dynamic entity in which the anomalies, the long wavelength cores in particular,
reflect convective processes in the Earth's interior? [Look at the debate amongst
the leading geophysicists in the early 1960's when the first satellite results were
obtained.] Now there would be no doubters that the gravity field provides
constraints on models of dynamic evolution of the Earth but plausible interpreta
tions are possible only if other data types are introduced - information on the
Earth's rheology or stress-bearing capacity of the crust and mantle, seismological
information on lateral variations in seismic velocities and attenuation, surface
heat flow, and tectonic histories of the crust.
A third example is provided by sea-level change. Tide gauges have monitored
sea-level for only about 100 years and then only at few locations. The records
reveal a complex behaviour of the relation between crust and sea-level. In some
areas sea-level is rising, in others it is falling. What are the causes? Is it tectonic;
the subsidence or emergence of a crust acted on by tectonic forces? Is it eustatic;
the change in ocean volume due to, for example, an exchange of mass between
the oceans and ice sheets? Is it anthropogenic; the rise in sea-level produced by
a global warming of our environment? It is undoubtedly a bit of all and one is
hard-pushed to interpret the tide gauge data in a unique way. Again, the record
has to be extended back in time (as well as the present record improved). Here
the older record includes archaeological information, sedimentological and
geomorphological evidence, and a reasonable picture begins to emerge of how
sea-level has changed in time over the past 10,000 or so years.
N
359
Angerman River
Gulf of Bothnia
Zuid Holland
E o
r - r r -•t
a a -
2c
2
1
T Christchurch -
r New Zealand
i iii1iii
time (x 1000 years BP)
Karumba
Queensland,Australia
8 -6 -4 -2
time (x 1000 years BP)
Figure 3
