HELP ASAP PLZ EARTH SPACE SCIENCE
1. An element has a half-life of 30 years. If 1.0 mg of this element decays over a period of 90 years, how many mg of this element would remain?

2. A 2.5 gram sample of a radioactive element was formed in a 1960 explosion of an atomic bomb at Johnson Island in the Pacific Test Site. The half-life of the radioactive element is 28 years. How much of this element will remain after 112 years?

3. An element has a half-life of 29 hours. If 100 mg of the element decays over a period of 58 hours, how many mg of the element will remain?

Need help asap plz !!

1. 0.125mg.

2. 0.15625

3. 25mg

Explanation:

1. In 30 years it will divide in half so in 30 yrs it would be 0.5; 30 years after that (or in 60 years) it would be 0.25; in 30 more or 90 years, it would be 0.125mg. The answer is 0.125mg.

2. 112/28 years = 4 half lives go by.

2.5 /2=1.25

1.25 /2=0.625

0.625 /2=0.3125

0.3125/2=0.15625

0.15625 is the answer

3. 58/29=2 half lives, so:

100/2= 50mg

50/2=25mg

25mg is the answer

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.