There are some other aspects of
continental uplifting and movement that should be covered. That is the purpose
of this chapter.
The nature of subduction and the
directional movement of new continents pretty much guarantees that, over time,
continents will inevitably end up clumping together. They will subduct the
oceanic plate in front of them until they run into another
However, new cosmic impacts can cause
the creation of new continents that will then inevitably
clump together through subduction.
Eurasia is, in effect, the graveyard of
older, clumped continents, drawn together over the eons.
RECONCILING THE NUMBER OF IMPACTS
AND THE NUMBER OF CONTINENTS
The Earth is 4.6 billion years old. If
a continent-producing impact were to hit every 50
million years (approximately the present rate), then why wouldn't we have 90 continents on the surface of the Earth today?
First of all, the rate of impacts was
much higher in the early years of the Earth's history. The hot surface of the
Earth was made and remade again and again and again by large scale impacts. One
impact was so huge that it created the moon.39
After 3.8 billion years ago, the period
of extreme impacts was over and things settled down. Somewhat. There were still
lots of impacts. Gradually, the impacts began to taper off, to a level
approaching modern day.
There are two things to consider about
the early Earth's surface, which was thinner because the Earth was hotter.
1. SMALLER CONTINENTS
Because the Earth's surface was thinner, it meant that there was not so much
shear friction to overcome when uplifting a continent. Therefore, smaller
impacts could cause the uplift of a continent. Also, smaller continents were
possible, creating the small, old "cratons" that are found embedded in some of
2. LOWER UPLIFT Because
the energy needed to uplift an area of crust was lower, the amount of uplift
distance needed to create pressure relief was lower. Continents were not
uplifted as high. Some of the early continents may not have been uplifted as
high as sea level.
The natural process of subduction,
begun by the directional pressure on the lithosphere of a newly created
continent, would eventually cause all of the continents to coalesce. And then a
new large impact would create a big, new, directed continent, which would
eventually clump due to subduction.
When we look for all these older
continents that should be there, we will find that many of them have been
absorbed by the bigger continents and squashed together through the process of
subduction. I believe that there is a reason that so much of the central Asian
land is so high
compressed continents from the early Earth are part of
As the Earth cooled, the lithosphere
became permanently solider and deeper. A thicker lithosphere made it more
difficult for an impact to uplift a continent, and as a result, the uplifting
became rarer and, when it happened, the uplifting was higher.
With the thicker present day
lithosphere, the continent of Western Antarctica is about as small as can be
created at the antipode of an impact.
What we have seen since the end of the
great bombardment, ending about 3.8 billion years ago, is:
1. EARLY YEARS Still
significant impacts creating many sizes of shallow continents. These continents
were eventually squashed together through the subduction process (caused by
directed pressure on surface tectonic plates by newly created continents).
2. LATER YEARS A lower
level of impacts and only occasional continental uplift, averaging about one
every fifty million years. But when it happened,
it was a good-sized continent (compared to the size of the small cratons of the
early days) and the uplift height was significantly higher.
During the past 250 million years, we
have seen the creation of the Siberian Continent, the Western Antarctica
Continent , the Eastern North American Continent, The
South American Continent and the Indian Continent. Two of these (India
and Siberia) ended up in the graveyard of old continents (Eurasia).
Another ended up attached to Eastern Antarctica.
The other two are free floating but headed towards
The other continents that would still
need to be matched up with impacts are:
3. Different areas of Eurasia
Taking into consideration the natural
process of continental coalescing and the number of continents that have not
yet been identified with an impact, there seems to be enough unexplained
continental material to match up with as yet
unidentified (but statistically certain) impacts from the past.
CONTINENTS & TECTONIC
Some people have become understandably
confused about the difference between a continent and a tectonic plate.
Sometimes they seem to be the same thing.
The Standard Theory isn't terribly
useful here. It just lists as continents the seven standard land masses that we
are taught in school and then shows a map of 12 primary tectonic plates, some
of which relate to a single continent and some of which don't. The Standard
Theory doesn't explain the relationship of continents and tectonic plates
it is what it is.
The Theory of Antipodal Impact Effects
looks at the history of the continents and tectonic plates and tries to make
sense of the way that they move and change.
When a continent is first uplifted, it
rides on its own tectonic plate. The uplift frees it from most connection to
other tectonic plates.
However, during the life of a
continent, it can see many changes relating to its condition as a solo player
on its own tectonic plate. South America and Africa are continents that survive
today on their own tectonic plates.
However, some continents smash together
(usually the ocean between them is subducted) and become a combined continent
on a single tectonic plate. Examples of this include North America (which is a
mixture of at least two continental masses) and Antarctica (Western Antarctica
and Eastern Antarctica). Each of these pairs of combined continents share a
The mega-combined continent of Eurasia
has several continental masses (Siberia, India and many other continents that
have captured and absorbed over the ages). Eurasia shares three major tectonic
plates (the Eurasian plate, the Indian plate and a little bit of the North
American plate which controls the eastern tail of Siberia, starting at the rift
at lake Baikal).
The poor old Australian continent has
been broken up into three different plates. There is the top half of the old
Australian blob that is now in the Antarctica plate (as Eastern Antarctica),
the bottom half of the old Australian blob in the Australian plate and the
shattered remains of the Australian tail in the Philippines plate. One should
also note that some of Australia's tail was stolen by the Indian continent
during its uplifting and is now in the Indian plate.
Therefore, continents and plates start
out as one and the same thing. However, as time goes by, that can change.
CONTINENTS, SUBCONTINENTS AND
Another tricky concept is the
difference between continents, subcontinents and cratons.
In this book, I recognize all land
masses that were uplifted as a result of antipodal impact effects as
continents. Therefore, I recognize Western Antarctica and India as continents
They are small continents, but they are still continents, not hotspot islands.
The Standard Theory doesn't have a
clear continental creation mechanism, and therefore, it does not have a clear
definition of what a continent is or is not. Therefore, in accordance with the
vague Standard Theory, many geologists refer to India as a subcontinent. They
refer to Western Antarctica as just part of the Antarctica continent.
When I refer to India, I call it a
continent, unless I am describing it specifically within the structure of the
Standard Theory, when I refer to it as a subcontinent.
Cratons can be old uplifted sections of
rock from, literally, eons ago. Many of these cratons are in excess of three
billion years old. Many were uplifted when the lithosphere was thinner and
continental uplift could occur from smaller impacts. Not surprisingly,
continental uplift from smaller impacts often produced smaller "continents".
Some of the cratons are no bigger than a good-sized island. But some of the
cratons could be really big.
The common denominator involved with
uplifted cratons is the concept that they are really old and the idea that many
have been pulled back into the mantle as the subduction machine pulls new ocean
floor from the mid-ocean ridge and subducts old cratons that don't get snared
by the continent under which the old ocean floor is subducting.
This also means that probably all
remaining old, uplifted cratons are now on land. Many of these remaining old
cratons were part of an ocean floor that was uplifted as part of a new
continent many years ago.
However, there are still some more
recent flow basalt cratons out under the sea, such as the Kerguelen Plateau in
the southern Indian Ocean. 40
A craton can also be used as a term
describing a very large old area of stable rock at a continent's core (a core
that is, in reality, a combination of smaller cratons). I am using the word
craton in its smaller sense. South America and Africa are good examples of
continents that are studded with old cratons. This studded structure is
probably what the sea floor looked like when those continents were uplifted.