Sea level 'to fall over long-term'

Ancient sea level superimposed on today's continents

This is what the modern world might look like if it had to contend with the sort of sea levels that existed 80 million years ago, at the time of the dinosaurs.

The dark blue areas show regions of land on today's continents that would be under water.

Back in the Cretaceous Period, when the climate was very hot, the Earth's ice sheets had melted and sea levels were 120m above what they are today.

In new research, Dr Dietmar Muller of the University of Sydney, Australia, and colleagues have reconstructed the vanished ocean basins of that time, and have used their model to assess how they will evolve in the future.

The team looked at data on ocean crust production, ocean sediment build-up and tectonic plate boundaries.

The researchers were able to demonstrate that over the long-term, sea level will fall - despite the current rises being experienced due to global warming.

This is being driven by geological processes that are working to deepen the basins.

The model is described as the first to comprehensively map the planet's oceans from the Cretaceous Period, when Gondwana - the supercontinent that later broke up into Australia, Antarctica, South America and Africa - was intact. The Indian and Atlantic oceans were formed in this period.

"To give an idea of the time-scale that our ocean basin model covers, it starts at the time when dinosaurs were at their most diverse, mammals were small and a minor component of animal life on Earth, and flowering plants were just spreading over the Earth," says Dr Muller.

"If we project our model 80 million years into the future, we can predict that the sea level will continue falling by about 120m in the long run, through mid-ocean ridge destruction and the continuing ageing and deepening of the ocean basins," he explains.

The study is published in the journal Science.