A Walk Across Time

Landscape photography is simply being in beautiful places and trying to capture what you see and how you feel when you are there. Understanding more about those places gives us an opportunity to take that moment to another level and the science of geology is often central to understanding the world around us. Geology is cool, but having said that, geology can be complex. One of the hardest things to wrap our head around is the concepts of time. The world we live in involves tens of years, not millions or billions of years. As I have shared geologic information with friends and family, struggling with the enormity of time seems to be a recurring theme. In an attempt give this clarity, I made a few pictures to help tell the story of geologic time! 🙂

The earth is estimated to be around 4.6 billion years old. Geologists have broken that time down into eons which are subdivided into eras, further subdivided into periods, then epochs and ages. They then give them names that make no sense to most of us and are hard to remember…go figure! Geologists differentiate layers of rocks based on age, mineral types, color and fossils contained in the rock.  These layers, called “formations” are given names and often identified based on the time period when they were deposited.  The geologic time scale is not random but rather based on significant changes that occurred in the environment that were reflected in the rocks. For example, mass extinctions of the dinosaurs that is the dividing line between the Mesozoic Era and the Cenozoic Era.

 So, in an attempt to explain this, we can take a little walk across time. If we took the age of the earth, 4.6 billion years, and made each year a millimeter, that would draw a path across the United States from Los Angeles to Long Island, NY. Let’s walk this journey, hiking 10 miles per day following the path in Figure 1. The journey would cover 2,858 miles (4,600 kilometers) and take 286 days. If we started on January 1, we would finally reach our destination on Long Island on October 13. Each day we would cover over 16 million years time.

Here are some of the early challenges we would face. For the first month and half, or so, we would be traveling across hot, molten magma because the earth hadn’t yet changed from a liquid to a solid yet. But as we are crossing Arizona and into Colorado, things are finally cooling and the continental crust is beginning to form, which is nice. Another challenge is that we will probably be well into the summer before we can actually breathe because the atmosphere hadn’t accumulated much oxygen, until then. A final challenge is food, we will need to pack a bunch of food for this journey. There wasn’t any forms of life on earth until we reach Pennsylvania, and then it will be pretty limited, mostly single-cell life forms. Wow, the Precambrian time (Hadean/Archean/Proterozoic Eons) making up the first 4 billion years of earth’s history were pretty inhospitable to any forms of life.

The good news, on September 10, already 254 days into our journey, well into Pennsylvania, we finally reached the Paleozoic Era which began 541 million years ago. This is a significant point in geologic time. Life forms, albeit simple forms of life, began to expand and diversify rapidly. Most of the rocks we see today on the surface of the earth were deposited beginning in the Paleozoic Era. The older Precambrian rocks are buried except in a few, generally mountainous, locations where these older rocks have been exposed.

One very famous location where we can find some very old rocks exposed with the younger, Paleozoic rocks layered above is the Grand Canyon. The oldest rocks at the bottom of the canyon are over 1.7 billion years old. Interesting tidbit but the next layer above those older rocks is around 500 million years old, there is 1.2 billion years of missing geologic history that eroded before deposition began again…I digress. The top layer in the Grand Canyon, the Kaibab Limestone, was deposited in the Permian Period of the Paleozoic Era, a little over 250 million years ago. The sediment layers we see in the picture below took nearly 250 million years to deposit. Makes watching the grass grow seem like a hockey game compared to baseball. 🙂 On our journey across the country, we are now approaching New Jersey and nearing the end of September.

Mountains will come, some will go during the Paleozoic Era including; Appalachians, Ouachita Mountains in Arkansas/Oklahoma/Texas, Ancestral Rockies in Colorado, and Antler Mountains in Nevada. Evidence of these events also make some spectacular landscapes. The layered rocks in the “Maroon Bells” is the Maroon Formation, eroded from the Ancestral Rockies originally uplifted 320 million years ago, eroded by 250 million years ago and uplifted again 200 million years later.

Even though we are nearing the end of September on this journey ending on October 13, much is yet to happen. A mass extinction resulting is the demise of over 90% of the marine animal life marked the end of the Paleozoic Era and the start of the Mesozoic Era (252 million years ago). For the next 12 days, we will journey through the “Age of Reptiles” when dinosaurs roamed the world. Remember the movie “Jurassic Park?” During the late Permian and Triassic periods, the continents came together and formed one really big super continent called Pangea. Pangea started breaking apart in the Jurassic. It’s hard to conceptualize how much the continental plates move around but 4″ a year movement, imperceptible to us, is over 63 miles in a million years and over 3,100 miles in 50 million years. Crazy, eh?

On October 9 of our journey and 66 million years ago, a major event believed to be a meteor impact caused another mass extinction ending the Mesozoic Era. This extinction wiped out about 95% of all marine life and 70% of land-life including the dinosaurs and the Cenozoic Era began. Despite having only 4 days remaining in our journey, much of the country was still relatively flat and near sea level. Much is yet to come. The Western Interior Seaway (Figure 3) which divided the country was just starting to recede as the Rocky Mountains began forming. This massive mountain building event across the mountain states was followed by 30 million years of serious volcanic activity across Western North America…and the Antarctic Ice Cap began to form.

I think the most amazing part of this walk through life is the last day. For the last week, we have been east of the Hudson River in New York trekking across Long Island. We have completed 258 days of walking, 10 miles each and every day. On this last day, we have only 8.44 miles to go representing the last 13.58 million years of recent earth history. The star on Figure 3 shows where we slept that last night and how little ground we have left to cover before reaching the present time. So here is how our last day goes:

Early in the morning, faulting out west uplifted the Tetons (10 million years ago). The glaciers that sculpted the mountains and the barn will come around later in the afternoon. 🙂

Early afternoon will bring about uplift on the Colorado Plateau started, yes started, the process of carving the Grand Canyon. But we have all afternoon left, work fast!!

If that is not enough, the last 1.5 miles of your hike would be challenging, and we will need crampons and ice axes because the Ice Ages are now in full swing and Long Island is likely covered by ice. The Pleistocene Epoch starting 2.58 million years ago saw several glacial advances and retreats finally ending 10,700 years ago at the start of the Holocene Epoch. These glaciers left their signature across the mountains, likely carved the great lakes and made the spectacular landscape we see become so special! The U-shaped valleys and cirques (center of pic below) are signature glacial art!!

At the end of the Pleistocene, the glaciers left. The remaining glaciers we see today in the Tetons and Glacier National Park are only 5,000 to 7,000 years old, formed during one of the Holocene cooling cycles depicted on the bottom of Figure 3. The bottom of Figure 3 takes us through the last 18 yards of our journey from nearing the end of the Pleistocene and through the Holocene including the time the early immigrants to North America made the journey. The history of the United States will fit in our last footprint and our lives not much more than our big toe. To put it simply, it all boils down to our big toe!! 🙂

Hope this helps!!