HOW THE EARTH FELL APART
"Speak to the Earth, and it shall teach thee."
-- Old Testament: Job, xii, 8.
What Shall We Call the Bits?
As we develop the theme of this book further, we will be
dealing with portions of the Earth's surface of every size, from small islands
like Rottnest, right up through the parts and wholes of present continents and
on to the complete cap of continental material which once covered the whole of
the smaller Earth.
The only name commonly in use for any of these areas is the word 'plate'. We
will see shortly that this is not a particularly appropriate word. If a large
plate is broken into a hundred pieces, is each of these a plate?
In this book, I will will using the general word 'domain' for
areas of any size which have taken part in the Earth surface shifts described.
This is on analogy with magnetic domains, the different magnetized areas of a
magnetic material. These may be of any size, and if a large domain is split
into a number of smaller parts, each of these is validly called a domain.
For larger domains, comparable in size to continents or the conventional
tectonic plates, the form 'megadomain' will be used. However, a megadomain
means something rather different to either a continent or a tectonic plate. The
word 'continent ' means a large, contiguous area of the Earth's surface which
is above sea-level. We will see that none of the present continents is a simple
megadomain, instead all are aggregations of one or more megadomains with a
number of smaller parts.
In my view, so-called tectonic plates are just the areas within strings of
different domain boundary segments which are currently in active movement.
Different boundaries of the same domain will usually be undergoing different
degrees of movement, at any one time the majority of them will be relatively
stationary.
Thus a tectonic plate is not a real entity in any permanent sense. Its extent
is only defined from the strings of active domain boundaries, and in reality
some of these will be so inactive as to be included only to make up a complete
figure. Hence the boundaries of 'plates' are only arbitrary, and their
subjective nature naturally leads to arguments as to where particular plates
extend to, or whether they are really several smaller plates.
Proposition 5A
A tectonic plate is not a real entity in any permanent sense, but only
the area within an arbitrary assembly of more or less active parts of domain
boundaries
Aggregates of smaller domains have been identified
in various parts of the Earth, and to these the word 'terrane' has been
applied. These will figure later on in the book. While I believe that 'terrane'
is a valid concept and word, for consistency the term 'microdomain' will be
used in this book.
For the complete cap of continental material covering the whole surface of the
smaller Earth, the term 'holodomain' will be used.
The First Megadomains
We have seen from Chapter 4 that it is reasonably clear
which of the major present land areas were part of the southern megadomain,
Gondwanaland, and which belonged to its northern counterpart, Laurasia.
Now we can go into the nitty-gritty of how, and why, it occurred. But first we
need to look at some figures on land areas, which lead to a conclusion initially
surprising, but obvious in retrospect.
It is accepted that Laurasia included most of Europe, North America, and Asia,
and that Gondwanaland included most of Africa, South America, Australasia, and
Antarctica. The land areas of these continents (in million square kilometres)
is as follows:
|
First Approximation |
|||
|
Laurasia |
Gondwanaland |
||
|
Europe |
9.9 |
Africa |
30.3 |
|
North America |
24.4 |
South America |
17.8 |
|
Asia |
44.8 |
Australasia |
8.5 |
|
|
|
Antarctica |
14.0 |
|
TOTAL |
79.1 |
TOTAL |
70.6 |
We can see that the two megadomains were of roughly similar size, even on this crude first approximation. Refining these figures one stage more,
we know that there is very strong evidence that India and Southeast Asia were
part of Gondwanaland rather than Laurasia. These two regions have a total area
of about 7.7 m sq km. Subtracting this from Laurasia and adding it to
Gondwanaland, we get:
|
Second Approximation |
|||
|
Laurasia |
Gondwanaland |
||
|
As above |
79.1 |
As above |
70.6 |
|
less India/SE Asia |
7.7 |
plus India/SE Asia |
7.7 |
|
TOTAL |
71.4 |
TOTAL |
78.3 |
On the second approximation, the two totals are a bit closer, but not
satisfyingly so. Now is the time to bring in a point of detail of great
importance.
Antarctica, the Fake Continent
We need to look more closely at the figure for Antarctica;
it conceals a basic error which appears to have been ignored, in spite of
readily available evidence. Antarctica is a fake continent. Much of its assumed
land area is, in fact, sea -- or rather would be if the ice was melted. The
South Pole itself lies some 1000 metres below sea level.
This is not in any sense new information. It appeared, for example, in the 4th
edition of the National Geographic Atlas in 1975, from which Fig. 5.1 is
derived.
Figure 5.1 shows the conventional outline of Antarctica, and within it, the
areas which are probably 'real' land, in the sense that they would be above sea
level if the covering ice was removed and the sea allowed to flow in. In fact,
only the part of Antarctica below Australia appears to contain a real landmass,
the part below South America is actually only a chain of small islands. We
still don't have the full picture, but as an approximation it appears that the
real land area of Antarctica is only about half the 14 million square
kilometres usually quoted.
Proposition 5B
Antarctica is not a real continent, but an assembly of islands, with a
land area probably totalling no more than half the 14 million square kilometres
usually assumed
This point seems to have been completely ignored in
previous reconstructions of how the continents fitted together in earlier
times, whether on the old continental drift basis or using the newer expanding
Earth approach. Nearly all these reconstructions have a great lumpy Antarctica
stuck between Africa and Australia, and of course this strongly affects the
matching.
