Wednesday, June 29, 2005
Journey Through Time: Dynamic Forces
Yesterday, we posted an excerpt from a commentary in the Cincinnati Enquirer by a creationist, John Turney. Today, let’s just examine Turney’s first assertion, “all evolutionists, must make assumptions. For example, they assume the Grand Canyon's rock always had its current concrete-like consistency.”
Evolutionists are concerned with biological evolution. It is geologists who undertake the scientific study of the origin, history, and structure of the earth, and it’s specific structural features, such as the Grand Canyon.
Do geologists “assume the Grand Canyon’s rock always had its current concrete-like consistency”? Don’t be silly. Geologists understand that a formation such as the Grand Canyon is the product of dynamic forces. Forces that are still at work today.
Erosion by ice, water, and wind are just some of the dynamic forces that helped carve the canyon. Volcanism, plate tectonics, and the sediments left behind by advancing and retreating ocean coast lines have all played a role in making the canyon one of the most remarkable geological features on earth.
By the way, creationists like Mr. Turney often focus on how rapidly the waters of Noah’s Flood might have carved out the canyon, but they rarely consider how long it took to form the strata there in the first place.
Here’s something else Mr. Turney might not have considered when he wrote his commentary. Many kinds of rock make up the canyon. On our ramble through the canyon, we examined sedimentary, metamorphic, and igneous rock strata. Some of these rocks are much, much harder than concrete. Others are softer. The varying hardness of those rocks, and their resistance to erosion give the canyon its unique profile.
Let’s wander down through the strata now from the South Rim to the river – a journey of 5000 feet and 2 billion years – and take a look at a few of the rock formations, their characteristics and what we – as interested observers – can learn from them.
On the rim, at the Hermit trailhead where Red State Rabble started down into the inner canyon, we first descended through the Kaibab and Toroweap limestones. Both formations are sedimentary strata laid down during the Permian period from 250 to 255 million years ago.
Limestone is made primarily of the mineral calcite from the shells of marine organisms that settled to the bottom of an ancient ocean. These two limestone layers contain the fossils remains of brachiopods, coral, mollusks, sea lilies, worms, and fish teeth.
Geologists – and other reasonable people – can draw a number of conclusions from these simple facts:
- First, that these strata have not always had their current concrete-like consistency. They started first as ooze or slime at the bottom of an ancient ocean that once covered the area where the canyon now sits in all its arid glory.
- Second, we get a rough idea of how long it must have taken for these deposits to form. The Kaibab layer is from 300 to 500 feet thick The Toroweap ranges between 250 and 450 feet thick. (We’ll take a look at how radiometric dating of igneous rocks found in the canyon helps us to know the age of the canyon’s various strata in a later post.)
- Third, we see evidence for evolution in the kinds of fossils found in these strata. For example, no whale fossils have ever been found in Kaibab and Toroweap layers. That’s because the whale did not evolve from its mammal ancestors until much later, in the Eocene epoch, about 40 million years ago.
Further down in our journey through time, Red State Rabble and crew passed through the Coconino Sandstone. The Coconino layer has been called a petrified sand dune. Like the layers above, it is sedimentary, but it was laid down during a period when the ocean had receded, about 265 million years ago. No fossils have been found in this layer, but there are many tracks of vertebrate land animals.
Although it was late September when RSR was there, the temperature in the inner canyon hit 106 degrees and we stopped for a while to rest here. Scroll down to see a photo of reptile tracks preserved on the surface of an ancient dune near where we took our first break in what turned out to be a 12-hour hike.
Below, the Coconino is the Hermit Shale. Mr. Turney doesn’t know this, but the Hermit Shale is very, very soft. Much softer than concrete. You can break small pieces off and crumble them in your hand. Erosion of the shale undercuts the harder layers above causing large blocks to break off and fall onto the Tonto Plateau below.
There are many more sedimentary layers to pass through on the way to the Colorado River. Tomorrow I want to skip ahead to look at the metamorphic and igneous rock formations that can be found in the canyon closer to the river, and what they can tell us about its history.