| Term | Definition |
|---|
| Relative Dating | The use of law of superposition, the principle of original horizontality, and the principle of cross-cutting to hlep geologists determine the sequence in which events occurred, but not how long ago they occurend |
| Uniformitarianism | states that the physical , chemical, and biological laws that operate today have also operated in the geologic past |
| In studying Earth's history, geologists make use of three main ideas... | 1. The rock record provides evidence of geological events and life forms of the past. 2. Processes observed on Earth in the present also acted in the past. 3. Earth is very old and has changed over geologic time |
| Law of superposition | in and undeformed sequence of sedimentary rocks, each layer is older than the one avoce it and younger than the one below it, The geologic principle that states that in horizontal layers of sedimentary rock, each layer is older than the layer above it and younger than the layer below it. |
| Principle of Original horizontality | Layers of sediment are generally deposited in a horizontal position. Thus, if we observe rock layers that are flat, it means they have not been disturbed. If they are folded or inclined at a steep angle they must have moved into that position by disturbances |
| Principle of Cross-cutting relationships | When a fault cut through rock layers,or when magma intrudes other rocks and hardens, then the fault or intrusion is younger than the rocks around it |
| How to read the rock record | Methods that geologists use to interpret the rock record include the study of inclusions and unconformities. They also correlate rock layers at different locations |
| Inclusions | Inclusions are pieces of one rock unit that are contained within another. The rock unit next to the one containing the inclusion must have been there first in order to provide the rock fragments |
| Unconformities | a break in the geologic record created when rock layers are eroded or when sediment is not deposited for a long period of time. |
| Correlating rock layers | Geologists use correlation to match rocks of similar age in different locations. Geologists often correlate layers by noting the position of a distinctive rock layer in a sequence of layers |
| Types of Fossils | The diff. types of fossils are petrified fossils, molds and casts, carbon films, preserved remains, trace fossils |
| petrified fossils | mineral-rich water soaks into the small cavities and pours of the original organism. the minerals precipitate from the water and fill the spaces. the petrified food is formed the same way |
| molds and casts | when a shell or structure is buried in sediment and then dissolved by underground water |
| carbon film | preserved details and leaves within the carbon from an object/animal getting caught in it and overtime liquids and gases are squeezed out producing the carbon films |
| trace fossils | animal footprint/other object preserved in sediment |
| preserved remains | A part of an organism/whole organism which is preserved/frozen in sticky resin |
| Conditions for Fossilization | Two conditions that are favorable for fossilization are rapid burial and possession of hard parts |
| Fossil Succession | Fossil organisms succeed each other in a definite and determined oder |
| Theory of Evolution | Life forms have changed over time and have changed from simpler to more complex forms |
| Natural selection | individuals that are better adapt to environment are more likely to reproduce than others of the same type |
| Fossils and Correlation | Fossils are used within the rock record to determine the age of rocks and reconstruct past environments |
| index fossil | A fossil that only lived during a limited span of time and is geographically wide spread and abundant in the fossil record |
| Radioactivity | During radioactive decay, unstable atomic nuclei spontaneously decay releasing energy |
| Radioactive isotopes | Diff. forms of an element that have diff. number of neutrons, trying to break down in order to become stable |
| Half-Life | Time necessary for one half of a nuclei in a sample to decay into stable isotope |
| Radiometric Dating | Scientists measure the ratio between the radioactive parent isotope and the daughter products in a sample to be dated. The older the sample the more daughters there are. |
| Dating with Carbon-14 | Organic material substance that contains carbon and comes from a living thing. carbon-13 is the radioactive isotope of carbon. carbon 14 is continuously produced in the upper atmosphere |
| Structure of the Time scale | Eons represent the longest intervals of geologic time. eons are divided in ear. each era is subdivided into periods. finally, periods are divided into still smaller units called epochs. |
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