Geoscience Reference
In-Depth Information
9
'Formed stones' and
their subsequent role
in biostratigraphy and
evolutionary theory
Fossils are the remains of plants and animals that are preserved in
rock. The oldest evidence for life comes from carbon found in rocks on
the island of Akilia in southern Greenland that have been dated as
being 3,850 million years old. Some authorities have argued that this
date is inflated, and that the rocks are in fact 150 to 200 million years
younger. Worse still, they have been interpreted as being a banded
ironstone, which would indicate that the carbon was not organic. The
oldest undisputed fossils are thought to be blue-green algal filaments
found in the Apex chert inWestern Australia, which are 3,465 million
years old. For many millennia, fossils have been the focus of curiosity,
but only in the past 150 years have fossils been systematically studied
and described. They are useful tools in dating the geological past and
have also been used to correlate sequences of rock from area to area,
locally or even fromcontinent to continent. The discipline of studying
fossils is called palaeontology.
Our understanding of what fossils are and what they can tell us
is continually evolving. This is what makes the subject so interesting.
Research on fossils is always changing and newmethodologies appear
every year to test new ideas or re-evaluate old hypotheses. Twenty
years ago, it was unheard of to use sophisticated instruments such as
mass spectrometers to measure the ratios of the various oxygen iso-
topes trapped within fossil skeletons, which yield information about
the temperature of the sea water from which the skeleton was pre-
cipitated. Today, it is commonplace. We are interested in discovering
if we can determine how animals reacted in the past to small vari-
ations in climate and deduce the implications for present-day life.
