Earth Science Quiz: Relative Dating Principles

What this quiz covers

This quiz focuses on Relative Dating Principles, giving you a quick way to practice the rules, question types, and explanations that matter most for Earth Science.

How to use this quiz

Try each quiz question before looking at the correct answer. Use the explanations to review missed ideas, then come back to similar questions until the pattern feels familiar.

Question 1

1. The principle of superposition, indicating the sandstone is younger than the gneiss.
2. The principle of cross-cutting relationships, indicating the sandstone filled cracks in the gneiss.
3. The formation of a nonconformity, representing deposition on an eroded surface of older crystalline rock. (correct answer)
4. The formation of an angular unconformity, representing deposition on tilted sedimentary layers.

Explanation: A nonconformity is a specific type of unconformity where sedimentary rocks are deposited directly on top of older, eroded igneous or metamorphic rocks (crystalline rocks). The gneiss is a metamorphic rock, and the sandstone is sedimentary. The erosional surface between them represents a significant time gap during which the gneiss was formed, uplifted, and eroded before the sand was deposited. While superposition also applies (sandstone is younger), the term 'nonconformity' specifically describes this entire relationship and the major time gap it implies.

Question 2

1. The sill is an ancient lava flow that was buried by the sandstone, with heat from burial causing metamorphism.
2. The sill is younger than both the shale and the sandstone because it intruded between them after they were both present. (correct answer)
3. The sill is older than the sandstone but younger than the shale, forming a surface on which the sand was deposited.
4. The sill and the sandstone are younger than the shale, but their relative ages cannot be determined from this evidence.

Explanation: Contact metamorphism occurs when hot magma comes into contact with existing rock. The presence of a 'baked' zone on the shale below and the sandstone above indicates that both layers were already in place when the molten rock intruded. This makes the sill younger than both layers it is between, according to the principle of cross-cutting relationships. If it were a lava flow (older than the sandstone), there would be no contact metamorphism on the bottom of the sandstone.

Question 3

1. The granite pluton is younger because it intruded into the base of the conglomerate layer, baking the contact.
2. The conglomerate is younger because it contains inclusions of the granite, which had to exist and be eroded first. (correct answer)
3. The two rock units are approximately the same age, formed during the same mountain-building event.
4. The conglomerate is older, and the granite inclusions were chemically precipitated within it during diagenesis.

Explanation: The principle of inclusions states that any rock fragments (clasts or inclusions) found within another rock must be older than the rock in which they are contained. Here, the conglomerate contains pebbles of the granite. This means the granite had to form, be uplifted, weathered, and eroded to produce the pebbles before the sediment that formed the conglomerate could be deposited. Therefore, the conglomerate is younger than the granite pluton.

Question 4

1. Was the granite intrusion younger or older than the sandstone layer it cuts through?
2. Did the faulting occur before or after the sedimentary layers were tilted?
3. How many millions of years passed during the time represented by the disconformity? (correct answer)
4. Are the fossils in the top layer younger than the fossils in the bottom layer?

Explanation: Relative dating principles (superposition, cross-cutting, inclusions) allow geologists to determine the sequence of events (what happened before what), but they do not provide numerical ages. To determine the duration of a time gap, such as an unconformity, in millions of years, absolute dating methods (like radiometric dating) of layers above and below the gap are required. The other questions can all be answered by applying relative dating principles to the geometric relationships between rock units.

Question 5

1. Granite, sandstone, basalt dike (correct answer)
2. Sandstone, granite, basalt dike
3. Basalt dike, sandstone, granite
4. Granite, basalt dike, sandstone

Explanation: When you encounter geological formations with different rock types and structures, you need to apply the principles of relative dating to determine the sequence of events. The key is recognizing that certain geological relationships tell us about timing. Let's work through this step by step. Since the sandstone contains inclusions of granite, the granite must have existed first and been weathered to provide fragments for the sedimentary rock. You can't include pieces of something that doesn't exist yet. Additionally, since the basalt dike cuts through the sandstone layer, the dike must be younger than the sandstone it intrudes. Igneous intrusions always occur after the rocks they cut through. This gives us the sequence: granite (oldest) → sandstone → basalt dike (youngest), which is answer choice A. Answer choice B incorrectly places sandstone before granite, but this is impossible since the sandstone contains granite fragments. Choice C puts the basalt dike first, which contradicts the fact that dikes intrude into pre-existing rocks. Choice D places the basalt dike before the sandstone, again ignoring the intrusive relationship where the dike cuts through the sandstone. Remember the fundamental rule: inclusions are older than the rock containing them, and intrusions are younger than the rock they cut through. When you see inclusions and cross-cutting relationships in geology problems, immediately think about what had to exist first for these relationships to form. This logical approach will help you sequence geological events correctly every time.

