Summary: The vast unit of time known as the
Precambrian started with the origin of the earth about 4.5 billion years ago and ended 570 million years ago. Largely thought to be a hot, steaming, and forbidding landscape, the primitive crust of the newly condensed planet continued to cool. The crust consisted largely of igneous intrusions and volcanic rocks, and sediments that were eroded from this irregular surface.The Precambrian is subdivided, from oldest to youngest, into three eons, the Hadean (4600−3900 million years ago), Archean (3900−2500 million years ago), and Proterozoic (2500−570 million years ago). During the Archean Eon, the earliest living cells formed in the ocean. The
Paleozoic era (570−245 million years ago) was long believed by geologists to mark the beginning of life, because of the sudden abundance of complex organisms with hard parts in the fossil record. These organisms included trilobites and shelled animals called cephalopods. Life was restricted to the sea and included graptolites, brachiopods, bryozoans, and mollusks. By the end of the Paleozoic, all of the continents had come together to form Pangaea. This formation resulted in extreme seasonal weather conditions and one of the greatest periods of extinction in the earth's history—up to 75 percent of amphibian species and 80 percent of marine species disappeared. This time was also marked by the rapid development of land plants, forests of short trees, armor‐plated fishes, sharks, and bony fishes. The Devonian period, the fourth period in the Paleozoic era, is known as the “Age of the Fishes.” Air‐breathing amphibians began to move from the ocean to land. Large tropical swamps dominated much of the landscape. The
Mesozoic era occurred from about 245 million to 66 million years ago. The fossil record from this era (the “Age of the Dinosaurs”) is dominated by a multitude of dinosaur species. By the mid‐Mesozoic, Pangaea rifted into northern Laurasia and southern Gondwanaland. Igneous and volcanic activity formed the mountain ranges in western North America. In the Mesozoic era, new trees such as conifers and ginkgoes appeared. Reptiles laid eggs on land. Dinosaur species included carnivores, herbivores, winged reptiles, and marine reptiles. Mammals were just beginning to emerge during this time. The end of the Mesozoic is marked by more mass extinctions, especially of the dinosaurs. Surviving species included turtles, snakes, crocodiles, and various lizards. The
Cenozoic era, also called the “Age of Recent Life” or “Age of Mammals,” encompasses the last 66 million years of the earth's history. Life forms continued to become more complex. The Cenozoic has the most complete geologic record of any era because it is so recent. The continents were fully separated. Plate tectonic activity created many orogenic and volcanic events in North America, including the western fault‐block mountains and huge lava flows. Eastern North America was tectonically stable, and the Appalachians eroded to lower elevations. Valleys in the western part of the continent were filled with great thicknesses of sediments from the mountain ranges. Waves of mass extinctions occurred toward the end of Pleistocene epoch, including those of mammoths, mastodons, sabertoothed cats, ground sloths, and camels. North America underwent multiple glaciations in the last 20,000 years, which helped mold the landscapes we see today.
Backward-Looking: Does this work tell a story?
When creating a piece of work, no matter what type, you want to be able to tell a story about yourself. When you look at this project, you can or should be able to see my or my groups strengths and weaknesses. If you look closely, there is not be too much information to overwhelm the reader as well as there is art in the background. This shows how our group is good at summarizing and being creative/artistic. Which leads me into my next point. It may not be clear at first, but our group created wheels to show what animals lived during the certain era's. Something none of the other groups did, showing off our creativity. However, you can also see weaknesses in this project. Such as you can tell you worked harder than others in certain parts. In one of the sections of our poster, you can see that there are no plants or animals listed. This can represent procrastination as that group member did not research the plants and animals that were in that era. This project tells a story of how parts of the group may have worked harder than others, but still managed to finish the project with lots of effort and uniqueness.
Inward-Looking: Have you changed any ideas you used to have on this subject?
When first learning of the geologic time scale, I was intrigued as I didn't know anything of earth before the Mesozoic era. However, I was also skeptical because when I hear history of the earth, I think my least favorite subject, history. I've always found history boring, but after this project I've learned not all history is boring. According to the principle uniformitarianism, geologic processes that operate today operated the same way in the past or in other places that have the same conditions. This means that geologic events that happened in the past could most likely occur in the future. Looking at geologic time with this perspective really allowed me to see how important it is and how history can also mean other things.
Outward-Looking: What grade would you give it? Why?
Despite gettng an A on the project itself, I would give it an A-. This is because despite the creativity with the wheels showing the animals and the painting on the board. There were some components missing. Such as on one of the wheels, some of the names were missing. Or on the Precambrian era, despite there being single celled organisms, they were not labeled on the poster. So because of the fact that some components were missing, I would give our project an A-.
Forward-Looking: What's one goal you would like to set for yourself for next time?In the future, or next time, one goal I would like to set for myself is time management. If we had created a calendar or if there was a calendar set in place already would have been a big help. This because we took a whole extra day to research and we missed out on a day were we could've started building our tri-fold. I know it would be a lot of work on the teachers to make a calendar, but some structure so we don't fall behind would be nice. Most often I love to jump into a new project and just begin right away, but if I have a reminder to plan out when my group and I will finish components of the project I think the process of creating the project would be more organized.
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