Rock Layers
In undisturbed rock layers, this layer is the oldest.
bottom layer
Preserved remains or traces of ancient living things found in rock.
fossil
The breaking of rock into smaller pieces by water, ice, wind, or acid.
weathering
Underground caves with marine fossils inside limestone were most likely formed by this process.
erosion by water
The slow movement of continents by moving tectonic plates.
continental drift
This rule says that lower undisturbed rock layers are older than layers above them.
Law of Superposition
Fossils of fish and marine crustaceans show that an area was once this environment.
underwater or an ocean environment
The movement of broken rock or soil to a new place.
erosion
An ocean basin may grow larger or smaller because of this slow movement of Earth’s crust.
plate movement or continental drift
The tool scientists use to measure extremely slow plate movement.
GPS
A crack or intrusion that cuts through other rock layers is this compared with those layers.
younger
When all members of a species die out, it is called this.
extinction
The dropping of eroded sediment in a new location.
deposition
A rock layer contains fossils below it but none above it, along with a thin ash layer. This most likely occurred.
volcanic eruption
When oceanic crust sinks beneath continental crust, this process occurs.
subduction
This type of dating compares whether rocks are older or younger without giving an exact age.
relative dating
A layer high in this element can be evidence of an asteroid impact.
iridium
A gradual sequence from shallow ocean to tidal zone to coastal plain shows this type of environmental change.
gradual change
Two continents collide, and neither crust sinks underneath the other. This creates this landform.
large mountain range
This collision forms the largest mountain ranges, such as the Himalayas.
continent-continent collision
This timeline organizes Earth’s past into eons, eras, periods, and epochs.
geologic time scale
Dinosaur fossils below an iridium-rich layer but not above it support this event.
an asteroid impact that caused extinction
An ash layer followed by missing fossils is evidence of this sudden event.
volcanic eruption
A mountain range that becomes shorter, rounder, and less steep over millions of years has been changed by these two processes.
weathering and erosion
Over millions of years, weathering and erosion make jagged mountains become this.
shorter, rounder, and less steep mountains