In these chapters I have shown that our Earth has doubled its diameter in the past
320 million years. I am not the first person to have suggested that the Earth was
getting larger, scores of science-minded people, over the last 150 years, have also
concluded that the Earth is growing in size.
I have suggested a mechanism on how planets grow in size. This is essentially a growth
process by the diffusion of ions (adding mass) and not an expansion process with
constant mass. The growth is ‘internal’ - below the crust (in rocky planets) or in
the lower atmosphere of gaseous planets. We know that when mass is added to a rotating
body it slows it down. Our planet’s rotation period is slowing down and as a consequence
each day is getting longer by an infinitesimally small amount. Since the 1950’s,
with the advent of the atomic clock, we have been able to measure time very accurately
and around 0.7 of a second should be added to the length of each year to correct
The profile of the Earth’s crust varies considerably and this is because it has been
subject to strain caused by this internal growth mechanism. What was originally
a thick and uniform crust on an small planet, billions of years ago, has been ‘stretched’
to successively thinner profiles and even to failure in some areas. The first failure
of the old crust appears to have happened at a suture between east Asia and Antarctica,
some 300 million years ago.
So the Earth, in the Carboniferous Period, was likely the size of Mars and occupied
the same orbital position. It appears that Mars has also undergone considerable strain
on its crust, its northern hemisphere now having a much thinner crust than its southern
one. This stretching of the crust will have smoothed out many of the craters which
will have existed previously in the northern hemisphere. Cratering on Mars is largely
confined to the southern hemisphere where the crust has suffered less stretching.
Crustal rock can behave in a plastic way if subjected to protracted strain - as the
constituent silica and alumina chains re-align themselves and slip over each other
in the process of creep. This can be likened to a toffee bar being stretched apart.
Hydrostatic pressures acting on the underside of the crust searches out its weakened
areas and repeatedly works on them - causing successively more deformation. This
strain deformation accounts for much of the metamorphism of igneous materials.
The fragments of Cambrian meta-sedimentary slabs which exist in many parts of the
World were likely assembled on a much smaller Earth (30% present diameter) where
they formed a contiguous covering. The distribution and abundance of these slabs
is consistent with this hypothesis. Many fragments have been separated from each
other in a symmetrical fashion as the basement crustal material between them has
stretched apart. An example of this is the symmetry of Tanzanian sedimentary structures
with those of the Western Ghats of India.
In the early days of a young planet Earth, the hydrostatic pressures building up
below a thick crust will have been relieved, most often, by extremely violent volcanic
activity. The eruptions will have caused the formation of many craters and ash clouds
- and the latter would settle as layered deposits. Our Earth was covered with water
at the time and so these deposits will have formed sedimentary structures in an aqueous
environment. Mars, on the other hand, lacks water and its ash deposits have formed
‘sedimentary’ structures in a dry environment. However, they too have fragmented
and separated from each other in a similar way they have done here on Earth.
A very young Earth will have possibly looked like the planetesimal Ceres which resides
in the orbital position between Mars and Jupiter. It is considered that Ceres also
has a thick crustal structure. This may have formed when the rocky planet was at
the centre of a gaseous planet similar to Jupiter. The overburdening weight of a
massive envelope of hydrogen and helium would have meant extreme compressive forces
acting on it.
I highlight the possible existence of a ‘gravity gradient’ which acts radially in
the Solar System. This gradient has several components but primarily describes the
distribution of the element hydrogen at varying energy levels. Elements at the lighter
end of the Periodic Table tend to be more abundant in the outer reaches of the solar
system - their penetration apparently held back by pressure of the solar wind. This
means that at successive stages of planetary growth, the suites of diffusing ions
gradually become heavier as the planet migrates closer to the Sun.