Question 6

1. A fine-grained, vesicular (bubbly) texture in the upper portion of the igneous body. (correct answer)
2. The presence of contact metamorphism on the rock layer below the igneous body.
3. Inclusions of the overlying sedimentary rock found within the igneous body.
4. The igneous body has a chemical composition identical to a nearby volcano.

Explanation: When distinguishing between buried lava flows and intrusive sills, you need to focus on evidence that reveals how and where the magma cooled. Both are tabular igneous bodies, but lava flows formed at Earth's surface before being buried, while sills formed underground when magma intruded between existing rock layers. The key evidence is a fine-grained, vesicular texture in the upper portion (A). This bubbly texture forms when gas bubbles are trapped as lava cools rapidly at the surface. The fine-grained upper portion indicates quick cooling in contact with air or water. Intrusive sills cool slowly underground and develop coarse-grained textures without vesicles, since the overlying pressure prevents gas bubble formation. Contact metamorphism below the igneous body (B) occurs with both buried lava flows and sills, since both involve hot igneous material in contact with existing rocks. This evidence doesn't distinguish between them. Inclusions of overlying sedimentary rock (C) would actually suggest an intrusive sill, where magma incorporated pieces of the rock it intruded through. A lava flow wouldn't contain inclusions from rocks that were deposited on top of it later. Identical chemical composition to a nearby volcano (D) could apply to both features, since sills can have the same magma source as surface eruptions. Remember this pattern: vesicular textures are your smoking gun for surface volcanic activity. The combination of vesicles plus fine-grained texture in the upper portion uniquely indicates rapid cooling at Earth's surface—the hallmark of a lava flow.

Question 7

1. angular unconformity, indicating a period of tectonic tilting and erosion.
2. nonconformity, where sedimentary rock was deposited on older igneous rock.
3. fault contact, where rock layers have been displaced next to each other.
4. disconformity, representing a period of erosion or non-deposition without tilting. (correct answer)

Explanation: A disconformity is a type of unconformity where the sedimentary layers above and below the erosional surface are parallel. The key evidence is the missing time in the fossil record (the entire Silurian period is absent). This indicates that either deposition stopped for a long period, or layers were deposited and then later eroded away before Devonian deposition began. Since the layers are parallel, it is a disconformity, not an angular unconformity. It is not a nonconformity because the underlying rock is sedimentary, not igneous/metamorphic.

Question 8

1. The principle of superposition, with the sandstone being the lower, older layer.
2. The principle of cross-cutting relationships, as the pluton cuts the sandstone.
3. The principle of lateral continuity, by tracing the sandstone layer to the pluton.
4. The principle of inclusions, indicating the sandstone is older than the granite. (correct answer)

Explanation: A xenolith is a type of inclusion. The principle of inclusions states that the included rock (the xenolith) must be older than the rock that encloses it (the igneous intrusion). For the sandstone xenolith to be inside the granite, the sandstone must have existed first, been broken off, and then incorporated into the magma before it solidified. Therefore, the sandstone is older than the granite.

Question 9

1. angular unconformity, indicating a period of tectonic tilting and erosion.
2. nonconformity, where sedimentary rock was deposited on older igneous rock.
3. fault contact, where rock layers have been displaced next to each other.
4. disconformity, representing a period of erosion or non-deposition without tilting. (correct answer)

Explanation: A disconformity is a type of unconformity where the sedimentary layers above and below the erosional surface are parallel. The key evidence is the missing time in the fossil record (the entire Silurian period is absent). This indicates that either deposition stopped for a long period, or layers were deposited and then later eroded away before Devonian deposition began. Since the layers are parallel, it is a disconformity, not an angular unconformity. It is not a nonconformity because the underlying rock is sedimentary, not igneous/metamorphic.

