A man was enjoying the spectacular scenery of the Grand Canyon when an innocuous boulder caught his attention. It looked like any other boulder, but his knowledge told him that the stone held a secret millions of years old. The man snapped a photo and would have never thought that this photo would kickstart a chain of events that would change what we know about Arizona.
The man was Allan Krill, a Norwegian geologist, and the boulder he noticed had fallen from the cliff face alongside the Bright Angel Trail. As Krill took a closer look at the boulder, he began to believe that he had stumbled onto a remarkable discovery that would shine a light on the distant past before dinosaurs walked on the planet. And he was right.
Mind you, the history of the Grand Canyon dates back to nearly two billion years ago. And the landscape of the current state of Arizona started to form when the supercontinents shifted. That's probably when the incredible boulder emerged. But the ravine didn't begin to take shape until towards the end of the Cretaceous Period.
Around 70 million years ago, tectonic plate movements caused the Colorado Plateau to emerge, which ultimately stretched some 130,000 square miles. As the high, flat area rose, melting ice and rainwater trapped in the Rocky Mountains began to leach westwards. And the waterway that formed is what we know today as the Colorado River.
Then, over the following millions of years, the mighty Colorado River raged across the plateau, wearing away the rock below, and as a result, a canyon appeared. Then, roughly two million years ago, several ice ages occurred, causing the river's current to grow even stronger. And this enabled the river to carve a deep groove in the ancient rock, which eventually became the Grand Canyon.
The Grand Canyon reached its current depth around 1.2 million years ago, when the last ice age ended. It's now considered one of the Seven Natural Wonders of the World, but it's far from a complete phenomenon. You see, the powerful Colorado River is still eroding layer after layer of rock, and in the future, the Grand Canyon may become even deeper and wider.
Given the geological activity, you may be surprised to know that humans have had a presence in the region as early as the Colorado River cut the deepest parts of the ravine. Then, over a million years later, the first Europeans came. Nowadays, the unique landmark draws some six million tourists each year.
But tourists aren't the only people flocking to the Grand Canyon. Lots of experts have been attracted to observe the ravine's fascinating geology, and Krill is just one of them. And thanks to these scientists, we now know a great deal about this natural wonder. For instance, the canyon's walls are said to contain at least 13 different types of rock.
Today, some of these rocks become the signatures of the canyon and often take center stage in visitors' snapshots. Two of the most famous are Isis Temple and the Granite Gorge. However, despite the constant flow of visitors and experts, the canyon still holds lots of secrets. In 2014, some geologists challenged the widely accepted theory about the formation of the ravine.
Geologist Karl Karlstrom assessed that the Grand Canyon was far younger than 70 million years old. He wrote in the journal Nature Geoscience, "Different segments of the canyon have different histories and different ages, but they didn't get linked together to form the Grand Canyon with the Colorado River running through it until five to six million years ago."
However, not everyone agrees with his new findings. And more worryingly, there isn't much time left to get to the bottom of things. Geologist Wayne Ranney warned in a 2019 interview that "The Colorado River is constantly tearing away at the walls of the canyon and removing the evidence of its earliest history."
Thankfully, there's also good news. As the canyon's rocks continue to erode, more secrets are being exposed for the first time, including the one Krill unearthed. In 2019, the National Park Service (NPS) discovered a set of fossilized footprints that belonged to a type of tetrapod living in the area around 280 million years ago, even before the dinosaurs walked on Earth.
After studying the ancient tracks, paleontologists concluded that they were Ichniotherium, a type of marking that is typically attributed to diadectomorphs, a clade of tetrapods. More incredibly, they had never been found in desert environments before, so this new discovery shed exciting light on the primitive creatures that roamed the canyon in the distant past.
That same year, the NPS announced that it would compile its largest database of paleontological data ever - a comprehensive catalog of the Grand Canyon's fossil history. It aims to help both experts and the public develop a better understanding of the natural wonder. Even so, some surprises are still there to be revealed, and this takes us back to geologist Krill.
In 2016, Krill took a group of students hiking along the impressive Bright Angel Trail that runs for about 8 miles and drops over 4,000 feet to the Colorado River. Along the way, they passed several famous rock formations, including Brahma Temple and the Cheops Pyramid. But he'd have never expected that he'd be attracted by a far less showy boulder and that as a result he'd change our knowledge about the region's prehistoric life.
Krill spotted the boulder alongside the trail, and on closer inspection, he found a series of strange patterns on the rock's surface. The stone had clearly torn from the Manakacha Formation, a mudstone and limestone cliff running through the canyon. Intrigued by the markings, Krill snapped a photo and sent it to paleontologist Rowland.
After studying the image, Rowland confirmed Krill's suspicion: the patterns were fossilized footprints from the distant past. Two years later, the awe-inspiring discovery was announced at the Society of Vertebrate Paleontology's annual meeting. But it'd take another several years before the details of Krill's groundbreaking find was exposed.
In August 2020, Rowland and two of his colleagues published a paper in the peer-reviewed scientific journal PLOS ONE, where they pinpointed the age of the fossilized tracks with surprising precision. As it turned out, the footprints were around 313 million years old, the oldest fossilized vertebrate footprints ever discovered in the Grand Canyon. But that's not all.
Although scientists aren't sure what exact kind of organism made the footprints, they're sure that it's some type of reptile. And this makes them very special, as Rowland explained in a statement from the NPS. "They are among the oldest tracks on Earth of shelled-egg-laying animals and the earliest evidence of vertebrate animals walking in sand dunes," he stated.
According to experts, the footprints were created back when the now Arizona was a plain close to the Equator; then at some point, two prehistoric creatures walked diagonally across the land, leaving their tracks behind. But there's still been speculation, for example, that the tracks could have been left by the same vertebrate passing through the region at different times.
Whatever the truth, one thing is certain: the two sets of footprints reflect walks at varying speeds. One of the creatures moved using a lateral-sequence walk, a gait Rowland described as being "where the left rear foot moves and then the left front, and then the right rear and the right front and so on."
"Living species of tetrapods - dogs and cats, for example - routinely use a lateral-sequence gait when they walk slowly," Rowland explained in a 2020 interview with The Arizona Republic. "The Bright Angel Trail tracks document the use of this gait very early in the history of vertebrate animals. We previously had no information about that."
But how had the prints managed to stay preserved in such incredible condition for millions of years? Well, that's most probably because they were covered with water and sand. And as time passed, the remarkable treasure remained in the rock within the Manakacha Formation, waiting for the world to shed light on them once again.
However, Rowland's discoveries appear far from conclusive, and they may yet trigger controversy in the paleontological world. "There's a lot of disagreement in the scientific community about interpreting tracks [and] interpreting the age of rocks - especially interpreting what kind of animal made these tracks," the Grand Canyon's Mark Nebel told the Associated Press in 2020.
But for now at least, the boulder Krill noticed alongside the canyon's Bright Angel Trail remains an object of fascination. "A lot of people walk by and never see it," Nebel added, "Scientists, we have trained eyes. Now that they know something's there, it will draw more interest." Surely, Krill's monumental finding will become another attraction in the majestic Grand Canyon.