Introduction to Physical Geology Syllabus
faunal succession curtains-and-drapes.info ( bytes). More on index fossils here. Faunal Succession is based on the observation that animals and animal. Superposition. • Correlation by fossils. – Principle of faunal succession. – Concept of index fossil. – Fossil assemblage. • Radioisotopic dating-comparisons . The age of the fossil must be determined so it can be compared to other fossil The principle of faunal succession states that different fossil species always.
Rock that are formed from the transported remains of pre-existing rocks. Rocks that have been chemically altered in a solid state by heat or pressure. Remember, Steno, a traditionalist, still thought that all of this deposition took place during the flood. In the next stage of the discovery of geologic time, natural historians took up the question of whether the Earth has a long or short history.
Catastrophism - maintains that the rocks were deposited in a series of unusual upheavals. This was consistent with the story of the Flood and even after naturalistsbegan to speculate that Noah's Flood may have been only the last in a long sequence of catastrophic changes, remained by default the prevalent mind set.principle of inclusions 2
During the 18th century, the naturalists began to question catastrophism. James Hutton made two significant breakthroughs: He observed that in the modern world, sediments were still being deposited in separate layers by separate depositional events, even without a world-wide deluge. He added two new and powerful principles of stratigraphy to Steno's: If one structure cuts across another, then the one that is being cut must be oldest.
If eroded chunks of one material are incorporated within another, then the eroded material must be older. Hutton had his epiphany at Siccar Point.
Which rocks are younger, the ones above or below? Proposed "Uniformitarianism" in his paper The Theory of the Earth Simply paraphrased, uniformitarianism holds that "The present is the key to the past. This was a momentous and liberating idea because it meant that geologists could reconstruct the history of the Earth by observing processes in the modern world.
They didn't have to invoke catastrophes in which the normal rules don't apply. Alas Hutton was a poor writer or popularizer, so his ideal got little attention until Intellectual successor to James Hutton.
Published Principles of Geology three-volume set, The first geology textbook popularized uniformitarianism. Although modern textbooks treat uniformitarianism as something unambiguusly good, it has it's downsides: The early uniformiatrians went far beyond the philosophy stated above. They also maintained that all geologic processes happened at the same rate in the past as today, and that time was eternal or maybe cyclical.
Hutton claimed that the Earth had, "no vestage of a beginning and no prospect of an end. Probable killer of the giant dinosaurs, for example. The biggest revelation was simply that the Earth had to be millions, not thousands of years old. Scroll to the bottom of this link for and example.
Thus the notion of Geological time was born. Now the problem was how to measure it. There are now two complimentary approaches: In which the order of the origin of various rock units is determined. Absolute or numerical dating: In which an acutal numerical chronologic age is established for rocks.
During the 19th century, however, geologists could only establish the relative ages of rock units. The means to do so had already been provided by Steno and Hutton, but only provided rocks could be seen in direct association.
Principles of Geology
Once again, the study of fossils provided the stimulus for a major innovation: Our understanding of fossils has a varied history: In classical antiquity, scholars knew of and were interested in the bones of ancient animals. The rock layers on the top seem to form a valley but we can tell that Unit I dark blue on one side is the same as the Unit I dark blue on the other side.
There is missing rock in between and a displacement caused by deformation.
Cross-cutting relationships also helps us to understand the timing of events. Younger features cut across older features. Going back to the fault on this image, we know that these rock layers were involved in the fault movement because they are all offset.
We can also determine which beds of rock were tilted and that relationship to the rocks that are not tilted.
Principles of Geology – Time Scavengers
Conglomerate rock containing many smaller pieces. The idea of Components is simple. If you find a rock that has other smaller pieces of rocks within it, the smaller rocks inside must have existed before the larger rock was created. The Principle of Faunal Succession states that a species appears, exists for a time, and then goes extinct.
Time periods are often recognized by the type of fossils you see in them. This is simply the oldest recorded occurrence of a fossil and then the youngest recorded occurrence of a fossil. Rocks that contain fossils occur in a very real and understandable order. Rocks of certain time periods can be recognized and separated by their fossil content Boggs, This is a skill that geologists acquire as they do field work and explore the Earth! The fauna from the Mississippian is very different from the Ordovician and easily distinguishable!
Groups of fossils, or fossil assemblages, can be used to correlate rock units across continents. Relative age dating with fossils is very common and we can use this data to make interpretations about the environment.
Something else that fits into Geologic Principles and basic stratigraphy study of rock layers are unconformities. Unconformities are simply gaps missing data in the rock record, these gaps could indicate a variety of processes.
There are three main types of unconformities: Angular unconformity between the older orange package of rock layers and the younger green package of rock. The curvy line indicates the erosional surface. A disconformity between the older purple sedimentary layers and the younger orange sedimentary layers.