The Grand Canyon Explained | How the Earth Was Made (S2, E1) | Full Documentary | History

The Grand Canyon, a geological marvel in Arizona, holds the secret to Earth's dynamic history. This segment delves into the canyon's formation, highlighting the debate among scientists over its creation. The canyon, a result of continental shifts, volcanic eruptions, and glacial movements, is a testament to the geological forces that have shaped our planet. The mystery lies in the canyon's vastness, carved out of rock by the Colorado River, which raises questions about the river's capability to form such a grand feature despite its size. The narrative also touches on the investigative journey of geologists, like Karlstrom, who follow in the footsteps of John Wesley Powell, to uncover the ancient history of the land and the canyon's formation.

This paragraph explores the ancient geological history of the Grand Canyon, revealing that the site was once home to towering peaks as high as the modern Himalayas nearly 2 billion years ago. Over time, these mountains eroded, and the area was submerged by seas at least eight times, leaving behind a flat plain. The discovery of Vishnu Schist rocks and garnets embedded in these ancient boulders provides crucial clues about the immense pressure and depth at which these rocks were formed. The research indicates that the Grand Canyon region underwent a series of extraordinary changes, from mountains to prehistoric seas, and finally to the uplifted plain that set the stage for the canyon's formation.

The paragraph discusses the geological transformation of the Grand Canyon region, where seas deposited different types of sediment that hardened into various rocks, contributing to the canyon's colorful layers. The dominant red hue comes from iron, which has rusted over millions of years. The calcium content in garnet gemstones suggests that nearly 2 billion years ago, the area was home to mountains comparable to Mt. Everest. The exposed sea fossils indicate that the land was once the muddy bottom of an ancient inland sea. The focus shifts to understanding the forces that transformed this unremarkable flat land into the breathtaking natural wonder that is the Grand Canyon.

This section delves into the geological upheaval that led to the formation of the Grand Canyon. It describes how the Laramide Orogeny caused a major uplift event, raising the rocks without tilting them, resulting in a high, smooth plateau. The Colorado River, which was yet to carve the canyon, had not arrived at this point. The paragraph also discusses the discovery that the ancient riverbed known as Hindu Canyon was not the Colorado River, challenging established geological theories and prompting a reevaluation of the canyon's history. The focus is on the complex geological processes that shaped the landscape, leading to the creation of the magnificent Grand Canyon.

The narrative shifts to the investigation of the Grand Canyon's age and the arrival of the Colorado River. The discovery of pebble alignments in Hindu Canyon by a young geologist named Young in 1969 revolutionized the understanding of the canyon's history. It was found that the river 50 million years ago was not the Colorado, contradicting previous theories. The investigation continued at Muddy Creek near Lake Mead, where limestone deposits indicated the presence of a vast freshwater lake. The extinction of the lake's creatures 5.5 million years ago due to the arrival of the Colorado River provided a confirmed date for the river's arrival and the commencement of canyon excavations. The Grand Canyon was determined to be 5.5 million years old, prompting new questions about the Colorado River's path and the canyon's dimensions.

This segment presents the 'spillover theory' proposed by John Douglass, which suggests that the Colorado River carved the Grand Canyon after a massive lake spilled over the plateau. The theory is tested through a scale model experiment, demonstrating how a small amount of water can gain energy and carve out a canyon over time. Douglass searches for evidence of a lake large enough to cause such a spillover and finds it in the ancient Lake Bidahochi, which once covered 20,000 square miles and contained more water than Lake Michigan. The discovery of deep-water fossils dating back 6 million years supports the theory that the lake existed at the right time to have initiated the canyon's formation. The narrative highlights the ongoing debate among scientists about the forces that shaped the Grand Canyon and the continuous search for evidence to support various theories.

The final paragraph examines the forces that shaped the Grand Canyon's immense width and depth. It explains that the river's erosive power is not due to water alone but the boulders and sand it carries, which erode the rock. The Colorado River's rapid descent over the plateau and its swift flow contributed to the canyon's steepness. The paragraph also discusses the role of gravity and weathering in widening the canyon, as softer rocks crumble away, leading to rockfalls and landslides that increase the canyon's width. The Colorado River's ability to flush debris downstream prevents the canyon from filling up, allowing the continuous retreat of the canyon walls and the growth of the canyon over time. The paragraph concludes by acknowledging the ongoing geological evolution of the Grand Canyon and the persistent efforts of scientists to unravel its complex history.

This section reveals the impact of volcanic eruptions on the Grand Canyon's geological history. Around 725,000 years ago, as many as 100 cinder-cone volcanoes erupted, pouring lava into the canyon and partially filling it. The lava dams created by these eruptions temporarily halted the Colorado River, but eventually, the pressure from the dammed water caused the dams to shatter. The remnants of these lava flows can still be seen today, and some geologists believe that the volcanoes may not be entirely extinct, suggesting future eruptions could further shape the canyon. The narrative emphasizes the dynamic interplay between the Earth's fiery forces and the erosive power of water that has sculpted the Grand Canyon into the natural wonder it is today.