Age of Rocks Standard Infer the relative age of rocks and fossils from index fossils and the ordering of rock layers.

Index Fossil EQ: How can the relative age of rocks and fossils be inferred from index fossils?

Relative Age What is relative age? The age of rocks & fossils can be determined using what two basic methods? the age of one object compared to the age of another object does not tell the exact age of an object ordering of rock layers & index fossils

Index Fossils What are index fossil used for? To be an index fossil the organism: to help find the relative age of rock layers. 1. must have lived only for a short part of Earth’s history 2. must be unique 3. many fossils of the organism must be found in rock layers: abundant 4. the fossil must be found over a wide area of Earth

Trilobite What makes for a good index fossil? What is a trilobite? the shorter time period a species lived, the better the index fossil-trilobite is a key example a hard-shelled animal whose body had three (3) sections lived in shallow seas became extinct about 245 million years ago

Helpful Trilobites How can you estimate the age of the layer in which a trilobite is found? What is NOT an index fossil? if a trilobite is found in a particular rock layer, it can be compared with trilobites from other rock layers fossils are found in many rock layers, therefore living long periods of time, does NOT qualify other organisms as index fossils

Ordering of Rock Layers EQ: How can the relative age of rocks and fossils be inferred from the ordering of rock layers?

Ordering of Rock Layers strata: How do scientists “read” rock layers? rock layers each rock layer is deposited on top of another rock layer

Law of Superposition What does the law of superposition state? states that each rock layer is older than the one above it the relative age of the rock or fossil in the rock is older if farther down in the rock layers this relative dating can be used only when the rock layers have been preserved in their original sequence