How did the discovery of radioactivity enable the direct measurement of deep time?

Ateam of scientists studied the sediment at the bottom of an ancient lake. they were able to determine the weather conditions of the indus valley in ancient times. they found that the entire area had suffered a drought after the monsoons declined. this drought lasted 200 years. because of the drought, there wasn’t enough food or water. the people of the indus valley were forced to leave their cities.

What do you think was a drawback to this method of calculating distance

It can be inferred that the dramatic increase in defense spending by germany was the result of. (a) attempts by great britain to take german colonies. ( b) fear of a two-front war against france and russia (c) the need to put down a communist rebellion (d) a competition with the allies to produce atomic weapons