Relative and Absolute Dating

Remember the Fossil Record? The fossil record gives important information about past life and environments on Earth. Certain fossilized organisms could only live in specific environments or under particular climate conditions.

Relative Dating Relative dating allows scientists to infer the relative age of a fossil. Relative age does not tell the exact age of a fossil! The relative age can be determined in one of two ways: Ordering of Rock Layers Using index fossils

Ordering of Rock Layers Scientists use the Law of Superposition to understand rock layer ordering. The Law of Superposition: each rock layer is older than the one above it This is used to read rock layers. Scientists use this law to figure out the relative age of a rock or fossil.

Index Fossils Lets use the trilobite as an example of an index fossil… Trilobites are hard-shelled animals They lived in shallow seas They became extinct about 245 million years ago

Index Fossil So with that in mind if a trilobite is found in a specific rock layer scientists can estimate that those rocks and fossils below it are OLDER and those found above it are YOUNGER.

Absolute Dating Geologists use radiometric dating to estimate the exact age of an object.

How can the absolute age of rock be determined? Radioactive atoms will decay over time. Parent atoms will decay into “daughter atoms” Half-life is the time needed for half of a sample of a radioactive element to decay and form daughter isotopes The atoms will decay at a predictable rate, so scientists will compare the number of unstable to stable atoms to figure out the absolute age of an object.

Carbon 14 Dating Certain chemical elements have more than one type of atom. Different atoms of the same element are called isotopes. Carbon has three main isotopes. They are carbon-12, carbon-13 and carbon-14. Carbon-12 makes up 99% of an atom, carbon-13 makes up 1% and carbon-14 - makes up 1 part per million. Carbon-14 is radioactive and it is this radioactivity which is used to measure age.

Carbon 14 Dating By counting how many carbon-14 atoms in any object with carbon in it, we can work out how old the object is - or how long ago it died. So we only have to know two things, the half-life of carbon-14 and how many carbon-14 atoms the object had before it died. The half-life of carbon-14 is 5,730 years.