Earth recycles 2.5-billion-year-old ocean crust  April 24, 2013
at 5:28 PM ET  J.M.D. Day / A cross-polarized light image of the
lava sample from Mangaia island, showing sulfide grains in the
rock at 1.5 times magnification.  By Becky Oskin   The remains
of a real-life journey to the center of the Earth are preserved
in a South Pacific volcano, a new study suggests.  The lava that
erupted from the Cook Islands volcano, called Mangaia, contains
a few tiny grains of sulfide, a mineral, with a peculiar ratio
of sulfur isotopes, according to research published in
Wednesday's issue of the journal Nature. The unusual ratio could
only have formed before oxygen-breathing life appeared on Earth
2.45 billion years ago. Isotopes are versions of elements with
different numbers of neutrons, giving them differing weights.
The study researchers think the sulfide formed at Earth's
surface ages ago in ancient oceanic crust, and then sank deep
into Earth's mantle, likely all the way to the core-mantle
boundary, 1,865 miles (3