Earth’s Geological History

Geological Time Scale What does this tell you? What do the breaks represent?

Index Fossils What are they? Found in a narrow time range but was widely distributed around the earth Used to date rock layers example: trilobite

Unconformity Gaps in the rock record Types – Angular-older layers dip at a different angle then the younger layers – Disconformity-rock layers are parallel – Nonconformity (heterolithic)- younger rock rest nonparallel to older rock layers – Local unconformity-stritcly limited and represents a short period

Absolute Dating vs. Relative Dating Absolute- – Any method of measuring the age of an event or object in years Actual age for a rock or mineral Relative- – Uses information about rock layers and the fossil record to determine the age relationships between rocks Putting layers in order

Absolute Methods Radiometric dating uses Radioactive decay – Process in which a radioactive isotope tends to break down into a stable isotope of the same element or another element REMEMBER isotope-atom with same number of protons as other atoms of same element but different amount of nuetrons (different mass) Half-life- amount of time needed for half of the sample to decay

Relative Dating Methods Law of Superposition – Oldest rocks lie on the bottom and the youngest rocks are on top of any undisturbed sequence of sedimentary rocks

Plate Tectonics The theory that explains how large pieces of the earth’s outermost layer called tectonic plates move and change shape. – Explained by the theory of continental drift: gradual shifting of earth’s plates causes continents to change their global positions over time. Evidence: – Fossil record – Matching coastlines – Index fossils

Plate Boundaries Divergent Boundary- Where two plates are moving apart – Evidence Deep ocean trenches Convergent Boundary- Where two plates are moving together – Evidence Mountain Ranges