After two half-lives theres only going to be 25% of the original isotope, 75% of the decay product.
The water flowing in a stream or river is fed by numerous smaller streams, which are fed by even smaller streams that collect water from melting snow or ice up in the mountains, from springs, and possibly from human wasterwater sources. The bottoms of rivers are also below the water table in many places, so there will always be water at that level.
<span>They move from west to east by the Prevailing Westerlies and Jet Streams</span>
Answer:
the arow in the up is the east