Page 563 - 9780077418427.pdf

/Volume/201/MHDQ233/tat78194_disk1of1/0073378194/tat78194_pagefiles
tiL12214_ch21_521-540.indd Page 540 9/23/10 11:10 AM user-f465
tiL12214_ch21_521-540.indd Page 540 9/23/10 11:10 AM user-f465 /Volume/201/MHDQ233/tat78194_disk1of1/0073378194/tat78194_pagefile

Group A—Continued Group B—Continued
10. If the body tissue of an animal contained 100 g of carbon-14 10. If a piece of wood contained 240 g of carbon-14 when the tree
when it died, how many grams of carbon-14 are present in the died, how many grams of carbon-14 are present in the wood if it
tissue if it is 22,920 years old? (Refer to Table 21.2 for the half-life is 28,650 years old? (Refer to Table 21.2 for the half-life of
of carbon-14.) carbon-14.)
11. Analysis of a feldspar crystal in an igneous rock indicated 11. Laboratory analysis of an animal bone buried in bog sediment
12.5 percent of the potassium-40 originally in the crystal was indicated 3.125 percent of the normal proportion of carbon-14 to
present. What is the age of the rock? (Refer to Table 21.2 for the carbon-12. How old is the bog sediment? (Refer to Table 21.2 for
half-life of the potassium-40/argon-40 isotope pair.) the half-life of carbon-14 and to “A Closer Look” in chapter 13
for a discussion of carbon-14 dating.)
12. An earth science class would like to lay out a scale model of the 12. An earth science class would like to lay out a scale model of the
geologic time scale on 90-meter soccer field. Assuming the entire geologic time scale on 90-meter soccer field. Assuming the entire
time of earth history will be represented by the model, what is time of Earth history will be represented by the model, what is
the model dimension for the distance that represents the portion the model dimension for the distance that represents the portion
of time for the Precambrian era? (Use Figure 21.17 to obtain the of time for the Cenozoic era? (Use Figure 21.17 to obtain the age
age of each era.) of each era.)
13. A college class is building a scale model of the geologic time scale 13. A scale model of the geologic time scale is being built on a
on a 28 m basketball court. What is the necessary conversion campus quadrangle that is 400 m long. What is the necessary
ratio for model dimensions in meters per million years (m/Myr) conversion ratio for model dimensions in meters per million
of geologic time? What is the distance at this scale, in meters, years (m/Myr) of geologic time? What is the distance at this scale,
that represents the duration of the Cenozoic era? in meters, that represents the duration of the Jurassic period?
14. A rock layer has a faunal assemblage consisting of a brachiopod 14. A sediment layer has a faunal assemblage consisting of mollusks
with an age range from Late Silurian through Mississippian, with an age range from Paleocene through Miocene, corals with
solitary corals with an age range from Late Ordovician through an age range from Oligocene through Pleistocene, and shark
Middle Devonian, and echinoderms with an age range from the teeth with an age range from the Eocene through the Oligocene.
Early Ordovician through the Early Mississippian. During what During what geologic epoch was this layer deposited?
geologic period was this layer deposited?
15. Two outcrops separated by a distance of 12 km are exposed in a 15. Two outcrops separated by a distance of 32 km are exposed in a
region. The fossils occurring in a region are listed in the region. The fossils occurring in a region are listed in the
following table: following table:

Fossil Age Range Fossil Age Range
A Late Cambrian through Late Devonian A Early Triassic through Cretaceous
B Silurian through Permian B Jurassic through Miocene
C Ordovician through Silurian C Late Jurassic through Cretaceous
D Late Mississippian through Permian D Oligocene through Pliocene
E Mississippian through Early Permian E Pliocene through Pleistocene
Outcrop 1 has a shale layer that contains fossil A overlain by a
Outcrop 1 has a grayish white sandstone layer that contains limestone with fossils B and C. Outcrop 2 has a shale layer that
fossils A and C. Outcrop 2 has a grayish white sandstone layer contains fossil C overlain by a red sandstone with fossils D and E.
that contains fossils B, D, and E. Can the sandstone layer be Which layers can be correlated between outcrops and what is the
correlated between outcrops? age of the layer?

540 CHAPTER 21 Geologic Time 21-20