As the planet has grown in size, the crust of the Earth has increased its surface
area in three ways:
A) by intrusion of new magma into the existing crustal surface.
B) by the stretching and thinning of the crust’s profile.
C) by the building of new crustal areas - as in ocean-bed formation.
In the chapter on Evolution of the Earth’s Crust which describes how the crust has
been stretched thinner, sequentially, it leads us to imagine that the young and small
Earth had a very thick crust - perhaps of the order of 90-100 km thick. This thickness
could have come about through compaction by an overlaying weight of hydrogen and
helium, if the planet was, as I suggested, originally the rocky core of a Jupiter-like
structure. I also described the ‘Gravity Gradient’ which suggests that the younger
planet’s crust will have been composed of lighter elements and the crustal specific
gravity has gradually increased as newer material has been added.
So we can picture the Earth’s continental crust as being a mosaic of crustal additions.
The earliest mosaic pieces of crust are to be found scattered around the World -
in what is now the North-West Territories of Canada, South Africa, Australia and
Below is the tiny Earth, some 3.5 billion years ago, with its thick crust. Subsequent
images describe the initial growth stages by magma intrusion.