It’s About Time!
This is the system scientists use to organize Earth’s history.
What is the geologic time scale?
This type of fossil shows the preserved remains of an organism’s body.
What is a body fossil?
This principle states that in undisturbed rock layers, the oldest is at the bottom.
What is the Law of Superposition?
The idea that geologic processes happening today also happened in the past.
What is uniformitarianism?
Rock formed from cooled magma or lava.
What is an igneous rock?
The geologic time scale is based largely on evidence from these preserved remains or traces of organisms.
What are fossils?
Footprints, burrows, and droppings are examples of these fossils.
What are trace fossils?
A rock layer that cuts through other layers is always younger.
What is the Principle of Cross-Cutting Relationships?
The idea that sudden, violent events shaped Earth’s surface in the past.
What is catastrophism?
Rock formed from particles of other rocks pressed and cemented together.
What is a sedimentary rock?
The geologic time scale shows changes in Earth and life, most often marked by these events.
What are major extinctions and evolutionary changes?
This is the process by which minerals replace all or part of an organism.
What is petrification (permineralization)?
A gap in the geologic record caused by erosion or lack of deposition.
What is an unconformity?
This principle states that sedimentary rocks form in flat, horizontal layers.
What is the Principle of Original Horizontality?
Rock formed when heat and pressure change existing rock.
What is a metamorphic rock?
Geologic time is so vast that scientists compare it to this everyday concept to help understand it.
What is a calendar or clock?
This fossil fuel comes from the remains of ancient plants.
What is coal?
Fossils used to define and identify specific periods of time.
What are index fossils?
This principle states that if a rock contains fragments of another rock, the fragments must be older than the rock they are in.
What is the Principle of Inclusions?
The process by which sediments are dropped off in a new location.
What is deposition?
The geologic time scale is divided into four main units, from largest to smallest.
What are eons, eras, periods, and epochs?
This is the science of studying fossils.
What is paleontology?
This is the method of determining if one rock layer is older or younger than another without exact dates.
What is relative dating?
This principle says that layers of sediment extend sideways in all directions until they thin out or run into a barrier.
What is the Principle of Lateral Continuity?
The continuous process that changes one rock type into another.
What is the rock cycle?