Travel Reference
In-Depth Information
In the decades following this monumental discovery, thousands of sci-
entific papers appeared detailing the tesults of oxygen isotope analyses of an-
cient temperature. Soon a rough, and then an increasingly more precise, pic-
ture emerged of global sea temperature through time. The most neatly
continuous record of variation in marine temperature over the past 100 mil-
lion years has come from isotopic analyses of well-preserved foraminiferans
(single-celled protist shells) recovered from deep sea cores.
There were many caveats, of course. It did no good to compare the av-
erage bottom temperature (as measured from shells of bottom-dwelling crea-
tures) and the average temperature of surface water (as measuted from
shells of planktonic creatures, which live mainly at the sea's surface), be-
cause bottom water is always much colder than that at the surface. But
when similar sorts of comparative analyses were made, a quite detailed pic-
ture emerged.
The result of this work was to show that the temperature of the sea has
clearly fluctuated. The two warmest periods of the last 100 million years were
during the Late Cretaceous (about the time when the rocks that now make
up Sucia were deposited) and during the 50-million-year-old Eocene Epoch.
The world's oceans appear to have been appreciably warmer during these
two times than they are now, even in high-latitude seas.
Many measurements of a variety of mollusk shells were made unevent-
fully, but when scientists began measuring the temperature of inoceramid
shell material, they got a profound shock. The temperatures found in these
shells were always very high compared to those of other shells in the same
deposits. Inoceramid shells from Sucia Island, for example, yielded a temper-
atute of 95°F! The only places on earth whete one finds such hot sea water
are right at the surface at the equator and in restricted lagoons and salt
marshes. Sucia was tropical, though not that tropical, according to most in-
dicators. Analysis of the other clams and shells from Sucia suggested that its
sediments were deposited in fairly shallow water, perhaps 50 to 100 feet deep
at most. Perhaps—just possibly—the water could have been that warm.
But a greater surprise was yet in store. Isotopic analyses of inoceramid
shells collected from very deep-water sediment showed similarly high readings.
