Britannica
Sources used in this answer
How does paleomagnetism provide another way to build a geologic time scale?
Created from Britannica articles
using AI.
AI can make mistakes, so verify using Britannica articles.
geochronology
The steep walls of the Grand Canyon contain a number of layers of sedimentary rock laid down over millions of years. The lower formations belong to the early Precambrian age, while the upper layers are of the Paleozoic age. The line between the two sets of formations is called the Great Unconformity.
Paleomagnetism provides a vital method for constructing a geologic time scale by utilizing the record of Earth’s magnetic field reversals preserved in rocks.12
As igneous and sedimentary rocks form, magnetic minerals within them align with and "lock in" the ambient magnetic polarity of the time. Because the Earth's magnetic polarity has reversed periodically throughout history, these rocks create a chronological sequence of "normal" and "reversed" intervals.132
This process contributes to geochronology in several ways:
- Marine Magnetic Anomalies: As seafloor spreading occurs, new oceanic crust records these reversals as linear magnetic anomalies parallel to ridge crests. By mapping these patterns and calibrating them with radioisotopic dating, scientists can determine the age of the seafloor and reconstruct spreading history.32
- Magnetostratigraphy: By measuring the magnetic orientation in strata and deep-sea cores, researchers can establish a paleomagnetic chronology.12
- Integrated Time Scales: A robust geologic time scale is derived by integrating these magnetic polarity successions with biostratigraphy and isotopic ages, allowing for high-resolution dating of Earth's history.2