The maturing of the Earth sciences has led to a
fragmentation into subdisciplines which speak imperfectly
to one another. Some of these subdisciplines are field
geology, petrology, mineralogy, geochemistry, geodesy and
seismology, and these in turn are split into even finer units.
The science has also expanded to include the planets and
even the cosmos. The practitioners in each of these fields
tend to view the Earth in a completely different way.
Discoveries in one field diffuse only slowly into the
consciousness of a specialist in another. In spite of the fact that there
is only one Earth, there are probably more Theories of the
Earth than there are of astronomy, particle physics or cell
biology where there are uncountable samples of each
object. Even where there is cross-talk among disciplines, it is
usually as noisy as static. Too often, one discipline's un~
proven assumptions or dogmas are treated as firm boundary
conditions for a theoretician in a slightly overlapping area.
The data of each subdiscipline are usually consistent with a
range of hypotheses. The possibilities can be narrowed
considerably as more and more diverse data are brought to bear
on a particular problem. The questions of origin,
composition and evolution of the Earth require input from
astronomy, cosmochemistry, meteoritics, planetology, geology,
petrology, mineralogy, crystallography, materials science
and seismology, at a minimum. To a student of the Earth,
these are artificial divisions, however necessary they are to
make progress on a given front.