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AAAS  :: Project 2061  :: Textbook Evaluations

Middle Grades Science Textbooks: A Benchmarks-Based Evaluation

Glencoe Earth Science, Life Science, and Physical Science. Glencoe/McGraw-Hill, 1997
Earth Science Life Science Physical Science

About this Evaluation Report
Content Analysis
Instructional Analysis

[Explanation] This section examines whether the curriculum material's content aligns with the specific key ideas that have been selected for use in the analysis.
[Explanation] This section examines whether the curriculum material develops an evidence-based argument in support of the key ideas, including whether the case presented is valid, comprehensible, and convincing.
[Explanation] This section examines whether the curriculum material makes connections (1) among the key ideas, (2) between the key ideas and their prerequisites, and (3) between the key ideas and other, related ideas.
[Explanation] This section notes whether the curriculum material presents any information that is more advanced than the set of key ideas, looking particularly at whether the “beyond literacy” information interrupts the presentation of the grade-appropriate information.
[Explanation] This section notes whether the curriculum material presents any information that contains errors, misleading statements, or statements that may reinforce commonly held student misconceptions.


Idea a: The surface of the Earth is changing continually.
There is a content match. In several places the text asserts the general statement that the Earth is changing or has changed over time (pp. 117s, 171s, 187s, 222-226s). Many of these statements focus on how the Earth's surface has changed in the past. Some statements imply ongoing change, as in the following sentence included in a photograph caption: "The size and shape of these islands constantly change due to wave action" (p. 226s). In this case, however, neither the photograph nor this explanation is likely to help students understand the change. In Chapter 11: Plate Tectonics, however, a few assertions or questions imply that the Earth continues to change, such as in,  "[w]hat will happen to the Atlantic Ocean during the next 100 million years?" (p. 297s, Figure 11-4). Very few activities have students investigate the constancy of change on the Earth's surface. However, one activity does ask students to research the altering boundary between Mexico and the United States caused by the changing course of the Rio Grande (p. 209t).

Idea b: Several processes contribute to changing the Earth’s surface.

There is a content match. Many chapters address several Earth-changing processes specifically. For instance, Chapter 7: Erosional Forces covers slumps, creep, rockslides, mudflows, land development, continental glaciers, valley glaciers, wind erosion, and sand dune migration in considerable detail, and other chapters also present relevant content. However, the focus throughout is on how the individual processes work, rather than on how they change the Earth’s surface. Furthermore, the idea that multiple processes work together or at the same time to change the Earth’s surface is not developed. For example, although the erosional forces that wear down mountains are discussed in Chapter 6: Weathering and Soil (see p. 148s), and faulting and mountain-building processes are addressed in Chapter 9: Earthquakes (see pp. 238–239s), the idea that mountains can be built up at the same time that they are being worn down is not addressed. There are many activities that have students examine the processes that change the Earth, such as the effect of wind on sediments (pp. 192–193s), mass movements (p. 176s), and glacial grooving (p. 186s). Furthermore, many review questions focus on how individual processes work, such as how a glacier causes erosion (p. 187s), but very few ask how an individual process changes the surface of the Earth. One question asks students to compare and contrast abrasion and deflation and how they affect the surface of the Earth (p. 195s).

Idea c: The processes that shape the Earth today are similar to the processes that shaped the Earth in the past.

There is a content match. This idea is described briefly in one paragraph (p. 347s), but it is not related to any of the specific processes that change the Earth, such as those mentioned in earlier chapters. Very few questions focus on this idea. For example, students are asked why James Hutton and others inferred that the Earth had to be much older than a few thousand years (p. 352s). The material does not appear to include any activities that address this idea.

Idea d: Some of the processes are abrupt, such as earthquakes and volcanic eruptions, while some are slow, such as the movement of continents and erosion.

There is a content match. The material presents both abrupt and slow changes to the Earth's surface. For example, time-sequence photographs show the first 53 seconds of the Mount Saint Helens eruption (pp. 276-277s). Unfortunately, the ultimate changes to the Earth's surface in these photographs are hidden by the ash flow, and there is no photograph of the mountain and its surrounding area showing how they looked after the eruption. Other abrupt changes are mentioned in the student text but without photographs. For example, Figure 9-6 diagrams an earthquake (p. 244s). As the caption explains, "Sudden movement along a fault releases energy that causes an earthquake" (p. 244s). Slow processes such as weathering and tectonic motion are mentioned in the text, too. For example, the probable locations of the continents are shown at 250 million years ago, 180 million years ago, and their present locations (p. 297s). No questions or activities address this idea.

Idea e: Slow but continuous processes can, over very long times, cause significant changes on the Earth’s surface.

There is not a content match. The idea of significant change occurring over long time spans is implicit in the material's discussions of the processes of mountain building, weathering, and tectonic plate motion. However, the material does not explain that such change results from small unnoticeable changes that accumulate over long times. For example, the caption for a diagram of mountains eroding from weathering states only that, "Over long periods of time, weathering helps change sharp, jagged mountains into smooth, rolling mountains and hills" (p. 148s). Likewise, the notion of very slow change is implicit in discussions of the rates of the movement of continents (pp. 297-303s), but it is not explicated.

