grand canyon

Have you seen the pictures of these huge sizes and layers of pinkish, golden, and orange rocks? That's the Grand Canyon. 

The Grand Canyon is a steep-sided canyon cut by the Colorado River in the high plateau region of northwestern Arizona, United States. It is 277 miles (446 km) long, a mile (1.6 km) deep, and up to 18 miles (29 km) wide. Over the years its huge size and layers of pinkish, golden, and orange rock (called “strata”) have given the spot major star status around the world.

Do you know the Grand Canyon is up to 6.000 feet deep in certain places? This means one can fit 19 Statues of Liberty stacked on top of each other. Well, you make think, it may be the deepest canyon in the world. But, surprisingly, it isn't. The Yarlung Tsangpo Grand Canyon in Tibet plummets to a depth of 17,567 feet, making it more than 2 miles deeper than the Grand Canyon. The Tibetan Canyon is also about 30 miles longer than the Grand Canyon. 

How was the Grand Canyon formed?

Scientists estimate the canyon may have formed 5 to 6 million years ago when the Colorado River began to cut a channel through layers of rock. Wind and rain have helped the erosion process. This phenomenon shows how consistent weathering and erosion over a long period of time can radically shape the earth.

The first Europeans to reach the Grand Canyon were Spanish explorers in the 1540s. Later in 1893, President Benjamin Harrison first protected the Grand Canyon as a forest reserve, and in 1919 it became an official United States National Park. 

A trip down into the Grand Canyon is literally a trip back in time written on the rocks.

Humans have inhabited the area in and around the canyon since the last Ice Age.

Rocks of the Grand Canyon

The ages of Grand Canyon's rocks span over 1.5 billion years of Earth's history. During his expeditions of the Grand Canyon in the late 1860s and early 1970s, the explorer and scientist John Wesley Powell, first described the three main sets of rock layers in the Grand Canyon. These are: 

• Metamorphic Basement Rocks
• The Grand Canyon Supergroup
• Paleozoic Strata 

These rock layers have given geologists the opportunity to study evolution through time.

Metamorphic Basement Rocks

The oldest known rock in Grand Canyon, known as the Elves Chasm Gneiss, is found at the bottom of the canyon. These rocks are primarily metamorphic with igneous intrusions. The name given to this rock set is Vishnu Basement Rocks. The Vishnu rocks formed about 1.7 billion years ago, from an era early in Earth history known as Proterozoic. These tell the story of the creation of North America when volcanic islands collided with the continental landmass. 

The Grand Canyon Supergroup

The middle rock set is called the Grand Canyon Supergroup. It is primarily sandstone and mudstone, both sedimentary rocks, with some areas of igneous rock. These rocks are from the late Proterozoic. They do not contain many fossils, because they formed before complex life on Earth was common. 

The rock layers in the Grand Canyon Supergroup are tilted, whereas the other rocks above this set are horizontal. This is known as an angular unconformity. The top of these sediment layers was then eroded away, forming the Great Unconformity. 

Paleozoic Strata

These are layers are sedimentary and primarily sandstone. The typical reddish layers that you often see in the images of the Grand Canyon are made up of this set of rocks. This set is much younger than the other rock layers, following the Great Unconformity. Fossils are prevalent in this layer. This set tells us that the region was a warm, shallow sea when these sediments were deposited. 

The Kaibab Formation is the youngest of Grand Canyon's rock layers. It forms the rims of the canyon and is a mere 270 million years old. Well, that's much before the dinosaurs roamed the Earth!

"Unconformities" are common in the Grand Canyon

At times, rocks or sediments are eroded away and time elapses before new deposition occurs. These results in gaps in the geologic record known as "Unconformities". While the new sediments deposit on top of the eroded surface and eventually form new rock layers, there is a period of geologic time that is not represented. "Unconformities" are like missing pages in the book.

The Grand Canyon offers one of the most visible examples of the Great Unconformity, which are common in the Grand Canyon Supergroup and the Paleozoic Strata. In these 250 million-year-old rock strata lie back-to-back with 1.2 billion-year-old rocks. What happened during the hundreds of millions of years between remains largely a mystery. 

