I just thought of an end of the world nightmare scenario. What if bacteria developed the ability to metabolize salt? The bacteria reproduction rate would grow so fast that the oceans would become devoid of salt. The oceans would become freshwater, killing all the species, such as saltwater fish, clams, crabs, and lobster that have evolved to live in saltwater. This would cause a mass extinction of epic proportions.
This is very similar to an occurrence foretold in the New Testament:
New International Version
The second angel poured out his bowl on the sea, and it turned into blood like that of a dead person, and every living thing in the sea died. - Revelation 16:3