The idea of slow change also is implicit in a few activities. For example, the Using Math section (p. 301s) asks students to calculate how far apart North America and Africa will be in 200 million years. Similarly, the second item 4 of Activity 11-2 (p. 306s) has students determine when Africa was at or near the Mid-Atlantic Ridge. In both cases, though, the material focuses on continental movement and not on the key idea that small and slow but continuous changes to the Earth's surface result in significant changes over time.

Idea f: Matching coastlines and similarities in rocks and fossils suggest that today’s continents are separated parts of what was a single vast continent long ago.

There is a content match. The beginning part of Chapter 11: Tectonics focuses on the historic evidence for continental drift. The single continental landmass of Pangaea and the evidence for it are discussed (pp. 294-297s). Figure 11-4 shows a time-lapse sequence of three representations of the probable break-up of Pangaea (p. 297s). The matching of coastlines (p. 295s) and fossil evidence is discussed (pp. 294-296s).

The text includes relevant activities. For example, some students use clay to make models of continents and place objects that represent fossils in the clay, while other students try to reconstruct the continents' original locations (p. 296s).

Idea g: The solid crust of the Earth consists of separate plates that move very slowly, pressing against and sliding past one another in some places, pulling apart in other places.

There is a content match. Plates are defined by text and by representation (p. 304s), as are the three types of plate boundaries (pp. 305-309s). Examples of plate movements and events at plate boundaries, such as mountain formation, volcanoes, and earthquakes, are discussed (pp. 307s, 311s, 312s, 315s).

Chapter 11: Plate Tectonics also provides activities, demonstrations, and practice questions. For example, students are asked to calculate spreading rates at the Mid-Atlantic Ridge (p. 306s) and, after studying Figure 11-10, to illustrate the different plate boundaries (p. 308st).

Idea h: Landforms and major geologic events, such as earthquakes, volcanic eruptions, and mountain building, result from these plate motions.

There is a content match. The idea is addressed and represented in Chapter 9: Earthquakes and Chapter 10: Volcanoes. Two figures (9-2 on page 237s; 10-3 on page 268s) show the location of earthquakes and volcanoes in relation to plate boundaries. Additionally, in Chapter 11: Plate Tectonics, Figure 11-10 (pp. 308-309s) explicitly relates divergent and convergent plate boundaries to landforms of mountains, rift valleys, mid-ocean ridges, volcanic island arcs, and trenches. Many of the landforms and geologic events that occur as a result of tectonic plate movement are discussed in the text (particularly on pages 304-313s). For example, students read about the Himalayan and Appalachian mountains being formed by converging continental plates (p. 312s).

The Teacher Wraparound Edition includes questions for students, such as: "Earthquakes are associated with some plate boundaries. Why do you think this is so?" (p. 311t).

Building a Case

Most of the key Earth science ideas are presented as text assertions that are often accompanied by illustrative examples. However, the text makes some attempt to provide an evidenced-based argument for the key idea that matching coastlines and similarities in rocks and fossils suggest that today's continents are separated parts of what was a single vast continent long ago (Idea f). In Chapter 11: Plate Tectonics, a reading section entitled "Evidence for Continental Drift" presents several lines of evidence, including the matching coastlines of continents, similar fossils and matching rock structures found on now-far-spread continents, and tropical fossils found on an island in the Arctic, as well as glacial markings found in places where no glaciers exist today (pp. 294-296s). One statement explains that "Wegener's early evidence has since been joined by other important proofs. Let's explore both Wegener's clues and some newer ones" (p. 295s).

Although several important pieces of evidence for continental drift are presented, the argument that links them to the conclusions is not explained in sufficient detail to be understood by students. In some places in the student text, alternative explanations for the evidence for continental drift are refuted, but the arguments are incomplete. For example, the text notes that Mesosaurus fossils have been found in South America and Africa and that "this swimming reptile lived in fresh water and on land..It's very unlikely that it could have swum between the continents" (p. 295s). However, it does not explain why. Such information as the small size of the reptile and the fact that ocean water is salty, which is a deadly environment for freshwater organisms, would have helped students to understand why the alternative explanation does not fit. Similarly, the text does not explain why it is unlikely that the Mesosaurus could have evolved independently in both locations. Similarly, the text explains that "[f]ossils of warm-weather plants were found on the island of Spitzbergen in the Arctic Ocean. Wegener believed that Spitzbergen drifted from the tropic regions" (p. 296s). Although the text states both the evidence and Wegener's conclusion, it does not make the argument for how the two are linked. Specifically, it does not point out that an organism is typically suited for only one type of climate so it is unlikely that the same organism would have existed in such different climates, namely, Arctic and tropical regions. Furthermore, while it is possible that Arctic could have had a tropical climate in the past, the more plausible explanation for this (and other) evidence is that landmasses can move great distances.


The material reflects a significant problem with coherence, which is caused by inappropriate topic sequencing, the addition of unrelated topics, unexplained technical terminology, and a lack of the background information needed for comprehension. Many terms are used several pages or even several chapters before they are introduced with a definition and an explanation; for example, "faulting" is used to explain the creation of mountains on pages 123-124s, but is not defined until page 236s.

