Rock identification and classification Introduction The study of geology is the study of the Earth, and so is ultimately the study of rocks. Geologists define a rock as: A bound aggregate of minerals, mineraloids, or fragments of other rocks. Typical binding agents are very fine grained minerals e.
Relative dating Cross-cutting relations can be used to determine the relative ages of rock strata and other geological structures.
Methods for relative dating were developed when geology first emerged as a natural science. Geologists still use the following principles today as a means to provide information about geologic history and the Rocks and dates geology analysis of geologic events.
In geology, when an igneous intrusion cuts across a formation of sedimentary rockit can be determined that the igneous intrusion is younger than the sedimentary rock.
Different types of intrusions include stocks, laccolithsbatholithssills and dikes. The principle of cross-cutting relationships pertains to the formation of faults and the age of the sequences through which they cut.
Faults are younger than the rocks they cut; accordingly, if a fault is found that penetrates some formations but not those on top of it, then the formations that were cut are older than the fault, and the ones that are not cut must be younger than the fault.
Finding the key bed in these situations may help determine whether the fault is a normal fault or a thrust fault. For example, in sedimentary rocks, it is common for gravel from an older formation to be ripped up and included in a newer layer.
A similar situation with igneous rocks occurs when xenoliths are found. These foreign bodies are picked up as magma or lava flows, and are incorporated, later to cool in the matrix.
As a result, xenoliths are older than the rock which contains them. The Permian through Jurassic stratigraphy of the Colorado Plateau area of southeastern Utah is an example of both original horizontality and the law of superposition.
These strata make up much of the famous prominent rock formations in widely spaced protected areas such as Capitol Reef National Park and Canyonlands National Park.
From top to bottom: Rounded tan domes of the Navajo Sandstonelayered red Kayenta Formationcliff-forming, vertically jointed, red Wingate Sandstoneslope-forming, purplish Chinle Formationlayered, lighter-red Moenkopi Formationand white, layered Cutler Formation sandstone.
The principle of original horizontality states that the deposition of sediments occurs as essentially horizontal beds. Observation of modern marine and non-marine sediments in a wide variety of environments supports this generalization although cross-bedding is inclined, the overall orientation of cross-bedded units is horizontal.
Logically a younger layer cannot slip beneath a layer previously deposited.
This principle allows sedimentary layers to be viewed as a form of vertical time line, a partial or complete record of the time elapsed from deposition of the lowest layer to deposition of the highest bed.
As organisms exist at the same time period throughout the world, their presence or sometimes absence may be used to provide a relative age of the formations in which they are found.
The principle becomes quite complex, however, given the uncertainties of fossilization, the localization of fossil types due to lateral changes in habitat facies change in sedimentary strataand that not all fossils may be found globally at the same time.
Absolute datingradiometric datingand geochronology Geologists also use methods to determine the absolute age of rock samples and geological events.
These dates are useful on their own and may also be used in conjunction with relative dating methods or to calibrate relative methods.
Rocks and Dates Geology Analysis Words | 5 Pages. The Grand Canyon is a wonderful place to gain a sense of how old the earth really is because of the ability to date the layers of rock in the canyon. Essay on Rocks and Dates Geology Analysis. Essay on Rocks and Dates Geology Analysis. Length: words (3 double-spaced pages) Rating: Strong Essays. Open Document. Essay Preview. The Grand Canyon is a wonderful place to gain a sense of how old the earth really is because of the ability to date the layers of rock in the canyon. The Rocks. Based on the analysis of these samples, scientists estimate that the Earth itself is about billion years old. In addition, the oldest known moon rocks are billion years old. Since the moon and the Earth probably formed at the same time, this supports the current idea of the Earth's age.
This changed the understanding of geologic time. Previously, geologists could only use fossils and stratigraphic correlation to date sections of rock relative to one another. With isotopic dates, it became possible to assign absolute ages to rock units, and these absolute dates could be applied to fossil sequences in which there was datable material, converting the old relative ages into new absolute ages.
For many geologic applications, isotope ratios of radioactive elements are measured in minerals that give the amount of time that has passed since a rock passed through its particular closure temperaturethe point at which different radiometric isotopes stop diffusing into and out of the crystal lattice.
Common methods include uranium-lead datingpotassium-argon datingargon-argon dating and uranium-thorium dating. These methods are used for a variety of applications.You can use our interactive to help you identify an actual rock, or, if you don't have a sample, you can use one of our virtual rocks.
Tips to help you identify rocks Geology toolkit: what rock is that? What biological clocks and geological rocks tell us about life in space No such scepticism haunts the much more well-established palaeomagnetic dates used in geology.
Our analysis compared. Rocks and Dates Geology Analysis Words | 5 Pages. The Grand Canyon is a wonderful place to gain a sense of how old the earth really is because of the ability to date the layers of rock in the canyon. grand canyon, rock layers, geology - Rocks and Dates Geology Analysis.
Rock identification and classification Introduction. The study of geology is the study of the Earth, and so is ultimately the study of rocks. In depth analysis of rocks using a microscope or sophisticated analytical laboratory equipment provides important information on their composition.
Major Concepts •Foldsin rocks range from microscopic to hundreds of kilometers across. • Faults are fractures along which displacement has occurred.