Laurasia and Gondwanaland were Equal!
When we adjust the Laurasia/Gondwanaland figures for this
new smaller value for Antarctica, we get:
|
Third Approximation |
|||
|
Laurasia |
Gondwanaland |
||
|
As above |
71.4 |
As above |
78.3 |
|
|
|
less Half Antarctica |
7.0 |
|
TOTAL |
71.4 |
TOTAL |
71.3 |
and this agreement is excellent. Its relevance will be becoming apparent.
Of course, it is possible to go on into a Fourth Approximation. The areas of
Central America, the Caribbean, California, Florida, Spain, Arabia, Atlas
Mountains, Southern China, and Japan all contain a mixture of plant elements
which make their positioning in either Laurasia or Gondwanaland a little less
than certain. The exact land area of Antarctica is yet to be determined.
Greenland is also partly a fake, as it is hollow, and the same may apply to
other Arctic islands. But the general picture is clear --- Laurasia and
Gondwanaland were close to having identical land areas.
Proposition 5C
The former megadomains of Laurasia and Gondwanaland had the same surface
areas
On now to the actual course of events. Assuming
that there was once a solid 'skin' of continental matter covering the whole
surface of the Earth, and this Earth then expanded under the skin so it split
into pieces, how might we expect this to proceed?
Formation of the Equatorial Girdle
Well, the first thing which might happen is that the skin
would split in half along the equator, into two equal 'caps', leaving a
depressed 'oceanic girdle' around the Earth. This would be reasonable, both
from the point of view of symmetry (where else would the line of weakness be?)
and from a factor relating to conservation of momentum which we will look at
later. And as further supporting evidence, we have the marked equality of area
of Laurasia and Gondwanaland.
Proposition 5D
The first major event in Earth expansion was the splitting of the
holodomain in half, along the Equator, to form the two megadomains of Laurasia
and Gondwanaland
There is considerable evidence for the past
existence of such an 'oceanic girdle' , which has sometimes been called the
Tethys or Tethyan Sea. In fact its existence has been a stumbling block to some
of the earlier, pre-expansion theories of the development of the Earth. In
Chapter 13 (on fossil fuels) we shall also see an important implication of this
equatorial marine girdle, which will be referred to here as the Tethyan Girdle.
What Happened Before the Split?
In postulating the Equatorial Split as the first major
event of Earth Expansion, it is reasonable to ask what happened before it, to
make it happen when it did. Why did the Earth suddenly undergo this paroxysm of
expansion?
I believe that there was no sudden event, the Equatorial Split was just a very
obvious effect of processes which had been taking place for a long time
previously. In this connection, we should look first at changes in the
rate at which expansion has occurred in the past.
Carey has suggested [Carey, 1987] that the rate of Earth Expansion has been
accelerating continuously during the measurable past. In earlier eras, the rate
of expansion was slower, and the further you go back, the less the rate of
expansion. It appears possible, in fact, that expansion has always been
occurring during the Earth's physical evolution, but that the effects have only
become really obvious as the rate has speeded up, especially in the last
200-400my .
It appears that the distinguishing feature of the Equatorial Split was that
this was the first occasion during which the skin of continental material
covering the Earth was stretched thin enough to split open and expose the
'oceanic' rock material underneath. According to this scenario, movements of
the material covering the Earth's surface had occurred previously, but these
had only served to thin out the layer of lighter continental material, and not actually
breach it.
Proposition 5E
The Equatorial Split which created the two megadomains of Laurasia and
Gondwanaland was notable for the first surface exposure of underlying 'oceanic'
material, as the overlying continental material was thinned out by past
expansion
We will pass on now to look at what happened
subsequent to formation of the Equatorial Split, when Laurasia and Gondwanaland
were themselves beginning to split into smaller parts. And here we can gather
further evidence through looking at what happened to domains of different
sizes; their size does seem to have had an effect on their subsequent
behaviour.
Flight of the Microdomains
As an example, look at Fig.
5.2, a map of areas of occurrence of fossil and modern hickories, taken from
'Tree Ancestors', a most interesting book by Edward Berry [1923]. This can be
compared with Fig.4.11 in the previous chapter, showing the current
distribution of Carya, the pecan and hickories.
Notice that in addition to the modern areas, fossil remains of hickories have been
found in Greenland, Iceland, Alaska, and even in tiny Svalbard (Spitzbergen),
only a few degrees below the North Pole.
This leads to a most important point. The usual interpretation of Fig. 5.2 is
that the climate in southern Greenland, Iceland, and the other fossil locations
must once have been warm enough for hickories to grow there. While this may be
true, the implied assumption that warmer climates once extended to much more
northerly latitudes is not necessarily so. In reality, microdomains carrying
these fossils may have individually moved north, out of warmer zones, after the
fossils were deposited.
Proposition 5F
Fossils of warmer-climate plants found in areas with colder climates may
have been carried there by domain movement
If this proposition is true, it does of course
throw confusion and doubt into the whole area of studies of climate in past
eras (paleoclimatology). The same is true of other aspects of geology and Earth
sciences which assume current parts of the planet were always in the same
positions as now.
Proposition 5G
All areas of the Earth sciences which implicitly assume a fixed Earth
must be subject to detailed reconsideration in the light of possible domain
movements
Next extract: The Origin of Volcanoes
Return to Nuteeriat Mainpage