1) A thin unique layer in the rock record is used as a marker of rocks a) superposition b) fossils c) geologist d) key bed 2) What unit of time is used in Earth's time scale a) billions of years b) millions of years c) trillion years d) hundreds years 3) An index fossil is the fossil of an organism that lived for a short time, Which fossils are index fossils.  a) horseshoe crab b) ammonites c) coelacanths 4) in the figure the ash layers are dating as shown , what conclusion can you draw about the ages of the layers? a) the layer above the top ash layer is 540 mya b) the layer above the top ash layer is younger than 540 mya c) the layer between the two ash layers is younger than 540 mya 5) When almost all living organisms die in a short time this is called ....... a) key bed b) index fossil c) mass extinction 6) iridium element found in a high percentage on earth but very rare on meteorites a) true b) false 7) would you expect to find a dinosaur fossil above the iridium layer? (rare on Earth but common on meteorites,)  a) yes, as dinosaurs died because of meteorites b) yes, as iridium is a poisonous element c) no , the layer above iridium is younger and marks mass extinction by meterites

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