Term
| What are the four foundational ideas of modern geology? |
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Definition
| Absolute (radiometric) dating, relative dating, uniformitarianism, and plate tectonics. |
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Term
| Complete the phrase: “During the middle ages, study of the Earth was limited in the west because _____________.” |
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Definition
| People believed that nature was base and dark. |
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Term
| Explain each of the six principles of relative dating: original horizontality, superposition, lateral continuity, cross- cutting relationships, inclusions, and fossil succession. |
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Definition
| Original horizontality: sedimentary rocks are originally deposited in horizontal layers. Superposition: in an undisturbed sequence of sedimentary rock, older rock units are always found below younger rock units. Lateral continuity: sedimentary rock layers that have been separated by erosion were once continuous. Cross-cutting relationships: a rock unit that is broken must have formed before the break. Inclusions: a material fully enclosed by another material must be older than the enclosing material. Fossil succession: rock units formed during the same period will have the same fossils. |
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Term
| All of the principles of relative dating in the previous question require that the rock layers be in near proximity to each other, with one exception. Which principle is the exception? |
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Definition
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Term
| While working at a coal mine, what did William Smith observe? |
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Definition
| Rock layers can be identified by the unique set of fossils found therein. |
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Term
| How did he interpret these observations? |
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Definition
| Fossils found in sedimentary rock sequences change in a unique, reliable order. |
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Term
| What does the hypothesis of catastrophism suggest about Earth's history? |
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Definition
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Term
| Why was catastrophism proposed in the first place? |
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Definition
| To reconcile observations with the idea of a young Earth. |
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Term
What does the principle of uniformitarianism state? |
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Definition
That Earth's features were formed by the same processes we see
acting today, over a very long period of time. |
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Term
| What does uniformitarianism suggest about the age the Earth? |
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Definition
| That it is very, very old. |
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Term
Does modern geology accept catastrophism, uniformitarianism, both, or neither? |
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Definition
Most features can be explained by
uniformitarianism, though a few are explained by understandable catastrophic events. |
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Term
| Roughly how many pages were in the volume published by James Hutton in 1795? |
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Definition
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Term
How are the eons, eras, and periods in the geologic time scale defined (i.e. what distinguishes, say, the Jurassic
period from the Cretaceous period)?
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Definition
| By the unique set of fossils produced during that time period. |
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Term
| Describe each of the four early attempts at determining the age of the Earth found in the text (Ussher's chronology, Kelvin's cooling estimate, sediment thicknesses, and ocean salinity). In your description, you should include the estimated age of the Earth (if given) and the reason why the method was inaccurate. |
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Definition
| Ussher's chronology (~6,000 years): based on account of creation and genealogical information in the Old Testament; incorrect assumptions and interpretations of what is written. Kelvin's cooling estimate (~10-20 million years): based on known cooling laws; Kelvin did not know that additional heat was being added to the Earth by radioactive decay. Sediment thicknesses (~750 million years): based on extrapolating how much time it would take to deposit sedimentary rocks, based on present day sedimentation rates; sedimentation is not constant, and erosion not taken into account. Ocean salinity (~20 million years): starting with a fresh water ocean, how long does it take to deposit all of the salt, given the present rate at which rivers carry salt to the oceans; salination rates are not constant, and the oceans have maintained a constant salinity for some time. |
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Term
| Describe each of the three accurate macroscopic methods of absolute dating (dendrochronology, varves, and glacial layers). In your description, you should include the relevant time frame of each method (i.e. how far back in time can this method get us?). |
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Definition
| Dendrochronology (~20,000-30,000 years): counting tree rings, including correlating samples from the same area. Varves (~20,000-30,000 years): counting the annual sediment layers at the bottom of glacial lakes. Glacial layers (~800,000 years): counting the annual ice layers in glacial core samples. |
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Term
| Complete the phrase: “decay rates are not significantly altered by ______________ or ___________________.” |
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Definition
| Physical conditions; chemical reactions. |
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Term
| What three things do you need to measure/know in order to accurately use a radioisotope to determine the age of a sample? |
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Definition
| The ratio of parent to daughter atoms at the present day, the half life for the isotope, and the ratio of parent to daughter atoms when the sample first formed. |
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Term
| What is the initial daughter problem? |
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Definition
| We can't always tell exactly how many daughter atoms were present when the rock formed. |
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Term
| Where does 14C come from? |
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Definition
| Neutrons via cosmic radiation collide with nitrogen in the atmosphere, forming 14C. |
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Term
| What is the half life of 14C? |
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Definition
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Term
| Radiocarbon dating can be used to determine ages up to how long ago? |
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Definition
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Term
How are the calibration curves for radiocarbon dating determined? |
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Definition
From organic samples of known age, usually
taken from tree rings or varves. |
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Term
| Uranium-lead dating is only useful for samples older than about ___________________. |
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Definition
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Term
| What is the level of precision in radiometric age measurements today? |
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Definition
| Uncertainties are typically less than 1%. |
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Term
| What causes the changes at the surface of an active planet? |
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Definition
| Erosion, and the constant slow churning of the mantle. |
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Term
What is the estimated temperature of Earth's core? |
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Definition
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Term
Where does Earth's internal heat come from? |
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Definition
From the core (left over heat from when the Earth formed) and the crust
(radioactive decay). |
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Term
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Definition
| Heat seeping through a material. |
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Term
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Definition
The movement of heat due to the rising and falling of material, which is turn is due to the
material's thermal expansion or contraction. |
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Term
What characteristic of a planet is the primary determining factor in how long it will remain active? |
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Definition
Size. Small
planets have a large surface area compared to their volume. Large planets have a small surface area compared to their volume1. The amount of heat a planet holds, initially, is proportional to its volume. The rate at which the heat leaves is proportional to the surface area. Thus, larger planets hold onto their internal heat longer. |
