Biology Reference
In-Depth Information
pioneered by Harold Urey and Cesare Emiliani; sea level curves constructed
by Peter Vail and Jan Hardenbol using Exxon's worldwide database on
coastal sediments; phylogenies incorporating chemical profi ling advocated
and early demonstrated by Ralph Alston and B. L. Turner; and a temporal
context provided by relative age and the absolute dating techniques devel-
oped by J. A. Arnold, W. F. Libby, Harold Urey, and others (see chap. 3).
Modern plant and animal communities are among the most complicated
assemblages ever to occupy the planet, but fortunately, it is also a time when
an impressive arsenal of innovative approaches is available for tracing their
history. Consider, for example, what it is now possible to do:
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Reconstruct changes in the atmospheric concentration of CO
2
, methane,
and other greenhouse gases over the past 100 million years from the ex-
tent of carbonate and other sediments (e.g., limestone, CaCO
3
) and from
air bubbles trapped in glacial ice.
Trace marine paleotemperatures and terrestrial ice volumes over a similar
period from oxygen isotope ratios and, by extrapolation, the ancient
temperatures of coastal and terrestrial habitats in conjunction with the
fossil record.
Detect fl uctuations in the amount of heat reaching the Earth's surface
over time owing to changes in the planet's position relative to the sun
(Milankovitch variations).
Estimate the paleoaltitude of mountains at different stages in their history
from the MAT of fossil fl oras deposited at sea level, and others at high
elevations, then use the worldwide average lapse rate of about 6°C/km to
calculate the original altitude of the higher fl ora.
Trace rainfall patterns from the width of growth rings in stalactites, and
from the ecology of mites and midges often preserved in them.
Reconstruct paleotemperatures from amino acid racemization of fossil
Emu
eggshells. Racemization is the change from levorotatory—rotating
polarized light to the left—to a mixture of levorotatory and dextrorotatory
forms of a molecule, and the rate of change is a function of temperature.
Detect the change from cold glacial to warmer postglacial climates (e.g.,
in central Alaska between 12,000 and 10,500 BCE) by the ecology of
beetle species preserved in lake sediments.
Track the temperature record of marine waters over time from long-chain
organic molecules called alkenones preserved in ocean sediments as
biochemical fossils. The relative abundance and degree of saturation is
temperature dependent: increasing unsaturation indicates cooling water.
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