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fossils & rock rec
fossils and the rock record
| Question | Answer |
|---|---|
| geologic time scale | a record of earth's history from it's origin 4.6 billions years ago to the present. |
| geologic eras | Cenozoic ( 65 million. age of mammals), mesozoic ( 225 million. age of reptiles), Paleozoic ( 560 million. age of invertebrates) , precambrian ( 4.6 billion. bacteria formed in oceans) |
| eon | the longest time unit and is measured in billions of years. |
| era | the next longest span of time; it is measured in hundreds of millions to billions of years. |
| period | the life forms that were abundant or became extinct during the time in which specific rocks were deposited. millions of tens of years. |
| epoch | even smaller divisions of geologic time |
| uniformitarianism | the processes occurring today have been occurring since the earth formed- James Hutton ( ex mountain building, erosion and earthquakes) |
| relative dating | places events in a sequence but doesn't identify the exact date of occurrence |
| superposition ( original horizontality) | in a sequence of undisturbed sedimentary rocks, any rock layer that rests on top of another is younger than the rock below it. oldest bottom, newest- top |
| cross cutting relationships | any rock unit that crosses the boundaries of another is younger than the rock body it cuts across. |
| intrusion | magma that moves through a rock ( fracture) |
| fault | break in a rock along which movements occurs; this is shown by a line where layers are displaced |
| inclusion principle | any rock found included in another, is older than the rock around it. ex. pebbles in a conglomerate. |
| correlation | matching of out crops of rock from one geographic region to another. - same rock layers at different locations matched by distinct fossils or unique minerals. |
| law of deformation | a rock cannot change until after it has formed |
| fold | a rock layer that is bent due to pressure. bent up- anticline. downwards- syncline |
| unconformity | a missing rock layer that represents missing time. this is shown by a black wavy line. |
| angular unconformity | the gap in the rock record that occurs between folded or uplifted rock layers and a sedimentary rock layer on top of them. |
| absolute age | allows you to determine the actual age of a rock, fossil or other object. |
| radioactive decay | the emission of radioactive particles and the resulting change into other elements over time. constant rate of how decays into something else. |
| radiometric dating | determining the ratio of parent nuclei to daughter nuclei within a given rock or fossil; gives the absolute age. |
| half life | time it takes for 1/2 of the original amount of material to decay. 5730 years |
| carbon 14 | used to date material of organic origin; good up to 75,000 years ( ex. amber, human bones, charcoal) |
| uranium 238 | decays into Pb- 206 at a constant rate used for dating things older than 500,000 years |
| parent element | original element |
| daughter element | new element after decay |
| dendrochronology | the science of comparing annual growth rings in tress to date events in the past. |
| varve | bands of alternating light and dark colored, sentiment. - similar to tree rings to track tree climate change. |
| keybed | when a layer is formed by an instantaneous or short lived event; a time marker. ex. volcanic eruption deposit ) mt st Helens) |
| fossil | evidence or remains of once living plants or animals. most are extinct. |
| evolution | change in population as a result of environmental changes. |
| original preservation | - la brea tar pits - amber insects - mummified ( dried out) - freezing - both hard and soft parts very uncommon for complete to remaiun exist |
| replaced remains ( altered hard parts) | - molds and casts, hollowed out impressions - perminerallization- process by which pore spaces are filled in with mineral material - organic material is gone - |
| index fossil | must be easily recognized -abundant - must be widely distributed geographically - short lived- - used for correlation. |
| importance of studying fossils | earth's history. shows evolution. gas and oil |
| trace fossil | foot prints - coprolites ( poop) egg shells |
| formation of fossils | quick burial - hard parts - lots of time |
| information provided for fossils | - studies microfossils to look for gas and oil - allows scientists interpret earth's history - evidence of ancient climates and environments - shows changes in life forms over time |
| age of earth | - 4.1 - 4.6 billion |
| evidence of age of earth | must be atleast as old as oldest rocks ( 4.1 to 4.2 billions) based on zircon minerals in rocks - meteorites on earth have been dated to 4.5 to 4.7 billion - oldest moon rocks collected by Apollo missions 4.6 billion |
| 3 sources of earth's early heat | - radioactive decay - most of earth's current internal heat - impacts of meteorites and asteroids- lots of impact during early solar system. - gravitational contraction- meteorites increased size of earth causing underlying layers to contract- |
| formation of earths crust | - when earth formed dense elements like iron and nickel concentrated in the core. - low density elements and minerals rose to surface of magma. - differentiation |
| differentiation | process by which a planet becomes internally zoned- heavy materials sink, light rise |
| Precambrian shield | continents contain a core of Archean and Proterozoic rocks ( original rock) |
| Canadian shield | the name of the precambrian shield in north America |
| outgassing | |
| formation of earth's atmosphere | low on oxygen - low on ozone to block uv light - lots of hydrogen |
| cyanobacteria | 3.5 billion year old bacteria with chlorophyll |
| stromatolites | large mats and mounds of cyanobacteria |
| red beds | sedimentary rocks that are younger than 1.8 billion years |
| formation of oceans | -formed from water vapor outgassing from volcanoes - water vapor cooled and formed liquid water - water dissolving minerals make oceans salty |
| controversial hypothesis about formation of oceans | |
| miller urey experiment | |
| environment in which scientists believe life began | |
| banded iron formation | deposit of alternating bands of rock and iron oxide. |
Created by:
dk7
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