Claire Corlett

Fish Food, Fish Tanks, and More
Robert L. Fisher’s Rock Collection

Robert L. Fisher’s Rock Collection

In the 1950s, ocean scientists began using scuba
equipment to observe first-hand the underwater world. Their observations raised questions about ocean ecology that no one had even
thought to ask until seeing the communities in action. But what about scientific observation in
the deepest parts of the ocean where it is impossible to dive? Deep-sea explorers had to find a
different approach. They brought the bottom of the ocean up
to the surface. We starting nearly half a century ago, updated or
modified a method that reputedly was used by
Aristotle 2500 years ago in the Aegean Sea when he was tutoring Alexander and in order to do that work we use a frame, a metal
frame which we can hang from a large wire. But below that metal frame is a chain bag, a metal chain bag, and it is limp and the reason we use a
chain bag is so that if that instrument, that
bag, that box gets hung up on the bottom, what we have
caught in it, won’t dump, clever but very simple. On the deck of the ship, teams emptied
the dredges and sorted the hole into piles of like with like. Only occasionally finding odd sample that
didn’t seem to fit anywhere. They brought the samples back to Scripps and submitted them to a battery of
geochemical tests and analysis but some rocks became part of a special
collection managed by Robert L Fisher, the man who dredged the rocks from the
deep ocean floor. This is a a mid-ocean type basalt, this is something that came to the
seafloor as magma but it bait samples of sediment upon
it. It was that hot and the thing that’s interesting about this
particular thing you see a second coming so to speak. You see
within that tube and rock there was some more magma that came in and made a second approach. This is a similar basalt called a gabbro,
from deeper in the earth’s crust. Fisher took a drill sample from it to
test the velocity of sound through it, useful information for seismic
refraction work. But the pride of the collection is a
pristine sample of peridotite. At the beautiful lot of green, the thing that’s unique about
this and and means it really belongs in the
Smithsonian, this rock is that it’s utterly fresh and little or nothing in it but magnesium and silicate. But the
real value in Fisher’s rock collection is what it told geologists about the
movement of the earth’s tectonic plates. Here in my right hand I’m showing
the oceanic rocks moving down and here in the left hand I have the peridotite from the island arc
lying right above so here, right here, you have seen subduction in action. For the first time in
history, a scientist could actually hold in his
own hands hard evidence that one tectonic plate was diving beneath
another, no scuba gear required.

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