Archbishop Ussher took the genealogies of Genesis, assuming they were complete, and calculated all the years to arrive at a date for the creation of the earth on Sunday, October 23, 4004 B. Of course, even assuming the method was valid, such an exact date is not possible from the genealogies of the Bible (Ussher assumed all the years the patriarchs lived were exactly 365.25 days long and that they all died the day before their next birthday).
Nuclear medicine uses radiation to provide information about the functioning of a person's specific organs, or to treat disease.
To do this lesson and understand half-life and rates of radioactive decay, students should understand ratios and the multiplication of fractions, and be somewhat comfortable with probability.
Games with manipulative or computer simulations should help them in getting the idea of how a constant proportional rate of decay is consistent with declining measures that only gradually approach zero.
The photo above is not to make you feel insignificant, it is only for reference and scale. Depending on your field of view, you would have to be around 100,000 light years away to see this Galaxy using the naked human eye.
And as you got closer, it would almost disappear because of the tremendous amount of space there is between everything, like with atoms.