Chances are, fellow cacher, if you are driving down this highway you are going to, or coming back from, Big Bend. And if you are going to Big Bend, chances are you are going for the scenery - which really means the geology, of this incredible part of the country. And when you find out about the geology, chances are you will hear about the rocks and formations in regards to the Geological Time Scale. What that is, and being able to tie that to real world examples, is often difficult, and the meaning of the time scale can be lost to the casual geology fan (which you are, if you do earthcaches!) This earthcache will not only teach you about the time scale, but also gives you a unique opportunity to see examples from the last three eras along the way!
The Geological Time Scale is split up into large blocks of time (known as eras). These eras are further divided into medium blocks of times (known as periods). Finally some of the periods are further divided into small blocks of time (known as epochs). The time spans of these categories can vary greatly, and are generally determined through identifying and classifying features (such as fossils) found in the rock layers. (They are subdivided even more than this, but I'm keeping it simple for us non-Geologists!) Once a Geologist has identified a formation's origin along the Geological Time Scale, they can make predictions about the fossils, crystals, minerals, etc contained within the structure.
The Geological Time Scale
Precambrian Era
Hadean Period - From the origin of the Earth about 4,500 million years ago to about 3,800 million years ago
Archean Period - 3,800 million years ago to 2,500 million years ago
Proterozoic Period - 2,500 million years ago to 540 million years ago
This is the earliest and by far the longest block of time in the history of the Earth, lasting about 4 billion years. At this time the earth forms, cools, oxygen builds in the atmosphere and the beginnings of life are established. MOST of the history of the Earth is in the Precambrian.
Paleozoic Era
Cambrian Period - 540 million years ago to 505 million years ago
Ordovician Period - 505 million years ago to 438 million years ago
Silurian Period - 438 million years ago to 408 million years ago
Devonian Period - 408 million years ago to 360 million years ago
Mississippian Period - 360 million years ago to 320 million years ago
Pennsylvanian Period - 320 million years ago to 286 million years ago
Permian Period - 286 million years ago to 245 million years ago
A huge diversification of life begins in what is called the Cambrian Explosion. Animals and plants began to appear and diversify, and much of the fossils and minerals we use today (such as oil, chalk, etc) are formed. Also land masses join to create the supercontinent of Pangaea.
Mesozoic Era
Triassic Period - 245 million years ago to 208 million years ago
Jurassic Period - 208 million years ago to 144 million years ago
Cretaceous Period - 144 million years ago to 65 million years ago
Dinosaurs! Also flowering plants, crocodilians and the early, small mammals are found in the fossil records. Pangaea breaks apart and continents drift away. This Era famously ends with the end of the dinosaurs.
Cenozoic Era
Paleogene Period - 65 million years ago to 23 million years ago. This period is split into the Paleocene epoch, Eocene epoch and Oligocene epoch
Neogene Period - 23 million years ago to 1.5 million years ago. This period is split into the Miocene epoch and Pliocene epoch
* The Paleogene Period and Neogene Period were formerly grouped together into the Tertiary Period, and may still be referred to in this way in older texts and signs
Quarternary Period - 1.5 million years ago to Today. This period is split into the Pleistocene epoch and Holocene epoch
Mammals and the rise of man! Also the Ice Ages come and go, thinning out and rebuilding life over and over.
The Earthcache and requirements
The cache coordinates will bring you to a small picnic area south of Marathon, Tx on U.S. 385. The area around you was formed during the Paleozoic Era approximately 500 million years ago. The highway road cuts through which you pass expose limestone deposited in the Cambrian / Ordovician Periods, and then later raised and exposed through the Marathon Uplift. Notice the folding of the mountains in the area.
Next head to stage #2. As you head south, notice how the geology suddenly changes as you drive. You will find that you will literally descend into a new time, and a new geology. You will descend several hundred feet in elevation onto a plain made of Cretaceous Period limestone (of the Mesozoic Era) - and you will effectively have traveled forward about 350 million years in time. This area was once a swampy, marsh area where an entirely different version of life lived from where you just left. This area was not part of the Marathon Uplift, so the younger Cretaceous limestone is still visible. There is however, another huge geological force at play here - Erosion. Just how much is the question at your next stop.
Once you arrive at Stage #2, please pull completely off the road onto the gravel shoulder. (Marathon is no longer the 'main entrance' to Big Bend, and the highway is very quiet, but please be aware of your surroundings). You will find a sign for Santiago Peak at the Stage #2 coordinates, as well as the Peak's elevation. Santiago Peak is a volcanic intrusion - a formation made when magma travels up through cracks and fissures in the earth but fails to erupt onto the surface. It was formed during the Paleogene Period (of the Cenozoic Era) about 35 million years ago, which means that it was pushing up through the older Cretaceous limestone upon which you stand.
Logging Question - How many feet (minimum) of Cretaceous Period limestone was once above your head in order to cover the top of Santiago Peak? (Take an elevation reading while standing by the sign, then subtract your elevation from that posted on the sign to get your answer.)
All of that limestone has been removed by EROSION!
Email me your answer and log your find!