Question 10

1. The principle of superposition, indicating the sandstone is younger than the gneiss.
2. The principle of cross-cutting relationships, indicating the sandstone filled cracks in the gneiss.
3. The formation of a nonconformity, representing deposition on an eroded surface of older crystalline rock. (correct answer)
4. The formation of an angular unconformity, representing deposition on tilted sedimentary layers.

Explanation: A nonconformity is a specific type of unconformity where sedimentary rocks are deposited directly on top of older, eroded igneous or metamorphic rocks (crystalline rocks). The gneiss is a metamorphic rock, and the sandstone is sedimentary. The erosional surface between them represents a significant time gap during which the gneiss was formed, uplifted, and eroded before the sand was deposited. While superposition also applies (sandstone is younger), the term 'nonconformity' specifically describes this entire relationship and the major time gap it implies.

Question 11

1. The principle of superposition, with the sandstone being the lower, older layer.
2. The principle of cross-cutting relationships, as the pluton cuts the sandstone.
3. The principle of lateral continuity, by tracing the sandstone layer to the pluton.
4. The principle of inclusions, indicating the sandstone is older than the granite. (correct answer)

Explanation: A xenolith is a type of inclusion. The principle of inclusions states that the included rock (the xenolith) must be older than the rock that encloses it (the igneous intrusion). For the sandstone xenolith to be inside the granite, the sandstone must have existed first, been broken off, and then incorporated into the magma before it solidified. Therefore, the sandstone is older than the granite.

Question 12

1. Was the granite intrusion younger or older than the sandstone layer it cuts through?
2. Did the faulting occur before or after the sedimentary layers were tilted?
3. How many millions of years passed during the time represented by the disconformity? (correct answer)
4. Are the fossils in the top layer younger than the fossils in the bottom layer?

Explanation: Relative dating principles (superposition, cross-cutting, inclusions) allow geologists to determine the sequence of events (what happened before what), but they do not provide numerical ages. To determine the duration of a time gap, such as an unconformity, in millions of years, absolute dating methods (like radiometric dating) of layers above and below the gap are required. The other questions can all be answered by applying relative dating principles to the geometric relationships between rock units.

Question 13

1. The sill is an ancient lava flow that was buried by the sandstone, with heat from burial causing metamorphism.
2. The sill is younger than both the shale and the sandstone because it intruded between them after they were both present. (correct answer)
3. The sill is older than the sandstone but younger than the shale, forming a surface on which the sand was deposited.
4. The sill and the sandstone are younger than the shale, but their relative ages cannot be determined from this evidence.

Explanation: Contact metamorphism occurs when hot magma comes into contact with existing rock. The presence of a 'baked' zone on the shale below and the sandstone above indicates that both layers were already in place when the molten rock intruded. This makes the sill younger than both layers it is between, according to the principle of cross-cutting relationships. If it were a lava flow (older than the sandstone), there would be no contact metamorphism on the bottom of the sandstone.

Question 14

1. The granite pluton is younger because it intruded into the base of the conglomerate layer, baking the contact.
2. The conglomerate is younger because it contains inclusions of the granite, which had to exist and be eroded first. (correct answer)
3. The two rock units are approximately the same age, formed during the same mountain-building event.
4. The conglomerate is older, and the granite inclusions were chemically precipitated within it during diagenesis.

Explanation: The principle of inclusions states that any rock fragments (clasts or inclusions) found within another rock must be older than the rock in which they are contained. Here, the conglomerate contains pebbles of the granite. This means the granite had to form, be uplifted, weathered, and eroded to produce the pebbles before the sediment that formed the conglomerate could be deposited. Therefore, the conglomerate is younger than the granite pluton.

Question 15

1. Granite, sandstone, basalt dike (correct answer)
2. Sandstone, granite, basalt dike
3. Basalt dike, sandstone, granite
4. Granite, basalt dike, sandstone

