ANSWERS TO REVIEW QUESTIONS FOR EXAM 3
Note: These essay-style questions are a supplement to (NOT a subtitute for) lecture notes, handouts, and text reading
2. The oldest known rocks on Earth are 3.8 billion years. From meteorites, which are leftover rocks unchanged from the birth of the solar system, geologists have been able to fix an age of 4.6 billion years.
3. Absolute time is expressed in a definite number or range of years. Relative time does not fix an absolute date; it only establishes a sequence ("which is older or younger, etc.")
4. Uniformitarianism is a concept that stresses the consistency of natural processes over time - in other words, physical laws operated in the distant past on the young Earth as they do today. The popular expression of this is "the present is the key to the past."
5. Uniformitarianism does not imply that the rates of geological processes (i.e. weathering, erosion, mountain building, etc.) are the same today as they were in the past.
6. Faunal succession simply states that once a species of life becomes extinct, it will never reappear in the geologic record. In other words, we will never see dinosaurs alive again.
7. Superposition states that in an undisturbed sequence of sedimentary strata (layered rock), the oldest layers are on the bottom, and the youngest layers are on the top.
8. Radiometric dating involves the measurement of radioisotopes which may occur in old rocks. Parent isotopes such as Uranium eventually decay (their nuclei become smaller, while expelling sub-atomic particles and energy) into stable daughter isotopes. By measuring the relative amounts of parent to daughter elements, the age of the rock may be estimated. Limitations: the rock involved is usually igneous, and the rock must not have re-melted; otherwise the "clock" is reset to the time of melting.
9. Sedimentation rates are not uniform. Lake sediments can take 1000 years to accumulate a millimeter, while storm deposits can pile up yards of thickness in just hours!
It was later determined that the oceans were always salty; so, Joly's assumption that the early ocean was fresh water was invalid.
Lord Kelvin had assumed that the only source of the Earth's heat came from its early formation. He did not know about the heat from radioactive decay (neither did anyone else until later), so his assumption was also wrong.
10. Geologic times units: era, period, epoch
11. Radioactive decay occurs in heavy elements that have an unstable number of neutrons. The neutrons may break apart into alpha particles (which look like helium nuclei), beta particles (energetic electrons), or gamma rays (which are energy waves, not particles).
12. Carbon-14 has a short half life of about 6000 years, and carbon is very common in wood and other organic materials. U-238 has a long half life of 4.5 billion years.
13. Fossils "suddenly" became abundant during the Cambrian Period, about 600 million years ago, because animals evolved hard skeletal parts which allowed their remains to be better preserved. While Cambrian life may not have been more abundant than Precambrian life, it left more and better traces than the former.
14. Factors which can enhance fossil formation:
a. Have a hard skeleton
b. Live and die in water (more sediment available for burial)
c. Be buried quickly after death, preferably in a low oxygen environment (usually a quiet pool of water)
d. Be a member of a large and widespread species
e. Lack of metamorphism over a long geologic time in the area of burial
15. 3 major geologic eras: Paleozoic (Age of Invertebrates), Mesozoic (Age of Reptiles), Cenozoic (Age of Mammals).
16. Cambrian, Ordovician, Silurian, Devonian, Mississippian, Pennsylvanian, Permian, Triassic, Jurassic, Cretaceous, Tertiary, Quaternary. (You should know at least the correct sequence, if not necessarily all of the names).
17. Three sources of heat causing the Great Iron Catastrophe: heat of accretion (coalescence of the earth), angular momentum (mechanical energy from the spinning proto-Earth), and heat from radioactive decay of elements in the Earth's crust. The heat caused the crust to melt at 2000 degrees, and cause the iron and heavy elements to sink to the core, while the less dense material rose to the surface. The original, homogeneous Earth then became a zoned planet.
18. Volcanic eruptions which spew a lot of dust can block sunlight.
19. Two of the earliest life forms: blue green algae and bacteria.
20. Green plants inhale carbon dioxide and exhale oxygen through photosynthesis. They transformed Earth's early anaerobic atmosphere to aerobic (oxygen-rich), which provided enough oxygen in the upper atmosphere to form an ozone layer. This ozone layer filtered out deadly solar ultraviolet rays, which made life on land possible.
21. The 2 major dinosaur groups were: the saurischia (lizard-hipped) and the ornithischia ("bird-hipped).
22. The sea-dwelling contemporaries of the dinosaurs were known as marine reptiles, and the airborne creatures were the flying reptiles.
23. Major dinosaur groups (anatomical), with examples: SAUROPODS (Brontosaurus), CARNOSAURS (Tyrannosaurus), DROMAEOSAURS (Deinonychus), CERATOPSIANS (Triceratops), HADROSAURS (Parasaurolophus), STEGOSAURS (Stegosaurus), ANKYLOSAURS (Ankylosaurus).
24. The Meteorite Impact Theory best explains the great Cretaceous extinction of the dinosaurs and other creatures. Its main evidence consists of: the iridium enrichment of the Cretaceous-Tertiary boundary, shocked quartz grains, and soot deposits indicating a worldwide firestorm.
Four ridiculous dinosaur extinction theories:
a. Mammals ate up the dinosaurs' eggs
b. Dinosaurs died of stupidity
c. Dinosaurs as a race became too old, died of senility
d. Dinosaurs ate poisoned plants
25. The plesiosaur, a long-necked, long-tailed, finned marine reptile, extinct since the Cretaceous, is believed to resemble the descriptions given to the Loch Ness Monster.
