from The Textbook Letter, March-April 1996

Reviewing a middle-school book in earth science

Merrill Earth Science
1995. 744 pages. ISBN of the student's edition: 0-02-826908-X.
Glencoe/McGraw-Hill, 936 Eastwind Drive, Westerville, Ohio 43081.
(Glencoe/McGraw-Hill is a part of McGraw-Hill, Inc.)

The More I See It,
the Less I Like It

Peter U. Rodda

When I reviewed the 1993 version of Glencoe's Merrill Earth Science, I concluded that it was the best middle-school earth-science textbook that I had seen, but that it could be made better. I also said that it really was two books, poorly integrated, that had been bound in the same set of covers. One was a book about earth science, the other a book about environmental problems.

Looking at the 1995 version, I find that all of those statements still apply. The content of Merrill Earth Science is virtually unchanged, and the book still looks the same -- notwithstanding that the pages are a little more cluttered with sidebars, and a few photographs have been altered. On page 374, for example, a picture of some damage caused by the Loma Prieta earthquake (in 1989) has been replaced by a picture of damage caused by the Northridge earthquake (in 1994). This is just window dressing.

The only significant change that I have detected in the 1995 version involves the "Activity" pages. Many of the activities have been rewritten, redesigned or retitled, and some have been replaced. Sadly, however, there still is no activity that will take the student outside the classroom to look at Earth.

In inspecting the 1995 version I have checked to see whether Glencoe's writers, editors and illustrators have corrected the specific errors and other defects that I saw in the 1993 book. What I have found has left me disappointed.

In chapter 1 the writers continue to confuse "science," meaning a way of thinking about nature, with various scientific disciplines (such as physics or chemistry) and even with technology. Students will be better off if they skip this chapter.

Unit 2, called "Rocks and Minerals," is still plagued by confusion about the definition of mineral. In the 1993 version a mineral was any naturally occurring solid, with a definite structure and composition, that was not a product of any living thing. The 1995 book repeats that definition but then adds this:

Coal is made of carbon from living things. Although geologists do not classify coal as a mineral, some people do. Miners, for example, generally classify anything taken from the ground that has commercial value as a "mineral resource." This includes organic materials such as coal and petroleum.

This grudging concession that "miners" (but no other people, apparently) use a broad definition of mineral does not make much difference because it has not been carried into the rest of the unit. The rest of the unit retains the old confusions and illogical assertions that arise from defining mineral too narrowly, and even the section that is specifically devoted to mineral resources doesn't reflect the broader definition. Nothing in that section has been changed, and the only resources that are mentioned are gems and metallic ores. Both coal and petroleum are ignored, as are natural gas, limestone and many other important mineral resources.

Later in the unit, there is an expanded definition of rock. In the 1993 book a rock was "a mixture of minerals," but now it is "a mixture of minerals, mineraloids, glass, or organic matter." I suppose that mineraloid means mineral-like, but it isn't defined in this book and doesn't appear in any of my dictionaries. Whatever mineraloid may mean, the new definition of rock has the virtue of encompassing such materials as obsidian, pumice, coal and limestone, none of which were covered by the 1993 definition.

The ways in which earth-science books use the terms mineral and rock create misconceptions and needless contradictions, as I've explained in earlier reviews. The problem is that the textbook-writers have uncritically adopted the restricted definition of mineral used in mineralogy, and they have insisted on using that definition in situations where it simply doesn't apply. Some mineralogy textbooks acknowledge that the mineralogical definition is a restricted one, developed for special purposes. Why do the writers of introductory earth-science books continue to pretend that it is a general definition, and why do they continue to force it onto young students? I suggest that they use this definition instead: A mineral is any substance that occurs naturally in the earth and is essentially uniform in its properties and composition. I also recommend that rock be defined in a straightforward way: A rock is an aggregate of solid minerals.

Another uncorrected deficiency in the "Rocks and Minerals" unit is the lack of attention to the dozen common minerals that make up most of Earth's crust.

In unit 3, titled "The Changing Surface of Earth," the discussions of erosion and deposition are still superficial, and the writers still fail to acknowledge the different uses of the word soil.

In unit 5, "Earth's Internal Processes," the section on earthquakes still lacks, and still needs, a seismic-risk map of the United States. A small improvement can be seen in the chapter about volcanoes, which no longer claims that "volcanoes in rift zones like Iceland" are shield volcanoes. But the chapter still ignores fissure eruptions, and the material about batholiths and other igneous intrusions is still misplaced.

Persistent Confusion

Unit 6, "Change and Earth History" is still confused in its arrangement of major topics. In the section called "Absolute Ages of Rocks," a new paragraph tells that radiometric dating is applied principally to igneous rocks and metamorphic rocks. This is a useful correction. (The 1993 book gave the impression that almost any rock could be dated radiometrically.) Unfortunately, the section still fails to tell what radiometric dating really is, or how it is performed. What does a scientist actually do to determine a rock's age? The book doesn't say.

Equally disappointing is the retention of the misleading claim that "Before radiometric dating was available, many people had estimated the age of Earth to be only a few thousand years old [sic]." That is unacceptable for two reasons. First, the people who believed that Earth was "only a few thousand years old" had derived that belief from biblical lore -- they had not "estimated" the age of Earth in any scientific way. And the fact that Earth's age is much greater than "a few thousand years" was established, scientifically, long before the development of radiometric dating.

Unit 7, "Earth's Resources," is virtually the same as it was before, and it represents the culmination of the environmentalism that runs throughout Merrill Earth Science. Despite its title, this unit doesn't say much about earth's resources. It focuses on environmental problems (viewed in a socio-political context), and the material is only weakly tied to the earth sciences.

The more I look at this badly integrated combination of science and environmentalism, the less I like it. The environmentalism is mostly negative, and the whole book short-changes its readers by failing to explain the roles that resources play in industrialized societies. Overall, it seems to emphasize environmental abuses, and seems to promote a sort of environmental activism, instead of helping students to learn the science that would enable them to understand environmental matters.

Peter U. Rodda, a geologist and paleontologist, is a staff scientist at the California Academy of Sciences, in San Francisco. His research focuses on fossil mollusks from the Cretaceous Period and more recent times.


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