What is radiocarbon dating process
Using this method we are gradually building up a picture of how the ice sheets have changed over the last 20,000 years.
We have to be similarly devious to work out how quickly our remaining ice sheets are melting.
The land beneath the thickest ice was pushed down by up to half a kilometre, while the land outside the ice sheets bulged upwards by several hundred metres (Figure1a).
This is why the ocean stays stuck to the Earth – because the Earth is a very large mass.
Since the ocean is a liquid, its surface must track a surface of equal gravity (this is also why water in a glass placed on a table forms a flat surface), and we call this surface the ‘geoid’.
Figure 5: Cartoon showing how the change in the shape of the geoid and the rebound of the solid Earth following the melting of an ice sheet results in non-uniform sea-level change.
Red dashed lines in the lower plot indicate the original land/ocean configuration of the upper plot. The reason that this complicates our measurements of sea-level change is because when an ice sheet melts it alters the distribution of mass on the surface of the Earth, and this alters the shape of the geoid.
The reason for this is that the Earth’s mantle – the 2900 km-thick layer within the Earth which lies beneath the rocky layer that we stand on – behaves like a viscous fluid.