Geoscience Reference
In-Depth Information
age of the Earth, which he considered to be over 2 billion years old. He
also suggested that man had been in existence for four hundred thou-
sand years. No wonder nobody would publish this work for many
years! These conclusions were fantastic, and well beyond the compre-
hension of eighteenth-century readers and scientists.
It is now well documented that changes in sea levels have
occurred in the geological past. These eustatic changes, as modern-
day geologists term them, do not just occur in one direction. Sea levels
have fluctuated markedly in the past: recent changes associated with
the last Pleistocene ice age resulted in Ireland and Great Britain being
joined to continental Europe for a period as sea levels fell, before rising
sea levels separated them again, both from it and from each other.
Maillet did not recognise that levels could fluctuate, nor did he realise
that continental masses could, by various methods, be elevated out of
the sea so that marine sediments could easily be found as a result at
high altitudes. This is hardly surprising as these ideas were only
formulated as late as the 1920s.
Certainly these early empirical age estimates of Lhwyd, Halley and
Maillet for the Earth were wrong; but they were the first serious
scientific attempts at precise geochronology and should be respected
as such. Later, in the nineteenth century, other methods using sedi-
mentation rates and revisitation of the salt-method followed, before
the breakthrough in the twentieth century of radiometric dating.
