The graph below shows the radioactive decay of potassium whose half life is 1.25 billion years.

graph with amount of radioactive potassium present (in grams) plotted on y axis and number of half-lives plotted on x axis. the points (0, 1000), (1, 500), (2, 250), (3, 125), and (4, 62.5) have been joined using a smooth curve.

in your own words, summarize the information provided by the graph about the radioactive decay of potassium.