1. juni 2010

Avslører 70 millioner år gammelt havnivå

Da dinosaurene ble utryddet for 65 til 70 millioner år siden sto havnivået hele 170 meter høyere enn i dag. De verdensomfattende oversvømmelsene i det hete klimaet var dermed mer omfattende enn det forskerne hittil har trodd.

Sea levelThe period towards the end of the cretaceous era was followed by a gradual sinking of the sea bed, making the sea level retract.

An international group of scientists have – with far greater accuracy than before – managed to model the sea level at this period, known by geologists as the cretaceous period.

Scientists from Norway and Australia has investigated past oceans with particular interest in how the sea level is affected by the relations between ocean-floor spreading and the effect of mantle convection.

The result of this extensive research was published in the prestigious scientific magazine Science on March 7.

The team

Gaina_SteinbergerThe scientists Carmen Gaina and Bernhard Steinberger.A substantial team of scientists are responsible for the new estimates:

  • Carmen Gaina is the manager of the geodynamics team at the Geological Survey of Norway (NGU). The Rumanian scientist’s field is plate tectonics where she among other factors combines gravity measuring, soundings data, magnetism and seismology to reconstruct different regions across the globe.
  • Bernard Steinberger works at the geodynamics team at NGU. The German geophysicist’s top competence is numeric modelling of mantle convection, the movements of hotspots and changes in the Earth’s axis of rotation.

With their colleagues R. Dietmar Müller and Maria Sdrolias at the University of Sydney and Christian Heine at Statoil Hydro they have advanced the knowledge of the Earth in the cretaceous period.

Earth in the cretaceous era

“Our compilation of sea level curves at the end of the cretaceous era has provided us with an improved frame of reference for further research, but also as a tool of exploration for natural resources and modelling of long-term climatic changes,” said Bernhard Steinberger.

The cretaceous era is one of great importance to geology. In the period from 145 to 65 million years ago, the Earth was marked by several great floodings. The climate was very hot and there were no continuous layers of ice. Porous rock was formed to which today’s North Sea oil found it’s way and storage.

On dry land, the dinosaurs dominated at the same time as flowering plants that are closely related to birch, oak and poplar evolved massively. Flagellates and foraminifers – one-celled animals used by today’s climate researchers to investigate past climatic changes – swam in the oceans.

Uncertain calculations

The period towards the end of the cretaceous era was followed by a gradual sinking of the sea bed, making the sea level retract. Scientists have long disagreed on the actual sea level of this period. The calculations have varied between 131 and 820 feet higher than today’s level.

“Our modelling shows a sea level at 558 feet higher than that of today’s,” said Bernhard Steinberger.

“The results support the theory regarding the mantle convection affecting the topography and playing an important role in subsidence of the continental margins,” he added.