Rock Cycle and Geological Time
Rocks are constantly being formed, broken down, and reformed over millions of years. The rock cycle describes these transformations, and geological time provides the vast timescale over which they occur.
What You Need to Know
Key Concept Diagram
The three rock types are igneous (from cooling magma), sedimentary (from compacted sediments), and metamorphic (changed by heat and pressure)
The rock cycle shows how rocks transform between the three types over geological time
Geological time is measured in millions of years; Earth is approximately 4.5 billion years old
Radioactive dating uses the decay of isotopes to determine the age of rocks and fossils
Key Vocabulary
Igneous rock
Rock formed from cooled and solidified magma or lava
Sedimentary rock
Rock formed from compressed and cemented sediment particles
Metamorphic rock
Rock that has been changed by heat and/or pressure without melting
Geological time
The vast timescale of Earth's history, measured in millions to billions of years
Knowledge Check
Select the correct answer for each question. Click "Check Answer" to see if you are right.
Question 1
Magma from a volcano cools and solidifies on Earth's surface. What type of rock forms?
Question 2
Over millions of years, limestone (sedimentary rock) is buried deep underground where heat and pressure are intense. What type of rock may it become?
Question 3
Earth is approximately how old?
Key Concepts Summary
- ●The three rock types are igneous (from cooling magma), sedimentary (from compacted sediments), and metamorphic (changed by heat and pressure)
- ●The rock cycle shows how rocks transform between the three types over geological time
- ●Geological time is measured in millions of years; Earth is approximately 4.5 billion years old
- ●Radioactive dating uses the decay of isotopes to determine the age of rocks and fossils