Travel Reference
In-Depth Information
There was no possibility that these large inoceramids, such as the forms on
Gabriola Island, lived in such shallow water. Unless . . .
Unless the giant clams did not live on the cold bottom at all but fell
there only after death. In the 1980s a new hypothesis was proposed: Inoce-
ramid bivalves were attached to floating logs, and all those found in various
deep-water deposits had arrived there only after they died. There seemed to
be no other way to explain the isotopic results, and many serious scientists
subscribed to the "floating inoceramus" theory.
In the late 1980s, two of my graduate students advanced another idea.
In a paper published in the journal
Geology,
Ken MacLeod and Kathryn
Hoppe, after analyzing inoceramid shells collected from deep-water cores in
Europe, suggested that the inoceramids formed their shells in a way that ex-
cluded the isotope oxygen-18. This led to spurious results when the values
were converted to temperatutes using the methods of Urey. The inoceramids
were not living in 95°F water, but their shells wete painting that picture
through what was described as a "vital effect."
Such vital effects were not unprecedented. They are also known from
living corals, which harbor a tiny plant in their flesh that aids in formation
of the skeleton. The presence of this microscopic alga in the coral's flesh also
reduces the amount of oxygen-18 incorporated into the coral's skeleton, and
this yields an anomalously high paleotemperature reading. Yet corals live
only in very shallow seas, for the symbiotic algas in their flesh need warm
water and light. The deep-water inoceramids could not possibly be harboring
such shallow-living symbionts. Something else had to be involved.
Hydrothermal vents and "cold seeps"
The answet came from a completely chance discovery: that of hydrothermal
vent faunas in the modern-day deep sea. On February 17, 1977, the sub-
mersible ALVIN was diving on a mid-ocean ridge deep in the Pacific Ocean.
These are the regions where new sea floor is produced. Oceanographer
Tjeerd van Andel, who was on this historic dive, described the discovery as
follows:
