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Geologic Time
Cha[p 13 and 14
Question | Answer |
---|---|
Geologic time is divided into units based on? | organisms |
The longest subdivision of geologic time is | eon |
A life-form in Precambrian time | cyanobacteria |
The dinosaur evolved during the _____ era | Mesozoic |
Little is known about the Earth's early history because | Precambrian rocks have been changed by heat and pressure |
Humans first appeared during the ____ era | Cenozoic |
Is measured in half-lifes | radioactive decay |
Preserved animal tracks are called | trace |
An unconformity is a _________of a rock. | missing layer |
Fossils are | remains |
Cavity left in a rock after hard parts have dissolved | Mold |
Fossils up to 75,000 years can be dated with | carbon-14 |
Parts of organisms that are most likely to become fossils | hard |
Preserved animal tracks | trace |
made when sediments fill in the cavity made when an object decayed and the sediments harden into rock | cast |
the order of events and the relative age of rocks is determined by examining the position of rocks in a sequence | relative dating |
the time it takes for half of the atoms in an isotope to decay | half-life |
states that for undisturbed rocks, the oldest rocks are on the bottom and the rocks become younger and younger toward the top | principle of superposition |
states that the Earth's processes today are similar to those that took place in the past | uniformitarianism |
the process of calculating the absolute age of rock by measuring the amounts of parent and daughter materials in a rock and by knowing the half-life of the parent | radiometric dating |