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How Was the Grand Canyon Formed?

Geology | Rock and Minerals

Grand Canyon Age

Like a stack of pancakes, young rock layers pile on top of older layers. From top to bottom, you are passing through about 2 billion years of time. We use the superposition and relative dating to find when rocks were deposited.

Have you ever been to the Grand Canyon before? It’s a remarkable site for geology and Earth’s history.

What I always liked about going there was counting all the layers of rock along the steep-sided canyon.

Little did I know, I was counting through the layers of Earth’s history. If I knew when the layers of rock were deposited, I could even estimate Earth’s age.

How to use relative dating to estimate age

Rocks always tell a story. Because younger sedimentary rocks stack on top of older rocks, we use relative dating (superposition) to chronologically order events in the past.

For instance, they reveal stories about colliding continents, meandering streams and volcanic eruptions.

In the case of the Grand Canyon, the multi-layered strata provide insight into the age of the Earth.

We are able to see cross-sections because the Colorado River started cutting through the Grand Canyon about 6 million years ago. Even today, these erosional forces are still at work.

Unconformities are time gaps in the rock record. This is where rocks have eroded away and we are actually missing rocks without evidence of any record for that time.

How old are the sedimentary rocks for the Grand Canyon?

Grand Canyon Layers

The Grand Canyon is a prime example of rock superposition and relative dating. Continuous horizontal layers of rock are repeated throughout time.

They mostly consist of marine sediments that formed in oceans through compaction. From top to bottom, the Grand Canyon is essentially three main types of sedimentary rocks – sandstone, limestone and shale.

  • SANDSTONE: Sandstone is compacted sand like you can find at a beach.
  • LIMESTONE: Limestone contains large amounts of formerly organic material such as plants, shells and clams.
  • SHALE: Shale begins as mud and gets compacted to form a flakey type of rock.

The base of the Grand Canyon is Precambrian basement rocks. These were formed from flowing magma which cooled and hardened about 1.8 billion years ago.

In the table below, you can find the formation of Grand Canyon rock layers which date back to 2 billion years. As you can see, most of the rocks are sedimentary like shale, limestone and sandstone.

What are the rock layers part of the Grand Canyon?

Rock Layers Time (Years) Thickness (Meters) Depositional Type
Kaibab Limestone 250,000,000 91-150 Shallow Marine
Toroweap Formation 255,000,000 61 Shallow Marine
Coconino Sandstone 260,000,000 20 Eolian Sand Dune
Hermit Shale 265,000,000 91 Coastal Swamp
Supai Group 285,000,000 300 Shallow Marine
Surprise Canyon 320,000,000 122 Coastal Estuary
Redwall Limestone 335,000,000 137 Offshore Shallow Marine
Temple Butte 350,000,000 30 Tidal Shallow Marine
Muav Limestone 515,000,000 198 Offshore Shallow Marine
Bright Angel Shale 530,000,000 152 Near Shore Shallow Marine
Tapeats Sandstone 545,000,000 70 Intertidal Marine
Chuar Group 825,000,000 1,600 Shallow Marine
Nankoweap Formation 1,050,000,000 110 Shallow Marine
Unkar Group 1,250,000,000 1,950 Shallow Marine
Vishnu Schist 2,000,000,000 Unknown Metamorphosed

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