5.7: Detailed Figure Descriptions

Figure 5.1.6: Fossil Succession

This image shows two separated rock columns with layered strata and fossils, illustrating how geologists correlate rock layers across distance using fossil evidence to match equivalent layers. It shows how fossil correlation is used to identify equivalent rock layers across different locations and reconstruct geologic history.Lines drawn between the columns indicate correlations. On the left and right sides are vertical stacks of horizontal rock layers. Each layer is shown as a distinct band, separated by clear boundaries. The two columns are separated by a gap, representing missing or eroded rock between locations. Within each layer are fossil illustrations. These fossils vary in shape and type and are used as identifying markers for each layer. Matching fossils appear in corresponding layers on both sides.

Several diagonal lines extend across the gap from layers on the left column to layers on the right column. These lines connect layers that contain the same fossil types, showing how they are correlated even though they are physically separated. The layers are distinguished by position, fossil content, and boundaries rather than color alone. The fossils provide the key evidence for matching layers. 

Figure 5.2.1: Stages in the Formation of a Non-Conformity

This diagram shows a three-step sequence of geologic change over time, read from left to right using arrows between panels. It shows  intrusive igneous rock forms forming first below the surface, which are later covered by younger sedimentary layers.

In the first panel, several flat, horizontal sedimentary layers sit above a lower rock unit. Inside that lower unit, the text “Intrusive Igneous Rock” is written. This unit also features a repeated short-line texture, while the layers above are smooth, parallel bands. The boundary between them is uneven, showing the igneous rock formed beneath earlier material.

An arrow points to the second panel. The arrows indicate the sequence of events. In the second panel, the entire block is composed of the same textured rock, with no sedimentary layers present and no additional text shown. Another arrow points to the third panel.In the third panel, horizontal sedimentary layers appear again above the same textured rock unit. The boundary between them remains uneven, and the layered bands are clearly distinct from the textured rock below.

Figure 5.2.2: Stages in the Formation of an Angular Unconformity

This image shows a three-step sequence of geologic change over time, read from left to right using arrows, illustrating how rock layers are first deposited horizontally, then tilted by geologic forces, and later covered by younger, flat-lying layers.

Across all panels, layers are distinguished by line orientation and position rather than color, and arrows indicate the sequence of events over time. In the first panel, multiple horizontal rock layers are depicted as flat, parallel bands stacked on top of one another. The top surface is uneven, representing the land surface. An arrow points to the second panel. In the second panel, those same layers are no longer horizontal. Instead, they are tilted diagonally from lower left to upper right. The layers remain parallel to each other, but their orientation has changed. The top surface is still uneven. Another arrow points to the third panel. In the third panel, a new set of horizontal layers appears at the top. These newer layers are flat and parallel, clearly oriented differently from the tilted layers below. The boundary between the tilted layers and the horizontal layers is uneven, indicating a break in deposition. The tilted layers remain visible beneath the newer horizontal layers.

Figure 5.2.3: Stages in the Formation of a Disconformity

This image shows a three-step sequence of geologic change over time, read from left to right using arrows, illustrating how originally flat sedimentary layers can be disturbed and later preserved as a buried, uneven layer within otherwise horizontal strata. Arrows between the panels indicate the sequence of events.

In the first panel, several horizontal rock layers are shown as flat, parallel bands stacked on top of each other. The top surface is uneven, representing land surface. In the second panel, the same horizontal layers remain, still flat and parallel, with no visible disturbance. In the third panel, a middle layer becomes uneven and wavy, forming a distinct boundary that contrasts with the flat, parallel layers above and below. The surrounding layers remain horizontal, clearly distinguishing the irregular shape of this layer.

Figure 5.2.4: Cross-section of Grand Canyon geologic units

This image is a vertical diagram of Grand Canyon rock layers, showing their names, order, and relative ages from top to bottom and shows how geologists interpret rock order, deformation, and unconformities to identify gaps in Earth’s geologic history. A labeled boundary called “The Great Unconformity” marks a gap in the geologic record. Arrows indicate vertical relationships between layers. At the top are Layered Paleozoic Rocks, shown as flat, horizontal layers. A numbered list identifies:

1. Kaibab Formation (Fm)
2. Toroweap Formation
3. Coconino Sandstone
4. Hermit Formation
5. Supai Group
6. Surprise Canyon Fm
7. Redwall Limestone
8. Temple Butte Fm
9. Muav Limestone
10. Bright Angel Shale
11. Tapeats Sandstone

The lower part of this section includes the Tonto Group (units 9–11), with arrows reinforcing layer order. Below this is an uneven, wavy boundary labeled “The Great Unconformity,” indicating erosion or missing time. Under this boundary are Grand Canyon Supergroup Rocks, shown as tilted layers. A list identifies:

12. Sixtymile Formation
13. Chuar Group
14. Nankoweap Fm
15. Unkar Group

At the bottom are Vishnu Basement Rocks, labeled:

16. Schists
17. Granites
18. Elves Chasm Gneiss

Figure 5.3.1: Geologic Range Chart

This image is a vertical bar chart showing the age ranges of four fossil species labeled Species A, Species B, Species C, and Species D showing how overlapping fossil ranges are used to correlate rock layers and determine their relative ages. A vertical axis on the left is labeled “Age ranges (Ma)”, meaning millions of years ago, with values from about 1 at the top to 14 at the bottom. The scale increases downward, so lower positions represent older ages. Each species is shown as a vertical bar spanning its age range:

• Species A extends from about 7 to 14 million years ago.
• Species B extends from about 5 to 12 million years ago.
• Species C extends from about 1 to about 9 million years ago.
• Species D extends from about 3 to about 8 million years ago.

