Fossil Dating

HOW DO WE KNOW THE AGE OF FOSSILS? Scientists use 2 methods to determine the age of fossils: 1. Relative Dating 2. Absolute Dating

Relative Dating Shows the order in which fossils occurred- does not give exact ages. Shows what organisms lived together. Scientists look at where fossils are located within the rock column. Use the Law of Superposition

Relative Dating…

Law of Superposition Sedimentary layers are deposited in a time sequence Oldest rock on the bottom, youngest at the top

Absolute Dating Determines the specific age of a fossil Looks at chemical properties 2 types: Carbon-14 (radiocarbon) Potassium-Argon

Carbon-14 Dating Also known as Radiocarbon dating Used to date organic substances Scientists measure the radiocarbon in the fossil to determine its age. Carbon- 14 decays at a predictable rate. You must know starting point of Carbon 14 to figure age. Can only date specimens up to about 60,000 years old

Potassium-Argon Dating Scientists determine the age of the rock surrounding the fossil to determine the fossil’s age. Used only for inorganic substances (rocks and minerals) Scientists measure the amount of argon in the rock to determine its age (Potassium decays into Argon) Dates rock 60,000 years old and older

QUIZ

Which rock layer is the oldest? Youngest?

If you wanted to figure out the exact age of a rock, what technique would you use? Relative Dating Carbon-14 Dating Law of Superposition Potassium-Argon Dating

If you were looking to find the exact age of a fossil that is at least 1 million years old, what technique would you use? a. Carbon-14 Dating b. Potassium-Argon Dating c. Relative Dating d. You can’t; it is impossible

If you wanted to figure out the exact age of a fossil that is less than 40,000 years old, what technique would you use? a. Carbon-14 Dating b. Potassium-Argon Dating c. Relative Dating d. You can’t; it is impossible