Atoms of A decay to atoms of B with a half-life of 200,000 years. If there are 20,000 atoms of A to begin with, how long will it take for there to be 2,500 atoms of A?

The correct answer is: 600,000 years

Explanation:

Half-life is the time which is essential or required to decrease a specific substance to half of its initial amount of the substance. So, if a substance has a half-life of 200,000 years then it means it takes 200,000 years to decrease or change into a new substance and remain half of its initial quantity.

half-life              amount

     0                  20000

     1                    10000          

     2                    5000

     3                     2500

total half-life = 3 to 2500 atoms of A

so, the time will be = 3 * 200,000 years

 = 6000000

he movement of air through earth's or any planet's atmosphere is called wind, and the main cause of earth's winds is uneven heating by the sun. this uneven heating causes changes of atmospheric pressure, and winds blow from regions with high pressure to those with low pressure.

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c. earths continental crust is thicker than its lithosphere.

because, the lithosphere is the outermost layer of the earth/ 100 km thick and is defined by its machanical properties.the lithosphere contains oceanic and continental crust that varies in age and thickness across locations and geologic time. the lithosphere is the coolest layer of the earth in terms of temperature. the term lithosphere should not be confused with the use of "geosphere" which is used to indicate all of earth systems, including the atmosphere, hydrosphere   and biosphere. the surface of the earth can be divided into the continental crust and the oceanic crust.   the continental crust is made mostly of granite while the oceanic crust is made of basalt. the average thickness of the continental crust is 25 miles and the average thickness of the oceanic crust is 5 miles.   three types of rock, igneous, sedimentary, and metamorphic, make up the surface of the earth. that's why 3 option is preferable.