1. Radiometric Dating: This is the most common and reliable method. It relies on the predictable decay of radioactive isotopes within the rock. Each isotope decays at a specific rate, known as its half-life. By measuring the ratio of the parent isotope to its daughter product, geologists can calculate the time elapsed since the rock crystallized. Common isotopes used include Carbon-14 (for relatively young samples), Uranium-Lead, Potassium-Argon, and Rubidium-Strontium.
2. Relative Dating: This method doesn't provide a numerical age but establishes a sequence of events. Geologists use principles like:
* Superposition: In undisturbed rock layers, the oldest layer is at the bottom, and the youngest is at the top.
* Cross-Cutting Relationships: A rock intrusion or fault is younger than the rocks it cuts through.
* Fossil Succession: Fossils occur in a specific order, and if the same fossil is found in two different rock formations, they are likely the same age.
Relative dating is often used in conjunction with radiometric dating to provide a more complete understanding of the rock's history.
