Elizabeth, a Licensed Massage Therapist, has a Master's in Zoology from North Carolina State, one in GIS from Florida State University, and a Bachelor's in Biology from Eastern Michigan University. She has taught college level Physical Science and Biology.
Relative vs. Absolute Time in Geology
About Time
How much of your life do you spend thinking about time? For geologists, the answer is a lot! Time comes in different forms in geology, mainly absolute and relative. They are both important in terms of Earth's history and its geological timeline, and they work together in concert to build the planet's geological record. In this lesson, we're going to discuss what each type of time is and why it is important so that you too can understand how they work to describe past events on Earth. Ready to get started?

An error occurred trying to load this video.
Try refreshing the page, or contact customer support.
You must cCreate an account to continue watching
Register to view this lesson
As a member, you'll also get unlimited access to over 84,000 lessons in math, English, science, history, and more. Plus, get practice tests, quizzes, and personalized coaching to help you succeed.
Get unlimited access to over 84,000 lessons.
Try it nowAlready registered? Log in here for access
BackResources created by teachers for teachers
I would definitely recommend Study.com to my colleagues. It’s like a teacher waved a magic wand and did the work for me. I feel like it’s a lifeline.
You're on a roll. Keep up the good work!
Just checking in. Are you still watching?
Yes! Keep playing.Absolute Time
Let's start with absolute time, also called chronometric time ('chrono' means 'time' and 'metric' means 'measure'). You can think of this type of time as how we normally view it on a day-to-day basis: specific intervals or moments measured in days, months, years, etc. For example, 60 million years is a measure of absolute time. So is 12:00 pm. These are numerical representations of time, and they give us specific points of reference.
We have a long record of events in absolute time but much of that occurred before humans were on Earth to write it down. So instead of human records, geologists use techniques such as radiometric dating. These processes involve sampling rocks and determining how old they are from their rate of decay.
Relative Time
Since absolute time gives us points of reference, it helps calibrate relative time, also called chronostratic time ('strata' means 'layers'). Here, we are looking at events relative to other events. For example, instead of 12:00 pm we might say 'lunch time.' There is no definitive time for lunch, except that it occurs between breakfast and dinner. So relative to the other meals, it falls in the middle and is later than breakfast yet earlier than dinner.
This is useful in geology because you can age layers of rock relative to other layers. But instead of saying that one layer is x number of years old, you can simply describe it as older than the layer above it yet younger than the layer below it. Relative age starts from the bottom and works upward.
Geologic Time Scale
Rock ages, both absolute and relative, are useful because the rocks represent events in Earth's history such as the age of fossils or major geologic events like meteors and volcanic eruptions. And when we put both absolute and relative time together, we create a geologic time scale that puts all these events in perspective. On this scale, periods, eons, epochs, etc. are layered in their relative order from oldest at the bottom to most recent at the top, and we also see how much absolute time each one spans.
![]() |
For example, if we look at the scale, we see that the Paleozoic Era comes before the Mesozoic Era, relatively speaking, and that it spans about 290 million years, starting about 542 million years ago and ending about 251 million years ago.
Lesson Summary
Both relative and absolute time are important ways we describe events in Earth's history. Absolute time, also called chronometric time, gives us distinct measurements and points of reference, such as 65 million years ago or 5 pm. We get these rock dates and ages with radiometric dating techniques that tell us how old rocks are based on their rate of decay.
Relative time, also called chronostratic time tells us when events occurred relative to each other. For example, a rock layer that is below another one is older, and we know this even without knowing how old the rocks are simply by their position relative to each other. Just like we know that dinner comes after lunch even though we may not know what time it occurs.
When we put both absolute and relative time together, we create a geologic time scale. Rocks relate to events in Earth's history, and we can use them to put together a timeline that shows us both the order of events as well as when and for how long they occurred.
To unlock this lesson you must be a Study.com Member.
Create your account
Register to view this lesson
Unlock Your Education
See for yourself why 30 million people use Study.com
Become a Study.com member and start learning now.
Become a MemberAlready a member? Log In
BackResources created by teachers for teachers
I would definitely recommend Study.com to my colleagues. It’s like a teacher waved a magic wand and did the work for me. I feel like it’s a lifeline.
Relative vs. Absolute Time in Geology
Related Study Materials
- Earth Science for Teachers: Professional Development
- Anatomy & Physiology for Teachers: Professional Development
- General Chemistry for Teachers: Professional Development
- Environment & Humanity for Teachers: Professional Development
- Physical Geology for Teachers: Professional Development
- CLEP Biology: Study Guide & Test Prep
- UExcel Anatomy & Physiology: Study Guide & Test Prep
- NY Regents Exam - Living Environment: Tutoring Solution
- Middle School Earth Science: Help and Review
- Middle School Life Science: Tutoring Solution
- AP Biology: Tutoring Solution
- ILTS Science - Physics (116): Test Practice and Study Guide
- Introduction to Natural Sciences: Certificate Program
- Supplemental Science: Study Aid
- Biology 101: Intro to Biology
Browse by Courses
- Absolute Age: Definition & Dating
- Numerical and Relative Geological Dating
- Period Bibliography: Definition & Examples
- Cell Division in Prokaryotes
- What is a Nerve Net?
- What is Basal Body Temperature? - Definition & Examples
- What is Calmodulin? - Definition & Structure
- How is Calmodulin Activated? - Pathway & Function
- Foundations of Science: Homeschool Assignment
- Atomic Models: Homeschool Assignment
- What is Desorption? - Definition & Process
- What is Thermal Desorption? - Technology & Analysis
- Adsorption Chromatography: Applications & Types
- Adsorption: Definition & Examples
- Adsorption: Uses & Importance
Browse by Lessons
Explore our library of over 84,000 lessons
- Create a Goal
- Create custom courses
- Get your questions answered