Dating Sedimentary Rock - How Do Scientists Determine the Age of Dinosaur Bones? | HowStuffWorks
This activity on determining age of rocks and fossils is intended for 8th or 9th grade Explore this link for additional information on the topics covered in this lesson: 5) To use radiometric dating and the principles of determining relative age to Principle of superposition: Younger sedimentary rocks are deposited on top of. But carbon dating won't work on dinosaur bones. Fossils, however, form in sedimentary rock -- sediment quickly covers a dinosaur's body, and the. In order for sedimentary rock to form, the following processes must happen: To retake the quiz, reload the page and then select "no" when the "Resume Quiz".
As such, they were considered unlikely to recur on what was thought to be an unchanging world. With the exception of a few prescient individuals such as Roger Bacon c. He recognized that the marine organisms now found as fossils in rocks exposed in the Tuscan Hills were simply ancient animals that lived in the region when it had been covered by the sea and were eventually buried by muds along the seafloor.
He also recognized that the rivers of northern Italy, flowing south from the Alps and emptying into the sea, had done so for a very long time. In spite of this deductive approach to interpreting natural events and the possibility that they might be preserved and later observed as part of a rock outcropping, little or no attention was given to the history—namely, the sequence of events in their natural progression—that might be preserved in these same rocks.
Following from this observation, Steno concluded that the Tuscan rocks demonstrated superpositional relationships: This is the crux of what is now known as the principle of superposition.
Steno put forth still another idea—that layered rocks were likely to be deposited horizontally. Steno, NicolausNicolaus Steno, engraving, Steno's four laws of stratigraphy. The early English geologist John Stracheyfor example, produced in what may well have been the first modern geologic maps of rock strata. He also described the succession of strata associated with coal-bearing sedimentary rocks in Somersetshire, the same region of England where he had mapped the rock exposures.
Classification of stratified rocks In Johann Gottlob Lehmann of Germany reported on the succession of rocks in the southern part of his country and the Alps, measuring and describing their compositional and spatial variation. In Italy, again in the Tuscan Hills in the vicinity of Florence, Giovanni Arduinoregarded by many as the father of Italian geology, proposed a four-component rock succession.
sedimentary rock | Definition, Formation, Examples, & Facts | y3y3games.info
In addition, Arduino proposed another category, the Tertiary division, to account for poorly consolidated though stratified fossil-bearing rocks that were superpositionally older than the overlying alluvium but distinct and separate from the hard underlying stratified rocks of the Secondary.
These rock bodies would constitute formations in modern terminology. Nearly 1, kilometres miles to the east, the German naturalist Peter Simon Pallas was studying rock sequences exposed in the southern Urals of eastern Russia.
Thus, by the latter part of the 18th century, the superpositional concept of rock strata had been firmly established through a number of independent investigations throughout Europe. Were the various layers at each site similar to those of other sites?
Sedimentary Rocks Formation and Fossils!
In short, was correlation among these various sites now possible? The emergence of modern geologic thought Inherent in many of the assumptions underlying the early attempts at interpreting natural phenomena in the latter part of the 18th century was the ongoing controversy between the biblical view of Earth processes and history and a more direct approach based on what could be observed and understood from various physical relationships demonstrable in nature.
A substantial amount of information about the compositional character of many rock sequences was beginning to accumulate at this time. Thus arose an increasingly vocal challenge to the Neptunist theory.
Perhaps the quintessential spokesman for the application of the scientific method in solving problems presented in the complex world of natural history, Hutton took issue with the catastrophist and Neptunist approach to interpreting rock histories and instead used deductive reasoning to explain what he saw.
The rocks of the Scottish coast and the area around Edinburgh proved the catalyst for his argument that the Earth is indeed a dynamic, ever-changing system, subject to a sequence of recurrent cycles of erosion and deposition and of subsidence and uplift. Courtesy of Lord Bruntisfield; photograph, J. It was not easy for Hutton to popularize his ideas, however. Nonetheless, another 30 years were to pass before Neptunist and catastrophist views of Earth history were finally replaced by those grounded in a uniformitarian approach.