25. During the 1600's, European map-makers noticed that the coastline of certain continents seemed to fit together.
26. Alfred Wegener's evidence for Pangaea and continental drift:
a. the apparent "fit" of the continents
b. paleogeographic evidence of fossil tropical plants in cold areas of today
c. similar or closely related fossils found on opposite sides of the Atlantic Ocean (North America and Europe)
d. similar rock types and structures (such as mountains) found on opposite sides of the Atlantic
27. The pattern of magnetic reversals over geologic time was recorded by the ocean floor rock proved that the Atlantic Ocean was no older than 200 million years. Also, it showed that the youngest rock was found near the mid-ocean ridge, while the oldest rock was furthest from the ridge, just off the coast of the continents. In areas such as the Pacific Ocean basin, any rocks older than 200 million years had since been consumed by the subduction zones (trenches).
28. Seafloor spreading is caused by convection currents in the earth's interior, below the lithosphere. At divergent plate boundaries, ocean floor rock is created by basaltic lava which erupts from the interior, which makes the seafloor wider. At convergent plate boundaries, ocean floor rock is destroyed by being subducted by lighter, less dense continental crust; this ocean floor rock is forced down into the trenches and the hot interior of the earth, where it is destroyed. Ocean floor rock is 200 million years older or less, as determined by radiometric dating and interpreting magnetic reversal patterns. Rock of the continents is much older, dating back 3.8 billion years.
29. Subduction is a collision of 2 plates. The heavier, denser (oceanic) plate is subducted by the lighter, less dense (continental) plate. When 2 continental plates collide, they are thrust up into the air to form mountain ranges such as the Himalayas. When 2 oceanic plates collide, an island arc usually results.
30. Oceanic (basaltic) crust, being denser than continental (granitic) crust will always sink down toward the mantle (subducted) when colliding with the latter. This means that no ocean floor rock older than 200 million years will ever be discovered, since this evidence has long been since destroyed by subduction zones (trenches).
31. Magnetite, a magnetic mineral present in mafic rocks such as basalt, orients its slender crystals to the earth's magnetic field while the rock is still molten. When the rock cools below a certain temperature, called the Curie point, it "freezes" the orientation of the earth's magnetic field at the time for the rock's formation. Ancient rocks containing magnetite reveal that the earth's magnetic field has reversed many times. Magnetic reversals can be precisely dated, so it supports plate tectonics.
32. Polar wandering is the apparent change in location of the earth's magnetic North over time. Since there cannot be more than one magnetic pole, it is assumed that the continents drifted over time.
33. The hot spot theory explains the Hawaiian islands. A stationary plume of hot, molten rock originating in the asthenosphere cuts through the crust (which is drifting over time) to form a chain of volcanos.
34. Convection currents in the earth's mantle are believed to be the driving force for plate movements. The circulation of this solid material is believed to take millions of years for just one cycle.
35. The asthenosphere is a soft, "mushy", semi-molten layer of rock located below the lithosphere. It is the origin of magma which erupts at mid-ocean ridges.
36. The earth's crust varies from 10 to 25 miles thick. Oceanic (basaltic) crust is thinner, while continental (granitic) crust is thicker.
37.& 38. Convergent boundary: collision of plates. Example: North American plate and Pacific plate collision produces the Cascade Range of volcanoes.
Divergent boundary: spreading of plates. Example: Mid-Atlantic Ridge (ocean). A land example would be the East African Rift Valley.
Transform fault: fracture zones off-setting mid-ocean ridges.
39. The 3 major types of seismic waves are: 1) P-waves, 2) S-waves, and 3) long or surface waves. P-waves are faster than S-waves; S-waves are faster than surface waves. The lag time between P- and S-waves are used to calculate the distance of a recording station to the earthquake epicenter.
40. The focus is the actual point of the earthquake within the earth's crust; the epicenter is the shortest straight-line path from the focus to the surface.
41. S-waves cannot penetrate liquids. The failure of S-waves to penetrate certain portions of the Earth's interior indicate a liquid iron composition for the outer core (this causes the S-wave "shadow zone"). The abrupt change in composition at the boundary between solid mantle and liquid core also causes P-waves to deflect and change in speed (the P-wave shadow zone).
42. The Richter Scale is a measurement of ground displacement - it is a logarithmic scale whereby one order of magnitude is 10 times greater than the next lower whole number (an "8" is 10 times greater than a "7" and 100 times greater than a "6"). In terms of energy, the Richter scale is 30X higher for each order of magnitude. The Mercalli Scale measures observed damage to man-made structures - this technique is more subjective than the Richter Scale.
43. The New Madrid earthquake, in the New Madrid Fault zone, occurred in 1811-12. The fault zone is deep-seated and cannot be directly observed, so it is poorly understood.
44. Most of the world's earthquakes occur in the Pacific Basin, where Circum-Pacific "Ring of Fire" is located.
45. Earthquake prediction in the West was largely ignored until very recently - even so, it strictly relies on instrumentation, and can only make long-term predictions (on the order of years or decades). Earthquake prediction in the Far East has traditionally heeded the observations of laypersons, and sometimes included information such as abnormal animal behavior.
46. Scientists consider most of the layperson observations of abnormal pre-earthquake animal behavior to be unreliable.
47. A short-term prediction of a major earthquake in Haicheng, China, in 1975, saved thousands of lives.
48. 1) Analysis of layperson eyewitness accounts
2) Recreating geophysical changes observed before earthquakes in the laboratory, and observing the response of animals under controlled conditions.
49. Abnormal animal behavior may be useful as a short-term earthquake prediction technique.
50. 24 hours
Copyright © 1994 by William K. Tong