304 Epilog
tion processes responsible for sea-floor spreading and continental drift. Ridge-crest
processes took center stage as it became clear that the interaction between seawater
and basalt is a determinant factor in ocean chemistry. Deep-sea biology made headlines with the discovery of an entirely new kind of deep-sea community, the hot vent
assemblage on the East Pacific Rise. These communities represent a food web whose
base is chemosynthesis: the oxidation of sulfide issuing from the vents by archaic
bacteria specially adapted to high pressure and high temperature. The fact that sunlight is unnecessary to sustain primitive life forms has led to new speculations about
the conditions surrounding the origin of life. Was Earth's heat the energy source
nourishing the first living things?
Also in the 1970s, stratigraphy and its offspring paleoceanography received a
tremendous boost from deep-sea drilling. The main features of the Cretaceous and
Cenozoic history of the ocean were established, using biostratigraphy, magnetostratigraphy, and chemostratigraphy (mainly the isotopic ratios in the elements oxygen,
carbon, and strontium, as recorded in calcareous microfossils, and also the preservational state of the fossils, which records saturation and reactivity of deep waters). It
was found that the great evolutionalY breaks near the epoch boundaries were not an
artifact of poor preservation of the record, which is so common in the land sections.
Deep-sea sediments are made mainly of fossils, so neither was there any question of
missing the message due to lack of messengers. What emerged is that in the ocean
evolution proceeds mainly in distinct steps rather than gradually, and that major
discontinuities are tied to rapid climatic change.
Drilling in the margins discovered their architecture and established the course
and effects of continental break-up (in the Atlantic) and of continental accretion (in
the Pacific). Seismic stratigraphy, in conjunction with drilling results, greatly expanded our knowledge about margin structure and margin processes, and allowed the
(tentative) reconstruction of sea level variation on a global scale.
In the meantime, Quaternary research on the youngest deep-sea sediments established the cyclic nature of the record, and the dominance of astronomic forcing within
the background climatic fluctuations which characterize the "normal" situation between the climate steps.
The discoveries of the 1970s provided the base for the search for mechanisms in
the 1980s. The new catch phrases are "earth dynamics" and "global systems" and
they will continue to be most important. How does mantle convection control tectonic
or geochemical processes at the Earth's surface and how is it tied to the coevolution
of climate and life? How is the chemistry of the ocean and of the atmosphere determined, and what is the role of the circulation of seawater through the ocean crust and
through the ocean margins, and how is this circulation affecting crustal materials?
How do hot vents (on ridge crests) and cold seeps (along the margins) control the
abundance and diversity of chemosynthetic-based communities? How do ocean processes (productivity, sedimentation) codetermine climate? What exactly happened at
those times when extinction (or speciation) greatly accelerated in the ocean?
Significant contributions to these major topics came from all disciplines, but several major discoveries and developments set the tone. For the study of mantle
processes (degree of mixing, nature of layering), three-dimensional seismic tomo-
tion processes responsible for sea-floor spreading and continental drift. Ridge-crest
processes took center stage as it became clear that the interaction between seawater
and basalt is a determinant factor in ocean chemistry. Deep-sea biology made headlines with the discovery of an entirely new kind of deep-sea community, the hot vent
assemblage on the East Pacific Rise. These communities represent a food web whose
base is chemosynthesis: the oxidation of sulfide issuing from the vents by archaic
bacteria specially adapted to high pressure and high temperature. The fact that sunlight is unnecessary to sustain primitive life forms has led to new speculations about
the conditions surrounding the origin of life. Was Earth's heat the energy source
nourishing the first living things?
Also in the 1970s, stratigraphy and its offspring paleoceanography received a
tremendous boost from deep-sea drilling. The main features of the Cretaceous and
Cenozoic history of the ocean were established, using biostratigraphy, magnetostratigraphy, and chemostratigraphy (mainly the isotopic ratios in the elements oxygen,
carbon, and strontium, as recorded in calcareous microfossils, and also the preservational state of the fossils, which records saturation and reactivity of deep waters). It
was found that the great evolutionalY breaks near the epoch boundaries were not an
artifact of poor preservation of the record, which is so common in the land sections.
Deep-sea sediments are made mainly of fossils, so neither was there any question of
missing the message due to lack of messengers. What emerged is that in the ocean
evolution proceeds mainly in distinct steps rather than gradually, and that major
discontinuities are tied to rapid climatic change.
Drilling in the margins discovered their architecture and established the course
and effects of continental break-up (in the Atlantic) and of continental accretion (in
the Pacific). Seismic stratigraphy, in conjunction with drilling results, greatly expanded our knowledge about margin structure and margin processes, and allowed the
(tentative) reconstruction of sea level variation on a global scale.
In the meantime, Quaternary research on the youngest deep-sea sediments established the cyclic nature of the record, and the dominance of astronomic forcing within
the background climatic fluctuations which characterize the "normal" situation between the climate steps.
The discoveries of the 1970s provided the base for the search for mechanisms in
the 1980s. The new catch phrases are "earth dynamics" and "global systems" and
they will continue to be most important. How does mantle convection control tectonic
or geochemical processes at the Earth's surface and how is it tied to the coevolution
of climate and life? How is the chemistry of the ocean and of the atmosphere determined, and what is the role of the circulation of seawater through the ocean crust and
through the ocean margins, and how is this circulation affecting crustal materials?
How do hot vents (on ridge crests) and cold seeps (along the margins) control the
abundance and diversity of chemosynthetic-based communities? How do ocean processes (productivity, sedimentation) codetermine climate? What exactly happened at
those times when extinction (or speciation) greatly accelerated in the ocean?
Significant contributions to these major topics came from all disciplines, but several major discoveries and developments set the tone. For the study of mantle
processes (degree of mixing, nature of layering), three-dimensional seismic tomo-