Also, it was becoming increasingly difficult to accept certain assertions of Werner that some rock types e. It was this latter observation that finally rendered the Neptunist theory unsustainable.
Hutton observed that basaltic rocks exposed in the Salisbury Craigsjust on the outskirts of Edinburgh, seemed to have baked adjacent enclosing sediments lying both below and above the basalt. This simple observation indicated that the basalt was emplaced within the sedimentary succession while it was still sufficiently hot to have altered the sedimentary material.
Clearly, basalt could not form in this way as a precipitate from the primordial ocean as Werner had claimed. While explaining that basalt may be intrusive, the Salisbury Craigs observations did not fully satisfy the argument that some basalts are not intrusive.
Perhaps the Neptunist approach had some validity? The resolution of this latter problem occurred at an area of recent volcanism in the Auvergne area of central France.
Lyell, however, imposed some conditions on uniformitarianism that perhaps had not been intended by Hutton: No accommodation was made for past conditions that do not have modern counterparts.
In short, volcanic eruptions, earthquakes, and other violent geologic events may indeed have occurred earlier in Earth history but no more frequently nor with greater intensity than today; accordingly, the surface features of the Earth are altered very gradually by a series of small changes rather than by occasional cataclysmic phenomena.
This, along with the increased recognition of the utility of fossils in interpreting rock successions, made it possible to begin addressing the question of the meaning of time in Earth history.
Determining the relationships of fossils with rock strata The hypothesis of fossil succession in the work of Georges Cuvier During this period of confrontation between the proponents of Neptunism and uniformitarianism, there emerged evidence resulting from a lengthy and detailed study of the fossiliferous strata of the Paris Basin that rock successions were not necessarily complete records of past geologic events.
In fact, significant breaks frequently occur in the superpositional record. These breaks affect not only the lithologic character of the succession but also the character of the fossils found in the various strata. Indeed, they seemed to represent extinct forms, which, when viewed in the context of the succession of strata with which they were associated, constituted part of a record of biological succession punctuated by numerous extinctions.
Sedimentary Rocks Lesson #13
These, in turn, were followed by a seeming renewal of more advanced but related forms and were separated from each other by breaks in the associated rock record. Whatever the actual cause, Cuvier felt that the evidence provided by the record of faunal succession in the Paris Basin could be interpreted by invoking recurring catastrophic geologic events, which in turn contributed to recurring massive faunal extinction, followed at a later time by biological renewal.
In the course of evaluating various natural rock outcroppings, quarries, canals, and mines during the early s, Smith increasingly utilized the fossil content as well as the lithologic character of various rock strata to identify the successional position of different rocks, and he made use of this information to effect a correlation among various localities he had studied. The consistency of the relationships that Smith observed eventually led him to conclude that there is indeed faunal succession and that there appears to be a consistent progression of forms from more primitive to more advanced.
As a result of this observation, Smith was able to begin what was to amount to a monumental effort at synthesizing all that was then known of the rock successions outcropping throughout parts of Great Britain.Introduction to Sedimentary Rocks
With this, it now became possible to assume within a reasonable degree of certainty that correlation could be made between and among widely separated areas.
How do you study it? How can you make any conclusions about rock layers that make such a crazy arrangement? Geologists establish the age of rocks in two ways: Numerical dating determines the actual ages of rocks through the study of radioactive decay.
Relative dating cannot establish absolute age, but it can establish whether one rock is older or younger than another. Relative dating requires an extensive knowledge of stratigraphic succession, a fancy term for the way rock strata are built up and changed by geologic processes.
In this lesson, we'll learn a few basic principles of stratigraphic succession and see whether we can find relative dates for those strange strata we found in the Grand Canyon. Original Horizontality In order to establish relative dates, geologists must make an initial assumption about the way rock strata are formed. It's called the Principle of Original Horizontality, and it just means what it sounds like: Of course, it only applies to sedimentary rocks. Recall that sedimentary rock is composed of