A horizontal highlighted band across the chart is labeled “7.0 to 8.3 Ma.” This band marks the time interval where multiple species overlap. Within this highlighted range, all four species are present, indicating a shared time period.

Figure 5.3.3: The main sutural patterns of ammonites

The image combines a timeline and fossil diagrams to compare three ammonoid groups—Goniatites, Ceratites, and Ammonites—showing how their age ranges and shell features help scientists identify fossils and understand evolutionary changes over geologic time. Arrows, labels, and patterns provide multiple ways to interpret the information.

At the top is a timeline labeled Cretaceous, Jurassic, Triassic, Permian, Carboniferous, and Devonian. Horizontal bars show when each group existed:

• Goniatites occur mainly from the Devonian through the Permian.
• Ceratites occur mainly in the Triassic.
• Ammonites extend from the Triassic through the Cretaceous.

The bars overlap, indicating periods when groups coexisted. Below the timeline are fossil images labeled Ammonites, Ceratites, and Goniatites, each showing a coiled shell. Next to the fossils are line diagrams labeled “Saddles” and “Lobes.” Arrows point to these features along the shell suture lines:

• Goniatites show simple, smooth curves.
• Ceratites show more complex patterns, with jagged lobes and smoother saddles.
• Ammonites show highly complex, detailed patterns in both lobes and saddles.

Figure 5.4.2: Protons, neutrons, and electrons in carbon isotopes

This illustration compares three carbon isotopes: carbon-12 (stable), carbon-13 (stable), and carbon-14 (radioactive), showing how differences in neutrons help explain stability and radioactive decay. A labeled key identifies particles, and each atom diagram uses position, labels, and counts rather than color alone. A key on the left labels three particle types:

• electron
• proton
• neutron

Each of the three diagrams shows an atom with a central nucleus and electrons moving in circular orbits around it. In all three atoms, the nucleus contains 6 protons, and this is labeled beneath each diagram. This confirms all three are carbon. The differences are in the number of neutrons:

• carbon-12 (stable) shows 6 protons and 6 neutrons
• carbon-13 (stable) shows 6 protons and 7 neutrons
• carbon-14 (radioactive) shows 6 protons and 8 neutrons

Electrons are shown orbiting each nucleus, with the same number in each diagram, indicating that electron count does not change between isotopes. Each isotope is labeled directly below its diagram with its name and whether it is stable or radioactive. This image illustrates that isotopes of the same element have the same number of protons but different numbers of neutrons, and that these differences affect whether the atom is stable or radioactive.

Figure 5.4.3: Alpha Particle

This image shows alpha decay, where an atomic nucleus emits a small particle, illustrating how radioactive decay changes an atom over time. In alpha decay, a nucleus loses 2 protons and 2 neutrons, changing into a different element.Lines indicate motion from left to right. On the left is a large atomic nucleus made up of many small spheres grouped together. These spheres represent protons and neutrons, forming a dense cluster. To the right of the nucleus is a smaller cluster of four spheres moving away. This smaller group is labeled with the Greek letter “α” (alpha). It represents an alpha particle, which consists of 2 protons and 2 neutrons. Thin lines between the large nucleus and the smaller cluster indicate the direction of movement, showing that the alpha particle is being emitted from the nucleus.

Figure 5.4.4: Radioactive Decay Curve 

This graph of radioactive decay over time, showing how a parent isotope decreases and a daughter isotope increases across half-lives, helping explain how scientists use predictable decay patterns to determine the age of rocks and fossils. Across the graph, the relationship between the two curves shows that each half-life reduces the parent isotope by half while increasing the daughter isotope by the same proportion. Axes, labels, symbols, and markers provide multiple ways to interpret the data, and arrows highlight key changes early in the process.

The horizontal axis is labeled “Half-lives passed” and runs from 0 to 8. The vertical axis is labeled “Percentage in sample” and runs from 0% to 100%. Two curves are shown:

• The Parent curve starts at 100% at 0 half-lives and steadily decreases: about 50% at 1 half-life, 25% at 2, about 12% at 3, and approaching 0% by 8 half-lives.
• The Daughter curve starts at 0% at 0 half-lives and increases: about 50% at 1 half-life, about 75% at 2, about 88–90% at 3, and approaching 100% by 8 half-lives.

A legend on the right labels the two curves as “Parent” and “Daughter.” Data points along each curve mark values at each half-life. Near the first half-life, two arrows are labeled:

• “A” points horizontally toward the midpoint, emphasizing the increase in daughter material.
• “B” points downward, emphasizing the decrease in parent material.