Rock Cycle
Heat and pressure turn existing rocks into this "change of form" category.
We are currently living in this Era, known as the "Age of Mammals."
Cenozoic Era
These fossils are used to define and identify geologic periods because they were widespread but short-lived.
Index Fossil
This is the solid, outermost layer of the Earth.
Crust
The process of sediments being glued together to form sedimentary rock.
Cementation
This "Event" about 541 million years ago saw a huge burst in the diversity of animal life.
Cambrian Explosion
This law states that in undisturbed rock layers, the oldest layer is at the bottom.
Law of Superposition
The theory that Earth's outer shell is divided into several plates that glide over the mantle.
Plate Tectonics
This specific type of rock often contains fossils because it forms at low temperatures and pressures.
The Mesozoic Era ended with a mass extinction caused by an asteroid, famously killing off these creatures.
Dinosaurs
This type of fossil isn't a body part, but a sign of activity, like a footprint or a burrow.
Trace Fossil
Magma that reaches the Earth's surface is called this.
Lava
When rocks are pushed deep into the Earth and turn back into magma, this process is occurring.
Melting
Earth is approximately this many billions of years old.
4.6 Billion
The method used to find the "exact" age of a fossil using radioactive isotopes.
Absolute Dating
This is the supercontinent that existed roughly 300 million years ago.
Pangea
This type of rock is formed from the cooling of magma or lava.
igneous
Scientists divide Earth's history into these four largest chunks of time.
Eons
The preserved remains or traces of an organism that lived in the past.
Fossil
The process where rocks are broken down by wind, water, or ice.
Weathering