Life on Earth might never have happened without some well-placed
rocks  Biologically speaking, it isn't that hard to create very
simple, one-celled organisms. But the leap to multicellular life
requires many factors to line up just perfectly. Now a new
hypothesis suggests we wouldn't even be here without some well-
timed erosion.  Certain proteins seem to be essential for the
rise of multicellular organisms, and those proteins require
ready access to heavy-metal elements like zinc and copper.
That's no problem these days, but these heavy-metal elements
spent a couple billion years of Earth's early history locked
away where organisms couldn't get access to them, and the
absence of these elements likely held our earliest ancestors'
evolutionary path in stasis, unable to make the big leap to
being multicellular.  Exactly where those elements were has long
been a big question for geologists, with previous explanations
looking at the oxygen-starved ocean depths and ore deposits in
the Earth's crust as likely storag