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Topic 13:Geol.Hist A
Pages (278-287) Relative Dating
| Question | Answer |
|---|---|
| Define the term, rock strata: | Layers of rock that yield Earth's 4.6 Billion year history to a geologist. |
| List four aspects of rock strata that geologists consider to better understand Earth's history. | Rock composition, structure, position, and fossil content are key ! |
| Explain "relative dating" of rock strata or geologic events. | Organization of "older than" or "younger than"; but no exact dating. |
| Define "absolute dating": | Using methods that permit a more specific age of an event to a specific time span by using radiometric dating or index fossils. |
| Describe the principle of superposition. | If undisturbed, rock strata on the bottom are oldest, while strata above are younger. |
| Discuss "cross cutting" relationships. | Rock strata must be older than the events that effect them. Thus, the rock must be older than the fault that splits them, or the contact metamorphism that recrystallizes the rock. |
| Which is older, the clastic rock fragments or the sedimentary rock formed through compaction and cementation of these sediments? | The rock fragments are older as the sedimentary rock would not exist without the particles. |
| Compare an intrusion with an extrusion. | An intrusion contact metamorphoses on both sides of the crack through which the magma squeezes and the igneous rock is intrusive. An extrusion breaks earth's surface, contact metamorphoses only below, and is extrusive. |
| Describe a vein. | A mineral deposit that was created as a watery solution squeezed its way through rock. We often refer to a vein of gold or silver. |
| Contrast a fault with a joint. | A fault has enjoyed movement while a joint is a stationary crack in rock. |
| Explain correlation. | To correlate is to compare and better understand a relationship via clues and methods. |
| Discuss rock strata correlation. | Comparing two outcrops to better understand the relative dating of strata, & possible prior relationships such as common rock formation sequence suggesting that the strata were once connected. |
| Define an index fossil: | Evidences of past life found in sedimentary rocks which were both short lived and wide spread! Humans are perfect index fossils as we have only existed for two million years and live all around the world. |
| How can volcanic ash be used to date rock strata? | Volcanic ash is like a finger print with unique chemical properties. Anywhere that the ash is found, we know that this was the surface of Earth at the time of eruption this providing a common time marker. |
| Where in the ESRT is there a Table of Index Fossils for reference purposes? | Page 8 & 9, Geologic History, along the bottom of the pages. Match up letters with the columns found on page 9 to see when species emerged, or became extinct! |
| What percentage of time does the Pre Cambrian Eon make up? (pg 284) | 88% !! |
| List the three Eras that make up the Phanerozoic Eon. | Paleozoic, Mesozoic, and Cenozoic Eras. |
| Describe an unconformity. | A missing layer of rock due to uplift, weathering and erosion. Evidence of the strata is missing but may be observed in other related rock formations. |
| Define orogeny: | Mountain building periods. Name the four major periods in the geologic history of New York!! (see page 9, ESRT) |
| Can you complete all multiple choice questions in Topic 13, numbers (1 - 36)? | Please do it now, after you have read and outlined the sections found in Topic 13! |
Created by:
whearn
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