Likewise, the motion of plates is used to discuss earthquakes and volcanoes in Chapters 9: Earthquakes and Chapter 10: Volcanoes, but it is not defined or explained until Chapter 11: Plate Tectonics. An earthquake activity (9-1 on pages 242-243s) begins by telling students that they have learned about plates already, even though plates are not taught until chapter 11 (p. 304s). The purpose of Activity 9-1 is to have students plot earthquake depths and then "hypothesize what is happening to the plates at the Earth's surface in the vicinity of the plotted earthquake foci." However, students will not understand the activity or the real phenomenon it represents, nor will they comprehend the connection between the depth of earthquakes and plate movement, because the necessary plate tectonic information is not taught until much later. Many other parts of chapters 9 and 10 involve the use and understanding of plate tectonics before students have had opportunities to learn about it (e.g., p. 243st, Go Further; p. 271st, Analyze and Apply, item 3; p. 272t, Reteaching; p. 272s, Figure 10-4; and p. 273st, Section Wrap-up, items 1 and 3, and Skill Builder).

The coherence of the Earth science ideas presented in this material is diminished further by extraneous topics that seem to have been inserted into chapters randomly. In Chapter 7: Erosional Forces, some activities in the Teacher Wraparound Edition bring in the topic of climate change (pp. 182-183t). Another activity has students research Bowen's reaction series and then write a report about why some magmas are hotter than others (p. 277t). This activity introduces a topic that is well beyond science literacy and may be difficult for middle grades students because it involves such complex ideas as chemical reactions, phase changes, and how the physical properties of mixtures differ from those of the individual components.

Overall, Glencoe Earth Science has a significant problem with presenting information in a logical sequence that will be comprehensible to students, allow them to make connections between concepts, and help them to understand how scientific ideas are developed. The frequent insertion of unrelated or conceptually difficult material into the flow of chapters is distracting and confusing to students. They may have difficulties connecting the considerable amount of highly detailed information provided with the overarching concepts stated in the key ideas.

Beyond Literacy

The chapters evaluated in terms of the key Earth science ideas include several topics that are beyond science literacy as defined in Benchmarks for Science Literacy (AAAS, 1993) and National Science Education Standards (NRC, 1996) and that often interrupt the presentation of the key Earth science ideas. In a few cases, more advanced ideas are presented. For example, the discussion of moving tectonic plates includes an explanation of magnetic evidence for moving plates (pp. 300-303s). This discussion is not likely to be comprehensible to students and interrupts the basic story of plate tectonics. A similar problem occurs regarding the discussion of the chemical composition of different types of lava (pp. 277-278s). But more often, the text explanations include so many details of Earth-changing processes that the key ideas are obscured. For example, Chapter 9: Earthquakes presents information about compression, tension, shear, faults, fault surface, normal faults, reverse faults, and transform or strike-slip faults (pp. 237-238s). Similarly, Chapter 7: Erosional Forces presents technical terms for glacial formations, such as "moraine," "till," "drumlin," "meltwater," "outwash plains," "arete," "horn," "cirque," "plucking," "striations," "esker," "erratic," and "kettle lakes" (pp. 182-185s). And, Chapter 10: Volcanoes emphasizes such terms as "intrusive igneous rocks," "batholiths," "volcanic neck," "laccolith," "fissure," "sill," "dike," "crater," "caldera," "vent," and "magma chamber" (pp. 283-286s), rather than how volcanoes contribute to the changing surface of the Earth. None of these details and technical terms are included in Benchmarks for Science Literacy or National Science Education Standards, and their inclusion in the student text may encourage teachers to emphasize vocabulary over the key Earth science ideas.


The evaluation teams developed a summary assessment of the most common kinds of errors found in each of the three subject areas-physical science, Earth science, and life science. In this context, "errors" is taken to mean not only outright inaccuracies, but also those instances in which the material is very likely to lead to or support student misconceptions. Overall, inducement to misconstrue is the most serious problem of accuracy in the evaluated materials.

The evaluation teams' collective findings, presented below, should be taken as having general applicability to all of the evaluated materials, not complete and specific applicability in toto to any one of them.

Identified errors occur most frequently in drawings and other diagrams. They take the form of representations that are likely to either give rise to or reinforce misconceptions commonly held by students. Following are Earth science examples of the kinds of misleading illustrative materials of most concern to the evaluation teams:

  • Maps that do not show the accurate locations of earthquakes and volcanoes will prevent students from understanding the relationship between these events and plate boundaries. Likewise, diagrams and maps that do not include legends, and photographs that do not explain the size and scale of the object seen, are difficult for students to understand.

  • Diagrams that (a) depict plates moving away from one another, thus exposing the mantle, (b) show the mantle very close to the surface of the Earth, or (c) show plates as being a layer under the crust inaccurately represent the structure of the Earth and the motion of plates.

  • Diagrams that show the melting of subducted plates are incorrect. Subducting plates are known to cause melting in the mantle, and thus nearby volcanic activity, but the plates do not melt.