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the rock record
DETERMINING RELATIVE AGE
| Question | Answer |
|---|---|
| Scottish physician and farmer famous for his ideas and writings about geology | James Hutton (18th Century) |
| a principle that geologic processes that occurred in the past can be explained by current geologic processes | uniformitarianism |
| True or False although the processes of the past and present are the same, the rates of the processes may vary over time. | True (update on Hutton's original principle of uniformitarianism) |
| James Hutton believed that studying the ______ is the key to understanding the past. | present |
| Scientists use to believe that the earth was only _______ years old and that geologic features had formed at the same time. | 6,000 |
| Hutton's principle of uniformitarianism raised serious questions about the _____ of the earth. | age |
| Hutton realized that the geologic formations on his farm must have taken ________ of years to form. | millions |
| the age of an object in relation to the ages of other objects | relative age |
| layers of rocks are called | strata |
| What does relative age indicate about strata (layers of rock) | that one layer is older or younger than another layer |
| What does relative age not indicate about strata (layers of rock) | the exact age of the rock |
| To determine the relative age of rock scientists usually study what type of rocks | sedimentary rocks |
| As the sediments accumulate, they are compressed and become naturally cemented into sedimentary rock layers that are called _____ | beds |
| The boundary between two beds is called a | bedding plane |
| Scientists use a basic principle called _________ to determine the relative age of a layer of sedimentary rock | law of superposition |
| the principle that a sedimentary rock layer is older than the layers above it and younger than the layers below it if the layers are not disturbed is called | law of superposition |
| In the law of superposition a layer on top of another layer is younger or older than the layer below | younger |
| Scientists know that sedimentary rock generally forms in __________ layers | horizontal |
| sedimentary rocks left undisturbed will remain in horizontal layers is called the principle of ______ ____________ | original horizontality |
| Because of principle of original horizontality scientists know that rocks that are not horizontal have been what | tilted or deformed by crustal movements that happened after the layers formed |
| In what case can the law of superposition not be easily applied | when tectonic forces push older layers on top of younger layers or overturn a group of rock layers |
| What is graded bedding | heavy particles settle to the bottom of a lake or river faster than smaller particles which form graded bedding |
| What is a Cross-Bed? | as and slides down the slope of a large sand dune, the sand forms slanting layers |
| What are ripple marks | When waves move back and form on a beach, ripple marks form |
| ripple marks are caused from | waves |
| cross-beds are caused from | sand slides |
| graded bedding is caused from | heavy particles settling down in lake or river |
| When scientists notice that sedimentary rock is not horizontal what are three things they can look for to help determine relative age of rock | 1. graded bedding 2. cross-Beds 2. Ripple marks |
| If larger particles of rocks are found at the top of sedimentary rock what might the scientist think? | layers were probably overturned by tetonic forces |
| In undisturbed sedimentary rock the crests of the ripple marks point _______ | upward |
| what might a scientist think if ripple marks in sedimentary rock is turned downward? | that layers were disturbed by tetonic forces |
| a break in the geologic record created when rock layers are eroded or when sediment is not deposited for a long period of time is called | unconformity |
| An unconformity shows that deposition either stopped for a period of time, or rock may have been removed by erosion before deposition. True or False | True |
| What are the three types of unconformities? | 1. nonconformity 2. angular unconformity 3. disconformity |
| igneous or metamorphic rock uplifted to earth's surace by crustal movements causing boundary between the new sedimentary rock and igneous /metamorphic rock is called | nonconformity |
| rock deposited in horizontal layers folded or tilted and then eroded with a new horizontal layer deposited on top of tilted layer and the bedding planes of older rock are not parallel to those of younger rock deposited above them is called | angular unconformity |
| layers of sediments uplifted without folding or tilting and then eroded. area subsides and deposition resumes. the new layers are deposited horizontally but a large time gap exists where the upper and lower layers meet. this gap is known as | disconformity |
| true or false When rock layers have been disturbed by faults or intrusions, determining relative age is very easy. | false (it can be very difficult) |
| A _____ is a break or crack in the Earth's crust along which rock shifts their position. | fault |
| ________ is mass of igneous rock that forms when magma is injected into rock and then cools and solidifies | intrusion |
| When scientists find faults or intrusions in sedimentary rock what law do they use to determine relative age of rock | the law of crosscutting relationships |
| What is the law of crosscutting relationship | the principle that a fault or body of rock is younger than any other body of rock that it cuts through |
| when there is a fault or intrusion and an unconformity what can scientists tell you about the relative age of the rock | the fault or intrusion is younger than all the rocks it cuts through above and below the unconformity. |
Created by:
kellyaem