Answer:A useful index fossil must be distinctive or easily recognizable, abundant, and have a wide geographic distribution and a short range through time. Index fossils are the basis for defining boundaries in the geologic time scale and for the correlation of strata.
There is no much important of earth crust in human beings but for the people who r trying to be the scientist or discovers need to learn about it
Two that I know of are a sextant, and maybe an astrolabe
<span>c. the thermostat, which controls the temperature in the house, broke last night.
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