The river continues to be an agent of change, reshaping the canyon over time. The canyon isn’t fully formed as long as there is water flowing. 

Fossils found in the Grand Canyon

There are many fossils in the Paleozoic Strata that help scientists learn about the geologic history of North America. Most of the fossils are ocean-dwelling creatures that tell this area in Arizona was once a sea.

Some of the most common fossils found in the Grand Canyon are: 

Trilobites	These were invertebrates that lived in shallow marine environments and varied widely in size. They are index fossils for the Paleozoic, and were particularly prominent during the Ordovician.
Tracks and burrows	These are known as trace fossils because they are not the preservation of the actual organism, but instead, show where the organism moved and lived. They are commonly dug by trilobites and worms in muddy ocean sediment.
Brachiopods	They left shells behind that are quite common in Paleozoic rocks.

People in the Grand Canyon

Prehistoric humans first settled in and around the canyon during the last Ice Age, when mammoths, giant sloths, and other large mammals still roamed North America. Large stone spear points provide evidence of early human occupation. 

Ancestral Pueblo people—followed by Paiute, Navajo, Zuni and Hopi tribes—once inhabited the Grand Canyon. When the Grand Canyon became a national park in 1919, Native Americans were forced off of large parts of their land. Today, tribes like Havasupai and Navajo, dwell just outside the borders of Grand Canyon National Park.

In their language, Havasupai means “people of the blue-green waters,” for the famous blue-green waterfalls that cascade down Havasu Creek. The people continue their traditional lifestyle in the canyon, and are well known for their peach orchards, strong agricultural practices, and skilled hunting abilities.

Five ecosystems in the Grand Canyon

When we picture the Grand Canyon, we think of bare rocks, but actually, this area is teeming with life. The great variation in elevation and the movement of the river supports five distinct ecosystems with different species thriving in each. From highest elevation to lowest elevation, these five major ecosystems are: 

1. Mixed conifer or boreal forest ( highest elevation)

• It is only found at the highest elevation of the Grand Canyon, at the North Rim, from 8200-9200 feet. 
• It contains deciduous trees like aspen as well as evergreen trees like fir and spruce, which provide a thick forest that shelters animals from intense storms.
• Small mammals like deer, voles, and squirrels are common. 
• This ecosystem receives more rain than any other in the Grand Canyon and averages 11 feet of snow a year. 

2. Ponderosa pine forest

• It is at the second-highest elevations and found on both the South and North Rims. 
• It receives an average of five feet of snow each year, but in the summer is subjected to intense thunderstorms that create flash floods. The tall trees are common targets of lightning, often causing forest fires that are a natural part of the ecosystem. 
• The ponderosa pine tree is the most common plant here. 
• The Kaibab squirrel is endemic (only found in one location) to this ecosystem, and relies on the pine cones for food and the branches for shelter. 

3. Pinyon juniper woodland

• It is found in sunny areas below the North and South rims. 
• This ecosystem gets quite hot in the summer, with these short trees providing the only shade. 
• It has drought-resistant plants, the most common being Utah juniper and pinyon pine. 
• The leaves on the plants here have certain adaptations to capture and retain water, including being scale-shaped or needle-like
• It is sometimes referred to as 'pygmy woodland' because trees do not grow more than 20 feet tall. 
• Common animals are bobcats, and small mammals like rabbits, mice, and skunks. 

4. Desert scrub

• It is the hottest and driest of all and is found only at very low elevation. 
• All the water from the higher elevations evaporates before reaching here. 
• Plants are adapted to unpredictable and scarce water supply - they are smaller with agave being an exception. 
• Common plants include cacti, sage, yucca, and blackbrush
• Common animals include mammals like bighorn sheep and mice, and reptiles like collared lizard. 

5. Riparian or river edge (lowest elevation)

• It is found along the banks of the Colorado River at the bottom of the canyon, by small creeks or springs around the Grand Canyon, independent of elevation. 
• There is a constant presence of water, so they are composed of lush vegetation, including cottonwood trees. 
• While there is the smallest ecosystem, the greatest biodiversity is supported here in both aquatic and terrestrial organisms. 
• Common animals include skunks and canyon tree fogs. Canyon tree frogs are only found in the riparian zone because they depend on a constant supply of water.