unit 2 (dating)

Earth’s physical features were formed by sudden unexplainable events

the geologic processes at work today were also active in the past

places events in a sequence of events, cannot tell us how long ago something happened, only that it followed one event and preceded another

identifies the actual date of an event

in any undisturbed sequence of sedimentary rocks, a sedimentary layer is older than the layers above it and younger than the ones below it

most layers of sediment are deposited in a horizontal position, and if they aren’t, they were moved into that position later

igneous rock is younger than the rocks it has cut across

pieces of one rock found in another rock must be older than the rock in which they are found

in a stratigraphic sequence, different fossils appear in a definite order. Once a species disappears it will never reappear higher in the sequence

buried eroded surfaces which represent gaps in geologic time.

compressional forces cause layers to fold as they uplift

rock layers above and below the eroded surface area parallel

eroded surface of metamorphic or igneous layers are buried by younger sedimentary layers

when sedimentary rocks are compressed and bend into wave like patterns

crack in the Earth’s surface along which movement occurs

when molten rock comes into contact with older rock the heat causes a kind of baking that changes the older rock

a radioactive sample is the parent material, and the decayed product is called the daughter material.

chemical element

remains of organisms found in sedimentary rocks

the rate at which a radioactive element decays

age of rocks and the environment in which rocks are formed

fine sediment encloses delicate matter in an oxygen poor environment. Over time, pressure squeezes out remnants,leaving behind a thin residue of carbon

rapid burial (scavengers/decomp by bacteria) presense of hard body parts low oxygen environment (decomp is slower)

organisms buried in sediment then dissolved, leaving an impression