Welcome to Utah State University's Vertebrate Paleontology course. My name is Benjamin Burger. In this lecture, I'll introduce you quickly to the geological time scale and discuss how it was developed based on fossils.
Now if you're a geologist, you likely have this geological time scale burned into your brain. But let's quickly go over it. For our purposes in this class on fossil vertebrates.
We are interested in the time span from 541 million years ago until the present day, a long period of time called the Phanerozoic Eon. Before 541 million years ago, during the Pre-Cambrian, fossils are microscopic, or single cells, or soft bodied jelly like things that we are not going to study in this class. Now the first skeletons that fossilized are found in the Cambrian. The Phanerozoic Aeon is divided into three airs, the Paleozoic, Mesozoic and Cenozoic, which just means old life, middle life, and recent life. These are further divided into periods.
The Paleozoic from oldest to youngest is Cambrian, Ordovician, Silurian, Devonian, Carboniferous. In the United States, we divide this into Mississippian and Pennsylvanian, and the Permian. The Mesozoic is divided into the Triassic, Jurassic, and Cretaceous periods.
And as you guessed, that was the time of the dinosaurs. The Cenozoic is divided into two different ways. The older way is a tertiary period and a quaternary period, although more recently geologists have divided the tertiary into the Paleogene and Neogene periods. and have retained the quaternary. Because of the dense fossil record in the Cenozoic, we can divide the periods into smaller units called epochs, or epochs.
The Paleocene, Eocene, Oligocene, Miocene, Pliocene, Pleistocene, and Holocene. Now you may be asking yourself, why, where did all these names come from? Why don't we just use dates like historians do? We need to look at how we can age rocks. Imagine that you are looking through your photos of your life in a photo album.
album. You can tell that the photos in the first part of the book are from when you were a little cute baby, followed by being a child, then a teenager, and finally a college student. Maybe it continues on with a marriage, the birth of kids, and finally your kids growing up through time. You can organize your family photo album into distinct periods.
The time when you were a baby, when you started elementary school, when you went off to high school. Now you may easily recall your birth date, but you don't have the exact date for every single photograph. Like, what day was this graduation picture taken?
You don't know. The geological record is the same way. Instead of photographs in an album, we have photographs in a book.
fossils. Each period represents a new set of fossils, and a major event in the history of the planet. So geologists can more easily recall whether a rock is within the Triassic or Permian than they can in giving it an absolute date, such as 255 million years old. Absolute dates often require igneous rocks that don't preserve. fossils, as well as advanced techniques to determine the rock's age in a laboratory setting.
While the simple discovery of a fossil can help establish the date of a rock layer with a fraction of the of the budget and the time necessary for an absolute date. Now there are lots more subdivisions of ages in the rock layers based on fossils. Fossil mammals are used in each continent to construct land mammal ages, which allow correlation of rock units from one basin to another based on the series of fossils found in each layer of rock. Paleontologists use index fossils. Index fossils are organisms that live during a particular geological age and they're used to identify or date the rock.
A good index fossil has four characteristics. First, it is distinctive. Second, it is widespread. Third, it is abundant. And fourth, it is limited in its geological time span that lived during.
Because most fossil-bearing rocks formed in the ocean, the majority of index fossils are marine organisms. Although on land, vertebrates can be used as index fossils for the terrestrial rock record such as rodents or other small common mammals. Alright, be sure to memorize the geological timescale, especially if you haven't learned it before, and indicate how the geological timescale was developed from the specific temporal ranges of fossils.
Alright, thank you for watching. If you like to learn more about the Utah State University geology program, check out the website geology.usu.edu or my own website at benjaminslashburger.org. Links are found in the description below.