Essential Vocabulary and Questions I can determine the relative age of rocks based on fossil evidence. I can interpret the existence of disturbances in sedimentary rock layers. What is a fossil? (pg 81) Fossil – the trace or remains of an organism that lived long ago (fossils are formed from hard tissues like bone, not skin) - Fossils are most often found in SEDIMENTARY ROCK layers. - Older rocks tend to contain fossils of organisms that are more simple than those alive today. What is an index fossil? (pg 114-
115) Index fossil (pg 114) – fossils that are used to estimate the absolute age of the rock layers in which they are found. Which layer of rock was put down first? - To be an index fossil, a fossil must: 1) Only live during a short period of Which fossil is the oldest (you can describe time. what it looks like if you don’t know the name)? 2) Be relatively common 3) Be found over a large area TEST YOURSELF! If a fossil is found in a layer of rock in America and scientists know that it is 100 million years old, if the same fossil is found in another country far away, using index fossils, how old can we say that rock layer is? -‐ o 100 million years old I can determine the relative age of rocks based on fossil evidence. I can interpret the existence of disturbances in sedimentary rock layers. How are undisturbed and disturbed rock layers dated? Law of Superposition (pg 95) - the principle that states that younger rocks lie above older rocks if the layers haven’t been disturbed. YOUNGER ---------------------------------- OVER ---------------------------------- OLDER How are sedimentary rock layers disturbed? (pg 96) ALL EVENTS HAPPEN AFTER ROCK LAYERS ARE FORMED! Tilting – when Earth’s forces move rock layers up and down unevenly Folding – the bending of rocks that can happen when rock layers are squeezed Faults – a break or crack in Earth’s crust where rocks can move Intrusion – igneous rock that forms when magma is injected into rock and then cools and becomes hard. Extrusion – a layer of hardened horizontal, igneous rock Unconformity – a break in the geologic record that is made when rock layers are eroded or when sediment is not deposited for a long time. Draw an unconformity below. I can determine the relative age of rocks based on fossil evidence. I can interpret the existence of disturbances in sedimentary rock layers. What is the difference between relative and absolute dating? Geologic time scale (pg 122) - The life forms and geologic events in Earth’s history - The Earth is 4.6 Billion years old! What is relative dating? (pg 94) Relative dating - a rock’s age compared to the ages of other rocks. (YOUNGER OVER OLDER) How can the absolute age of a rock be determined? (page 108) Absolute dating – determining the actual age of an event or object in years (see the box on the right) Radiometric dating – a process that enables geologists to determine the absolute ages of rocks. (see the box on the right) 0 years have passed How do geologists find the exact age of rocks? (pg 108-109) Atom – contain proton (+), electrons (-‐) and neutrons (0) Atoms want to have the same amount of protons and neutrons to be stable (they want to be stable!) Isotope – atoms of the same element, but with different numbers of neutrons  Some isotopes are unstable (radioactive) and break down into a different isotope to be stable. Parent isotope – radioactive isotope that decays Daughter isotope – the more stable isotope the parent isotope decays into. Half-life (pg 109) – the time needed for 1/2 of the parent isotopes to decay into daughter isotopes (ALWAYS A SET AMOUNT OF TIME) After 1 half-life