Explanation: When you encounter geological formations with different rock types and structures, you need to apply the principles of relative dating to determine the sequence of events. The key is recognizing that certain geological relationships tell us about timing. Let's work through this step by step. Since the sandstone contains inclusions of granite, the granite must have existed first and been weathered to provide fragments for the sedimentary rock. You can't include pieces of something that doesn't exist yet. Additionally, since the basalt dike cuts through the sandstone layer, the dike must be younger than the sandstone it intrudes. Igneous intrusions always occur after the rocks they cut through. This gives us the sequence: granite (oldest) → sandstone → basalt dike (youngest), which is answer choice A. Answer choice B incorrectly places sandstone before granite, but this is impossible since the sandstone contains granite fragments. Choice C puts the basalt dike first, which contradicts the fact that dikes intrude into pre-existing rocks. Choice D places the basalt dike before the sandstone, again ignoring the intrusive relationship where the dike cuts through the sandstone. Remember the fundamental rule: inclusions are older than the rock containing them, and intrusions are younger than the rock they cut through. When you see inclusions and cross-cutting relationships in geology problems, immediately think about what had to exist first for these relationships to form. This logical approach will help you sequence geological events correctly every time.

Question 16

1. Fault M is younger than Dike N because the dike is offset by the fault. (correct answer)
2. Dike N is younger than Fault M because the dike cuts across the fault without being offset.
3. Fault M and Dike N are the same age because they both cut through the limestone unit.
4. Dike N is younger than the sandstone but older than Fault M, which occurred after all deposition.

Explanation: The principle of cross-cutting relationships states that a geologic feature which cuts another is the younger of the two. In the diagram, Dike N is clearly cut and displaced by Fault M. Therefore, Dike N must have existed first for the fault to offset it. This makes Fault M younger than Dike N.

Question 17

1. The fault is older than layer C but younger than intrusion E.
2. The fault is younger than layer C but older than layer D. (correct answer)
3. The fault is the youngest feature in the cross-section.
4. The fault is older than intrusion E and layer C.

Explanation: Let's trace the events. Layers A and B were deposited. Intrusion E cut through A and B. Then an unconformity formed, eroding the top of A, B, and E. Layer C was deposited on this unconformity. After C was deposited, the fault occurred, as it cuts through A, B, and C. Finally, layer D was deposited on top of everything, including the fault, because layer D is not cut by the fault. This means the faulting event happened after the deposition of layer C but before the deposition of layer D.

Question 18

1. Superposition, then Cross-cutting relationships. (correct answer)
2. Inclusions, then Superposition.
3. Cross-cutting relationships, then Superposition.
4. Superposition, then Inclusions.

Explanation: To determine that the limestone is younger than the shale, one must assume the layers were deposited sequentially in an undisturbed sequence. The limestone lies on top of the shale, so the principle of superposition is used first. To determine that the limestone is older than the fault, one must observe that the fault cuts through the limestone layer. The principle of cross-cutting relationships states that the feature that is cut is older than the feature that does the cutting. Therefore, superposition is used to date the layers relative to each other, and then cross-cutting relationships are used to date the fault relative to the layers.

Question 19

1. A diagram where a fault cuts limestone and shale, but not the granite dike or the overlying sandstone.
2. A diagram where a granite dike cuts through limestone but stops at the shale layer, with unfaulted sandstone on top.
3. A diagram where a fault cuts through limestone, shale, and a granite dike, with a horizontal layer of sandstone resting on the eroded, faulted surface. (correct answer)
4. A diagram where limestone and shale are folded, cut by a dike and a fault, and overlain by sandstone.

Explanation: This question requires visualizing the sequence. 1 & 2: Limestone is below shale (superposition). 3: The granite dike must cut through both limestone and shale (cross-cutting). 4: The fault must cut through the limestone, shale, and the dike (cross-cutting). 5 & 6: An erosional surface must cut across all the previously mentioned features, and the sandstone must be deposited horizontally on top of this surface. Choice C is the only one that shows the fault cutting all three older units and the sandstone lying on top of the resulting unconformity.

Question 20

1. The deposition of the shale layer.
2. The intrusion of the granite pluton (Unit G).
3. Movement along the fault (Fault F). (correct answer)
4. The folding of the sedimentary layers.

Explanation: To find the event immediately preceding the erosion of Surface X, we must determine the sequence of events affecting the rocks below Surface X. The layers (shale, limestone) were deposited, then folded. The granite pluton (G) cuts the folds, so it is younger than the folding. The fault (F) cuts the folded layers and the pluton, so it is the youngest event before the erosion. The erosion that created Surface X then cut across all of these features (the folded layers, the pluton, and the fault). Therefore, movement along Fault F was the last event before the period of erosion began.