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Term
| Complete the phrase: “Benjamin Franklin even went so far as to suggest that our planet might be much like a ______.” |
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Definition
| Cracked shell floating on a dense fluid. |
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Term
| Complete the phrase: “Wegener additionally realized that if Africa and South America were connected in the past there would be ____________.” |
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Definition
| Similarities in the rocks of the two continents. |
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Term
| Wegener was not a geologist, but rather a __________. |
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Definition
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Term
Complete the phrase: “The biggest problem with Wegener's theory was __________.” |
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Definition
Was a lack of any mechanism
causing the plates to move. |
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Term
| What new technology made it possible to investigate the ocean floor? |
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Definition
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Term
Radiometric dating showed that the age of the ocean floor did what? |
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Definition
Increased as you moved away from mid ocean
ridges. |
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Term
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Definition
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Term
Name and describe the three primary layers of the Earth. |
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Definition
Core (dense center), mantle (dense, solid middle layer),
crust (thin, less dense layer on the very top). |
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Term
Name and describe the three types of plate boundaries. |
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Definition
Convergent (plates are moving toward each other, or
converging), divergent (plates are moving away from each other, or diverging), transform (plates are sliding laterally
past each other). |
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Term
| Most earthquakes and volcanoes are located within about ______ kilometers of a plate boundary. |
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Definition
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Term
| Complete the phrase: “Every place on every continent was once part of a __________.” |
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Definition
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Term
| How long does it take tectonics to dismantle and reassemble supercontinents? |
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Definition
| Hundreds of millions of years. |
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Term
| Annual layers in glaciers. |
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Definition
| Hundreds of thousands of years ago. |
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Term
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Definition
Tens of thousands of years ago.
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Term
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Definition
| tens of thousands of years |
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Term
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Definition
| Tens of thousands of years |
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Term
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Definition
| In excess of tens of millions of years ago. |
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Term
| What form of life dominates throughout most of Earth's history? |
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Definition
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Term
| Complete the phrase: “All forms of change on Earth are _________.” |
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Definition
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Term
Describe how the greenhouse effect works. |
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Definition
Visible light passes through the atmosphere practically unhindered and is
absorbed at the surface. Heat from the surface, on the other hand, attempts to radiate back into space as infrared light.
Greenhouse gasses, while transparent to visible light, are not transparent to the infrared light, thus trapping the heat. |
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Term
Large volcanic events initially cause global _________, but later global _________. (One of these blanks is
“cooling”, the other is “warming”. You need to figure out which word goes in which blank.)
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Definition
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Term
| Oceans cover what percent of the Earth's surface? |
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Definition
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Term
If the Earth were the size of a basketball, what would the volume of the oceans be? |
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Definition
About 8.5 mL, or just under two
teaspoons. |
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Term
What two major things cause changes in sea level? |
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Definition
The size of the ocean basins change (plate tectonics), or the
amount of water in the oceans changes (i.e. the amount of ice over land). |
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Term
How do we know what types of environments existed in various places in the distant past? |
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Definition
It's recorded in the rocks.
Different types of environments produce different physical and chemical signatures in the rocks. |
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Term
| How long ago did the Precambrian start? |
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Definition
| About 4.55 billion years ago. |
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Term
| What percentage of Earth's history takes place in the Precambrian? |
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Definition
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Term
Describe the early atmosphere of Earth, i.e. Identify how much of the various atmospheric gasses (oxygen, nitrogen,
carbon dioxide, etc.) were found in the atmosphere of the early Earth.
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Definition
Lots of methane and carbon dioxide. Very little
or no oxygen. |
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Term
| How long ago did the oceans start to form? |
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Definition
| About 3.8 billion years ago. |
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Term
| How long ago did eukaryotic organisms first appear? |
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Definition
| About 1.5 to 1.9 billion years ago. |
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Term
| How long ago did complex, multicellular life appear? |
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Definition
| About 610 million years ago. |
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Term
| How long ago did organisms with hard parts first appear? |
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Definition
| About 542 million years ago. |
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Term
The Paleozoic era started with “the age of _______”, which was subsequently replaced by the “age of _______”, the
“age of _________”, and ultimately the “age of ____________”.
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Definition
| Invertebrates; fishes; amphibians; reptiles. |
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Term
| How long ago did fossils of land-based plants and animals first appear? |
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Definition
| About 460 million years ago. |
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Term
| When did the Paleozoic era end? |
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Definition
| About 251 million years ago. |
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Term
The Permian extinction saw the demise of ______% of the marine species and _______% of the land species. |
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Definition
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Term
| The Mesozoic era is also called the “age of the _________”. |
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Definition
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Term
How long ago did the Mesozoic era end? How did it happen? |
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Definition
About 65 million years ago, by a cataclysmic meteor
impact. |
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Term
| Some dinosaurs survived the extinction at the end of the Mesozoic era. Today we call them what? |
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Definition
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Term
| The last glacial period of the present ice age ended how long ago? |
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Definition
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Term
| What forms of life characterize(d) the Cenozoic era? |
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Definition
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Term
| How long ago to modern humans first appear? |
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Definition
| Between 130,000 and 190,000 years ago. |
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