The term “fossil” often implies petrifaction, literally a transformation
into stone. After the death of an organism,
the soft tissue is ordinarily consumed by scavengers and bacteria.
They empty shell of a snail
or clam may be left behind, and if it is sufficiently durable and resistant
to dissolution, it may remain basically unchanged for a long period of time.
Indeed, unaltered shells of marine invertebrates are known from deposits over
100 million years old. In many marine creatures,
however, the skeleton is composed of mineral variety of calcium carbonate
called "aragonite".
Although aragonite has the same composition as the more familiar mineral
known as calcite, it has a different crystal form, is relatively unstable,
and in time changes to the more stable calcite.
Q5 Why does the author mention “aragonite” in the passage?
○To emphasize that some fossils remain unaltered for millions of years.
○To contrast fossil formation in organisms with soft tissue and in
organisms with hard shells
○To explain that some marine organisms must undergo chemical changes
in order to fossilize
○To explain why fossil shells are more likely to
survive than are fossil skeletons.
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為何A不對THX
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