Absolute Dating Techniques

Absolute Dating

• Absolute-age dating is a technique used to determine the numerical age of rocks and other materials.
• Radioactive isotopes are used to determine the absolute age of rocks and other materials.
• Radioactive decay occurs at a constant rate as radioactive isotopes emit atomic particles.

Determining Absolute Age

• The original radioactive isotope (parent) is gradually converted into a different element (daughter) as the number of protons changes with each emission.
• Examples of parent-daughter pairs include Uranium-238 to Lead-206, Uranium-234 to Thorium-230, and so on (as shown diagrammatically)

Half-life

• Half-life is the time it takes for one-half of the original isotope to decay into a stable form.
• After one half-life, a sample contains 50% parent and 50% daughter isotopes.
• After two half-lives, a sample contains 25% parent and 75% daughter isotopes.

Radiometric Dating

• Radiometric dating is a technique where scientists use the ratio of parent to daughter atoms to determine the absolute age of a material.
• A decay curve for a radioactive element depicts the percentage of parent atoms remaining over time.
• A growth curve for a daughter product demonstrates the percentage of daughter atoms forming over time.

Radiocarbon Dating

• Radiocarbon dating uses Carbon-14 to determine the age of organic materials (like fossils).
• Carbon-14 is a radioactive isotope of Carbon.

Aging Rocks

• Igneous and metamorphic rocks are dated using radiometric dating, analyzing the parent-daughter ratios of radioactive isotopes present in the minerals.
• Sedimentary rocks are dated by examining layers of igneous or volcanic ash above and below the sedimentary layers.

Alternative Absolute Dating Methods

• Dendrochronology uses tree rings to determine absolute age, with ring width correlated with environmental conditions.
• Ice-core chronologies study glacial cycles.
• Varves are alternating light and dark-colored sediments, useful for geologic history investigations.

Fossil Remains

• Fossils are the remains or traces of past life and provide information about extinct species.
• Evolution is the change in species over time, as seen in the fossil record.

Formation of Fossils

• Fossils with original preservation show little alteration since the organism's death.
• Soft organic materials typically decay quickly, leaving behind hard parts like shells, bones or cell walls.
• Fossils can include molds (formed when sediments cover and then remove the hard part), casts (formed when the mold fills with a different material), and trace fossils (indicating how an organism lived, moved, obtained food: footprints, worm trails, etc).