Earth’s history spans 4.6 billion years. As rock strata form, they create a record of major events, including climate change, natural disasters, and mass extinctions.
For instance, a black coal seam (shown here) is evidence that an area’s climate was once warm and humid. This is because coal forms from the remains of plants that grow in those conditions.
1
Thicker strata can form when sediment piles up very quickly. Which three events could cause this to occur?
Flooding
Landslides
Animal migration
Volcanic eruptions
Gentle ocean currents
Natural disasters leave their mark in rock strata, too. Volcanic eruptions release ash that can be incorporated into rock strata (shown below, left). Depending on the type of volcano and the minerals present, ash layers can appear black, white, red, pink, purple, yellow, or green.
In addition, earthquakes can create folds, cracks, and tilting in rock strata (shown below, right). Meteorites leave behind impact craters and shiny minerals that form as a result of extreme heat and pressure.
On the left, rock strata of different thicknesses, colors, and textures. The lower strata are thick, matte, and black. Above that, there are a few thin, light-colored strata. Farther up, there is a thick pink layer followed by a thick, black layer and a final tan layer. On the right, alternating tan, white, and brown rock strata are visible above sandy, rocky land. The rock strata are folded sharply like an accordion.
While the fossils found in rock strata tell us about former life on Earth, a lack of fossils also provides information. The sudden disappearance of many types of fossils between layers suggests a mass extinction occurred.
2
The image on the left (above) shows several layers of volcanic ash. Which two statements could explain why these layers vary in thickness?
Each volcanic eruption caused the land to tilt
Earthquakes prevented some of the ash from settling
Some eruptions produced more ash than others
Some volcanoes were closer to this area than others
Some of the ash layers formed as a result of meteors
3
Imagine that fish fossils are found in the middle of the folded rock strata shown above (right). Use this information to fill in the blanks to complete the sentence. Not all answer choices will be used.
The presence of fish fossils suggests that this area was once covered by
. This must have occurred
the earthquake that caused the strata to fold.
4
This image shows a diagonal stripe of granite passing upward through layers of rock. Is this granite older or younger than the rock it passes through? How do you know?
A close-up photo of a gray rock with a visible crack going vertically down its right side. There is also a thick white band embedded in the gray rock, traveling diagonally from the bottom left to the top right.
Observation
0
1 answer
The three events that could cause thick strata to form when sediment piles up quickly are:
Flooding
Landslides
Volcanic eruptions
The two statements that could explain why the layers of volcanic ash vary in thickness are:
Some eruptions produced more ash than others.
Some volcanoes were closer to this area than others.
The presence of fish fossils suggests that this area was once covered by water. This must have occurred before the earthquake that caused the strata to fold.
The granite is younger than the rock it passes through. This is known because of the principle of cross-cutting relationships in geology, which states that a rock or geological feature that cuts through another is younger than the rock it disrupts. Since the granite is passing through the layers of rock, it must have formed after those layers were already deposited.
