Printed from The Discovery of Hydrothermal Vents - 25th Anniversary
CD-ROM ©2002 Woods Hole Oceanographic Institution
EARLY CLUES: Evidence
Seafloor Rocks With Curious Chemistry
Rocks
dredged up from the bottom of the sea also contained telltale clues. Most
rocks from the mid-ocean ridge are black in color, with some white and pale
green crystals. But, in the late 1960s and early 1970s, scientists found
mid-ocean ridge seafloor rocks with unusual shades of green, orange,
and brown.
Scientists figured out why these rocks were different by analyzing the minerals
in the rocks, their crystalline structure, and their chemical composition.
They concluded that the original black rocks had been transformed by chemical
reactions that could only have taken place in the presence of hot water.
Much the way detectives might use clues to reconstruct how a crime occurred,
the scientists figured out how the rocks probably formed. Cold seawater
seeped into cracks in the seafloor and was warmed by heat from below. The
hot water reacted and exchanged chemicals with seafloor rocks. The chemical
reactions changed the minerals in the rocks and added minerals to the seawater.
Because hot fluidlike hot airis lighter and rises, the scientists
predicted that mineral-rich fluids would rise back to the surface and discharge
at the seafloor. They predicted that hydrothermal vents might exist, even
before any had been seen.
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