Sandra Rivett, age 12, of Pemberton, British Columbia, for her question:

Were the Great Lakes ever salty?

All the so called fresh water of lakes and rivers has a trace of salty chemicals. You cannot taste it in the water of the Great Lakes, but it is there and it always was. Fresh, unsalted rain water seeps into the ground and joins running streams. When seeping or running water comes into contact with the earth's minerals, it dissolves some of their chemicals    especially the salty ones. Springs and streams empty their slightly salty water into the Great Lakes. This has been going on since the lakes were formed, and they were never saltier then they are today.

For ages, the world's rivers have been emptying their slightly salty waters into the oceans. And the sun has been evaporating water vapor from the surface    leaving the salty chemicals behind. As more dissolved chemicals are added, the sea continues to get saltier and saltier. But lakes remain about the same so long as continuing supplies of water drain into them and out again.