of the only people to camp inside the park since PEFO has no public campsites, so it was a privilege to stay there!