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CHAPTER 1.2
THE STANDARD
THEORY
The purpose of this book is to introduce Ben's Antipodal
Impact Theory as the best explanation for the major mass extinctions. However,
the best place to begin is to start with an explanation of the Standard Theory
of geological formation, regarding the effect of cosmic impacts, continent
formation, tectonic plate movement, deep water trenches, subduction, hotspots
and island arcs.
While there is no absolute Standard Theory of
Geological Formation, there are generally accepted ideas. In this chapter, I
will present those generally accepted ideas. 3,4
The Standard
Theory views the Earth as having a hard outer crust, varying from a minimum
thickness of four miles in deep parts of the ocean where it is denser, to as
much as 40 miles in thickness on the continents. The crust is composed of two
different types of silicates. The continental tectonic plates are composed of
lighter, Felsic rocks, such as granite. The ocean floor is composed of somewhat
heavier Mafic material, mostly basalt and gabbro. This outer crust, along with
the lithospheric mantle (the hard, brittle part of the mantle), is called the
lithosphere.
Below the crust are three other layers (these layers can
be subdivided into even finer divisions, theoretically). The three other layers
(starting closest to the lithosphere) are:
1. The Mantle—1800
miles thick, composed of four different layers.
a. Upper Lithospheric Mantle -- Separated from
the crust by the Mohorovic discontinuity, the Lithospheric Upper Mantle
consists of ultramafic rocks that, like the crust, are hard and brittle.
b. Asthenospheric Upper Mantle -- Solid, but
ductile ultramafic material.
c. Transitional Mantle -- Ultramafic material.
d. Lower Mantle -- The rock is hot enough to
flow ... ultramafic material.
2. The Outer Core—1400
miles thick, composed of molten nickel and iron (relatively heavy).
3.
The Inner Core—770 mile radius, composed mostly of solid nickel and iron
(even heavier). 109
CONTINENT FORMATION
Relatively little is written about continental formation or continental uplift
except to say that:
"During its violent, molten infancy, earth began
to settle into layers: The densest elements sank and formed the core, the
lightest migrated upward to form the crust, and all the rest ended up in the
mantle…" 5
We are left to draw the
conclusion that the shapes of the continents are random and that their heights
(mountains and high plateaus) are the results of tectonic plate collisions or
volcanic uplift (mantle plumes caused by convection currents?).
The
felsic material of the continental plates is lighter than the mafic material of
the oceanic crust, and therefore, floats higher than the oceanic crust.
THE EFFECT OF COSMIC IMPACTS
The Standard Theory does not regard the effect of cosmic impacts on
Earth's surface as significant (except at the impact site) as long as the
impact does not penetrate the lithosphere. 6
According to
the Standard Theory, the effect of a non-invasive cosmic impact on the Earth is
much like that of a bug impact on the windshield of a car, while the car is
moving down the highway. Or, at most, the impact would be like a small pebble
that might make a slight nick in the glass.
Now this is not to say that
the impact site, itself, might not see significant effects. However, the
Standard Theory would not expect to see noticeable effects at the antipode of
the impact.
TECTONIC PLATE MOVEMENT
There
are 12 major tectonic plates on the earth's surface, according to the Standard
Theory. The Standard Theory states that many of the earth's geological features
can be explained by the movements of these plates (mountain ranges, island
arcs, trenches). 4 page 4
Much of the movement of these
tectonic plates is caused by sea-floor-spreading at the mid-ocean ridges. The
Standard Theory later amends this description to pronounce that
sea-floor-spreading is actually caused by subduction of oceanic plates at other
locations. The sea-floor-spreading is actually just a passive response to the
loss of sea floor being subducted in other locales. Generally the subduction is
thought to be initiated by convection currents in the mantle.
SUBDUCTION & DEEP WATER TRENCHES
The Standard Theory states that there are three major types of tectonic
plate boundaries. These Boundaries are:
1. Divergent Boundaries—New crust being
created as the plates pull away (e.g. the mid-ocean ridges).
2.
Transform-Fault Boundaries—Two plates sliding past each other.
3.
Convergent Boundaries—Two plates moving into each other. There are three
different types of convergent boundaries. They are:
a. Oceanic-Continental Convergence—The
oceanic plate pushes into and subducts underneath the lighter continental
plate. It also pushes up the continental plate forming mountain ranges and
volcanoes (as the subducted plate and water in it is heated to steam and
rises).
b. Oceanic-Oceanic Convergence—One of the
plates is subducted beneath the other, creating a trench and sub-oceanic
volcanoes, resulting in island arcs.
c. Continental-Continental
Convergence—Two Continental plates smash into each other and neither one
subducts. The rocks are relatively light and resist downward motion. The crust
tends to buckle and be pushed upward or sideways. "The collision of India into
Asia 50 million years ago caused the Eurasian Plate to crumple up and override
the Indian Plate. After the collision, the slow continuous convergence of the
two plates over millions of years pushed up the Himalayas and the Tibetan
Plateau to their present heights. Most of this growth occurred during the past
10 million years." 3
HOTSPOTS
According to the
Standard Theory, a hotspot is a "plume" of lava from deep within the mantle
that spews forth lava and creates islands as an ocean plate passes over it. The
Hawaiian Islands are part of an island arc (mostly composed of hidden sea
mounts) that was created by a hotspot that continues to form more islands.
Loihi, the next Hawaiian island, is now forming beneath the surface of the
ocean.
It is important to note that the Standard Theory views these
hotspots as being fixed in the mantle, with any appearance of movement being
due to the movement of the tectonic plate above that hotspot. In explaining the
hotspot that fuels the creation of the Hawaiian Islands, www.platetectonics.com
writes:
"Geologists believe that a huge column of
upwelling lava, known as a "plume" lies at a fixed position under the Pacific
Plate. As the ocean floor moves over this "hotspot" at about five inches a
year, the upwelling lava creates a steady succession of new volcanoes that
migrate along with the plate — a veritable conveyor belt of volcanic
islands." 3 page 17
The Standard Theory does
not offer a definitive reason for the existence of the plume which causes the
hotspot. Some speculation focuses on the possibility that the plume is part of
a heat release mechanism from the interior. But the Standard Theory does not
offer a definitive explanation.
ISLAND ARCS
Several locations
in the ocean feature arcs of islands. Notable among these island chains are the
Aleutians, the Kuriles, the Ryukyus and the Philippines, as well as the
Indonesian islands and the Solomons.
The Standard Theory sees these
island arcs as being created as result of subduction, when certain magmas from
the subducted oceanic plate are heated up and rise to the surface to become
volcanoes.
These island arcs are regarded as features related to
trenches at subduction zones. As for the elegant arc shape of the islands,
scientists believe that "it has something to do with the curvature of the
earth." 3 page13 |
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