Radioactive decay of 40k atoms in an igneous
rock has resulted in a ratio of 25 percent 40k
atoms to 75 percent 40ar and 40ca atoms.
how many years old is this rock?
(1) 0.3 10^9 y (3) 2.6 10^9 y
(2) 1.3 10^9 y (4) 3.9 10^9 y

The red square is a famous historical site that is located in

The model of human settlement suggests that uthe model of human settlement suggests that urban growth is patterned around transportation networks such as railroads and highways. a. burgess b. hoyt c. sauer d. von thunenrban growth is patterned around transportation networks

Most of earths fresh surface water is found in