Page 36 - Introduction to Paleobiology and The Fossil Record

FOSSILS IN TIME AND SPACE 23
The Earth is immensely old, and the distribu-
tion of continents and oceans has changed
radically over time. Early paleontologists did
not know these things, and so they tried to
pack the whole of the history of life into a
relatively short span of time, vizualizing trilo- in both temporal and spatial frameworks. It
bites or dinosaurs inhabiting a world that was
much as it is today.
Life on Earth, however, has been evolving
for up to 4 billion years, and there has been a
complex story of fossil groups coming and
going, and continents moving from place to
place. How do we develop geographic and
temporal frameworks that are accurate and
reliable enough to chart the distributions of
fossil organisms through time and space? For-
tunately, paleogeographers and stratigraphers
are now equipped with a range of high-tech
methods, virtually all computer-based, that
provide a greater consensus for models describ- rocks are overlain by younger rocks if the
ing the distributions of the continents, oceans
and their biotas throughout geological time.
Fossils also store information on the fi nite
strain and thermal maturation of rocks located
in the planet’s mountain belts, allowing the
tectonic history of these ranges to be recon-
structed; thermal maturation information is
important in identifying the levels of thermal
maturity of rocks and the gas and oil windows
in hydrocarbon exploration. In some cases
fossil shells also contain isotopes and other
geochemical information that can identify
changes in global climate (see p. 111).
FRAMEWORKS
Six distinct aspects of Tuscany we there-
fore recognize, two when it was fl uid,
two when level and dry, two when it was
broken; and as I prove this fact concern-
ing Tuscany by inference from many
places examined by me, so do I affi rm it
with reference to the entire earth, from
the descriptions of different places con-
tributed by different writers.
Nicolaus Steno (1669) The
Prodromus of Nicolaus Steno’s
Dissertation Concerning a Solid Body
Enclosed by Process of Nature
Within a Solid
Before the distributions of fossils in time
and space can be described, analyzed and
interpreted, fossil animals and plants must be
described in their stratigraphic context. A
rock stratigraphy is the essential framework
that geologists and particularly paleontolo-
gists use to accurately locate fossil collections
seems, not surprisingly, that like a fi ne bottle
of Italian wine, this can be traced back to the
sunny, pastel landscapes of Tuscany and the
Renaissance.
Leonardo’s legacy
The origin of modern stratigraphy can be
traced back to Leonardo da Vinci and his
drawings. Pioneer work by the Danish poly-
math Nicolaus Steno (Niels Stensen) in north-
ern Italy, during the late 17th century (see
p. 11), established the simple fact that older
sequence has not been inverted (Fig. 2.1a).
His law of superposition of strata is funda-
mental to all stratigraphic studies. In addi-
tion, Steno established in experiments that
sediments are deposited horizontally and
rock units can be traced laterally, often for
considerable distances; remarkably simple
concepts to us now, but earth shattering at
the time. But what has this got to do with
da Vinci?
Leonardo da Vinci (1452–1519) is famous
for many things, and his contributions to
science are refreshingly modern when we look
back at them. In his art, da Vinci essentially
rediscovered geological perspective, some 200
years before Steno, during the Renaissance
(Rosenberg 2001). In his drawing of the hills
of Tuscany, da Vinci portrayed a clear sequence
of laterally-continuous, horizontal strata dis-
playing the concept of superposition. More-
over, about a century after Steno, Giovanni
Arduino recognized, again using superposi-
tion, three basically different rocks suites in
the Italian part of the Alpine belt. A crystal-
line basement of older rocks, deformed during
the Late Paleozoic Variscan orogeny, was
overlain unconformably by mainly Mesozoic
limestones deformed later during the Alpine
orogeny; these in turn were overlain uncon-
formably by poorly consolidated clastic rocks,
mainly conglomerates. These three units con-
stituted his primary, secondary and tertiary
systems; the last term has been retained and
formalized for the period of geological time