Introduction
For a long time, geology books devoted only a few lines to the history of past climates of our
planet, mostly to establish the deposition framework for the sediments that geologists found on
the continents, the only area of enquiry available to them. Scientists soon realized that the
copious coal deposits of England, Belgium, Northern France, Germany, and Poland resulted
from the fossilization of abundant vegetation facilitated by a warm and humid equatorial
climate that reigned over Western Europe, some 350 million years ago (an illustrated insert in
Chap. 2 volume I provides a diagram of continental drift since 540 Ma). Fifty million years
later, the sediments of these same regions, red sandstone, poor in fossils and associated with
evaporites testify to the replacement of forests by desert areas, dotted with occasional highly
saline lakes, similar to what we currently find in Saharan Africa. Humidity gave way to intense
aridity and we had no idea why. It was not until the discovery of plate tectonics that we
realized that Europe had slowly drifted toward the tropics. This transformation of the face
of the Earth due to tectonics is illustrated through 16 maps in Chap. 2 volume I.
The discovery of glaciations was a revelation for the geologists of the nineteenth century.
A major polemic broke out at the Swiss Society of Natural Sciences in Neuchâtel when, in
1837, its president Louis Agassiz presented his explanation, incredible at the time, for the
presence of gigantic boulders that dot the Jura mountains. He daringly claimed that these
erratic boulders were not the remnants of the Biblical Flood, but rather enormous rocks
transported over long distances by gigantic glaciers which used to cover the high latitudes of
our hemisphere.
The controversy died down quickly, when European and American geologists discovered
traces of glaciers all over the Northern Hemisphere, just as Agassiz imagined. In Europe, as in
North America, mapping of the terminal moraines left behind by glaciers when they melted
showed proof of the presence of gigantic ice caps in a past that seemed distant. especially since
there was no idea how to date them.
As the idea of the Biblical Flood fell out of favor, a new theory, based on astronomical
phenomena, soon appeared. Scientists like Joseph Adhémar and James Croll realized that there
were small, quasi-periodic variations over time in the movement of the Earth around the Sun
and suggested that associated mechanisms could periodically cause glacial advances and
retreats. Finally, it was Milutin Milankovitch, a professor in Belgrade, who would lay the
foundations for a complete mathematical theory of glaciations, the legitimacy of which was
proven when paleoceanographers found the frequencies of orbital parameters reflected in the
isotopic analysis of marine cores. We now know that the last one of these glacial periods
culminated only 20,000 years ago and was preceded by many others.
The great contribution by Milankovitch was to plant a new idea within the scientific
community: Ancient climates are not only of immense curiosity to geologists; they obey the
same physical laws as those governing the current climate.
This intellectual revolution has had far-reaching consequences and has profoundly altered
the approach to the study of ancient climates making paleoclimatology a science with many
links to geology, geochemistry, oceanography, glaciology as well as the approach to the
physical and dynamic dimensions of the climate. The first part of this book describes the
ix
For a long time, geology books devoted only a few lines to the history of past climates of our
planet, mostly to establish the deposition framework for the sediments that geologists found on
the continents, the only area of enquiry available to them. Scientists soon realized that the
copious coal deposits of England, Belgium, Northern France, Germany, and Poland resulted
from the fossilization of abundant vegetation facilitated by a warm and humid equatorial
climate that reigned over Western Europe, some 350 million years ago (an illustrated insert in
Chap. 2 volume I provides a diagram of continental drift since 540 Ma). Fifty million years
later, the sediments of these same regions, red sandstone, poor in fossils and associated with
evaporites testify to the replacement of forests by desert areas, dotted with occasional highly
saline lakes, similar to what we currently find in Saharan Africa. Humidity gave way to intense
aridity and we had no idea why. It was not until the discovery of plate tectonics that we
realized that Europe had slowly drifted toward the tropics. This transformation of the face
of the Earth due to tectonics is illustrated through 16 maps in Chap. 2 volume I.
The discovery of glaciations was a revelation for the geologists of the nineteenth century.
A major polemic broke out at the Swiss Society of Natural Sciences in Neuchâtel when, in
1837, its president Louis Agassiz presented his explanation, incredible at the time, for the
presence of gigantic boulders that dot the Jura mountains. He daringly claimed that these
erratic boulders were not the remnants of the Biblical Flood, but rather enormous rocks
transported over long distances by gigantic glaciers which used to cover the high latitudes of
our hemisphere.
The controversy died down quickly, when European and American geologists discovered
traces of glaciers all over the Northern Hemisphere, just as Agassiz imagined. In Europe, as in
North America, mapping of the terminal moraines left behind by glaciers when they melted
showed proof of the presence of gigantic ice caps in a past that seemed distant. especially since
there was no idea how to date them.
As the idea of the Biblical Flood fell out of favor, a new theory, based on astronomical
phenomena, soon appeared. Scientists like Joseph Adhémar and James Croll realized that there
were small, quasi-periodic variations over time in the movement of the Earth around the Sun
and suggested that associated mechanisms could periodically cause glacial advances and
retreats. Finally, it was Milutin Milankovitch, a professor in Belgrade, who would lay the
foundations for a complete mathematical theory of glaciations, the legitimacy of which was
proven when paleoceanographers found the frequencies of orbital parameters reflected in the
isotopic analysis of marine cores. We now know that the last one of these glacial periods
culminated only 20,000 years ago and was preceded by many others.
The great contribution by Milankovitch was to plant a new idea within the scientific
community: Ancient climates are not only of immense curiosity to geologists; they obey the
same physical laws as those governing the current climate.
This intellectual revolution has had far-reaching consequences and has profoundly altered
the approach to the study of ancient climates making paleoclimatology a science with many
links to geology, geochemistry, oceanography, glaciology as well as the approach to the
physical and dynamic dimensions of the climate. The first part of this book describes the
ix