Anyone who has handled a fossilized
bone knows that it is usually not exactly like
its modern counterpart,
the most obvious difference being that it is often much heavier. Fossils
often have the quality of stone rather than of organic materials, and this has
led
Line
to the use of the term “
petrifaction” (to bring about rock). The implication is that bone,
(5) and other tissues, have somehow been turned into stone, and
this is certainly the explanation given in some texts. But it is
wrong interpretation; fossils are frequently
so dense because the pores and other
spaces in the bone have become filled with minerals taken up from the surrounding
sediments. Some fossil bones have all the interstitial spaces filled with foreign
minerals, including the marrow cavity, if there is
(10) one, while others have taken up but
little from their surroundings. Probably all of the minerals
deposited within the bone have been recrystallized from solution by the action of water percolating thru them. The degree
of mineralization appears to be determined by
the nature of the environment in which the bone was deposited and not by the antiquity of the bone. For example,
the black fossil bones that are so common in many
(15) parts of Florida are heavily
mineralized, but they are only about 20,000 years old, whereas
many of the dinosaur bones from western Canada, which are about 75 million years old, are only partially filled in.
Under optimum conditions the process of mineralization
probably takes thousands rather than millions of years, perhaps considerably less.
(20)
The amount of change that has occurred in fossil bone, even in bone as old
as that of dinosaurs, is often remarkably small. We
are therefore usually able to see the microscopic
structures of the bone, including such fine details as the lacunae where the living
bone cells once resided. The natural bone mineral, the hydroxyapatite, is virtually unaltered too – it has the same
crystal structure as that of modern bone.
(25)
Although nothing remains of the original collagen, some of its component
amino acids are usually still
detectable, together with amino acids of the noncollagen proteins of bone.
21. What does the passage
mainly discuss?
(A) The
location of fossils in North America
(B) The
composition of fossils
(C) Determining
the size and weight of fossils
(D) Procedures
for analyzing fossils
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22. The word “ counterpart”
in line 2 is closest in meaning to
(A) species
(B) version
(C) change
(D)
material
|
23. Why
is fossilized bone heavier than ordinary bone?
(A) Bone
tissue solidifies with age.
(B) The
marrow cavity gradually fills with water
(C) The
organic materials turn to stone
(D) Spaces
within the bone fill with minerals.
24. The
word “ pores” in line 7 is closest in meaning to:
(A) joints
(B) tissues
(C) lines
(D) holes
25. What
can be inferred about a fossil with a high degree of mineralization?
(A) It
was exposed to large amounts of mineral-laden water throughout time.
(B) Mineralization
was complete within one year of the animal’ s death.
(C) Many
colorful crystals can be found in such a fossil.
(D) It
was discovered in western Canada.
26. Which
of the following factors is most important in determining the extent of
mineralization in fossil bones?
(A) The
age of fossil
(B) Environmental
conditions
(C) The
location of the bone in the animal’ s body.
(D) The
type of animal the bone came from
27. Why
does the author compare fossils found in western Canada to those found in
Florida?
(A) To
prove that a fossil’ s age cannot be determined by the amount of mineralization.
(B) To
discuss the large quantity of fossils found in both places
(C) To
suggest that fossils found in both places were the same age.
(D) To
explain why scientists are especially interested in Canadian fossils
28. The
word “ it” in line 24 refers to
(A) hydroxyapatite
(B) microscopic structure
(C) crystal
structure
(D) modern
bone
29. The
word “ detectable” in line 26 is closest in meaning to
(A) sizable
(B) active
(C) moist
(D) apparent
30. Which
of the following does NOT survive in fossils?
(A) Noncollagen
proteins
(B) Hydroxyapatite
(C) Collagen
(D) Amino
acid
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