Layer Age Estimation
1. In addition to various bits of
information, there are 3 primary principles
geologists use to place layers of
rock according to age. The first, Principle of
Superposition is the
un-changed consecution of the rock, which contains the
oldest stratum (a
single sedimentary rock) located in the bottom of the rock.
Superposition
is the primary method to unveil the order of succession in which
layers were
formed in the rock. The second, Principle of Original Horizontally
states
that most strata is originally formed horizontally, which explains
that
steeply dipping strata was deformed at a much later date. This brings us
to the
third and last, Principle of Original Lateral Continuity. This is a
stratum that
patterned in all directions until the rock layers stopped at the
ends of its
original placement. 2. Catastrophism is a scientific method to
explain extreme
changes in geological structures in a short period of time.
These catastrophism
events may include earthquakes, severe flooding,
volcanoes and extreme wind
conditions. Uniformitarianism is the belief in
slow evolution and slow change in
geological Earth events. This states that
Earth can only change over a long
period of time. Different parties, one
believing in catastrophism and the other
believing in uniformitarianism
collided in the 19th century though being in
close agreement at the same
time. Under closer studies of the Paleozoic and
Mesozoic era, these two
theories posed problems for them, too short for
uniformitarianism and too
long for catastrophism. 3. By using the radioisoyope
dating method,
scientists are able to measure the age of a substance. This
method is
possible for measuring the "invisible radiation emitted by
phosphorescent
substances." These atoms are called parents, and as it
decays it will become
a daughter. By knowing the time it takes for an isotope to
change from a
parent to a daughter, we can measure the time without the
interference of
effects caused by catastrophism and uniformitarianism. To
quickly explain the
measuring process, you must take the # of parents and
daughters mean in the
rock and the percentage of parents remaining should be
added to the measuring
curve scale to find the amount of half-lives remaining.
This will give
you the age of the rock. 4. The planet Earth is estimated 4.6
billion years
old. Scientists were able to reach that number by using
radioisotope dating.
Using this method, scientists have measured from the
Precambrian,
Mesozoic all the way to the present. The process and details of
radioisotope
dating are explained above in 3. 5. a. Precambrian era, being the
longest era
consumed 4 billion of the 4.6 billion years of the Earth's history.
Rocks
during that age contained very little fossil history and were altered so
much
that it makes it difficult to know the conditions of that era. b.
Paleozoic
era began 570 m.y. ago and contained some of the earliest found
life forms
including the Trilobites, sharks, corals and the first life on
continents
including forests, insects and reptiles. The formation of the
northern and
southern Appalachians was also accomplished. c. Mesozoic era
extended from 245
m.y. to 65 m.y.. This era was the death of the long
survived trilobites but the
beginning for dinosaurs and birds and the Andes.
d. Cenozoic era extended from
65 m.y. to the present day. This was the
era of animals including horses, apes,
humans and the formation of the Rocky
Mountains, Alps and Himalayas. Unit II 6.
The Earth's rocks are divided
into 3 different types. The first are igneous
rocks, which are formed by
volcanic magma coming to the surface and cooling. The
second, sedimentary
rocks are formed from the disposition or accumulation of
sediments (mud,
clay, sand, gravel and skeletal remains of plants and animals)
from water,
wind or ice. There also is a second class of sedimentary rock that
is formed
a completely different way. Instead of mechanically depositing, it
is
chemically deposited forming limestones and evaporates. The third and
last
class, is the metamorphic rock. Metamorphic rocks are any rock that has
been
altered by being crushed, squeezed or heated. These rocks can be
identified by
their unique mineralogy and structure. As a result of the
changes, new types of
rocks are formed. 7. Beginning with the granite, the
most well known class of
rock. These rocks have a speckled appearance with
the light gray being its
dominant color. Its chemical composition consists of
high silica and low iron
with magnesium content. Unlike granites, the
andesites are fine-grained and made
up of an intermediate silica volcanic
rock. This brings us to basalt, which are
very dark colored rocks. Only
looking at it very closely reveals the tiny grains
of dark minerals the
construct it. Unit III 8. Published in 1915, Alfred Wegener
introduced
"Continental Drift Theory" to the scientific world. This
theory states the
continents of the planet have moved and are still moving, and
that the world
once possessed only one huge continent (Pangea). Fellow
scientists thought
his idea was nuts, but at the same time it explained some
unanswered
questions involving the discovery of identical organisms found on
separate
continents separated by thousands of miles of ocean. 9.
Comparing
Wegener's theory to the current theory of plate tectonics
brings us to believe
that he was not exactly correct but was on the right
path. The Earth's plates
will overlap or push other plates giving them the
ability to move very long
distances. The new theory says that the plates
moved and not just the
continents. The plates may include the continents, the
ocean floor or both. This
concludes that continents can not move if the ocean
floor doesn't, they must
move together. 10. Plate boundaries are broken up
into 3 different groups:
rifts, subductions and faults. Spreading oceanic
ridges are located in all the
major ocean basins of the world. This will
occur when 2 plates move apart from
one another causing cracks to form. While
this is happening the cracks will fill
with molten lava and the new crust
will expand the sea floor. These occurrences
being indigenous to oceanic
crust will constitute the largest mountain range on
the planet. Subduction
zones are the 2nd types of plate boundary. These are
formed when plates come
together and overlap. If we compare subduction to
spreading ridges, they
differ greatly. Subduction will destroy the plates, where
spreading ridges
will constantly create new ones. Earthquakes traveling from
depths of 370
miles will also effect subduction zones. Spreading ridges will
only be
altered by very shallow earthquakes originating only 44 miles deep.
Two
unique geological structures are formed from the Subduction of the ocean
floor,
trenches and andesitic volcanoes. This brings us to the third and last
plate
boundary, transform faults. Transform faults will run across
continent's ocean
floor and combine with oceanic ridges, transforming fault
pieces to create a
long rectilinear zigzag. While subduction zones are almost
always arcuate in
shape. The transform fault will simply be the connector
between two different
kinds of active plate boundaries. An example of the
most well known and studied
fault is the San Andreas Fault located of the
coast of California. 11. The
origin of volcanoes: Hot spots, can be found on
plate boundaries or inside the
plates. The hot spot is a place deep inside
the Earth that begins to form molten
lava from extreme heat conditions. It
will quickly rise up, pushing and melting
its way to the surface resulting in
a volcano. Because of the constant moving of
the plates, the volcano will be
carried away from the hot spot and become
dormant. This process will repeat
itself, forming a never-ending row of
volcanoes. 12. The crust, being the
absolute outer layer of the Earth is made up
of the every day surface rocks
like granite, basalt, limestones and so on. The
mantle is made up of dark,
dense rocky materials that are denser then the
above-mentioned crust. The
mantle will take up the largest part of the Earth's
interior, lying
in-between the crust and the core. The lithosphere lies in the
upper 100
kilometers of the Earth's body. The lithosphere takes a much more
rigid abuse
because of the surrounding temperature being much under the melting
point.
The lithosphere zone is also responsible for creating the rigid plates
called
lithospheric plates. Lying directly under the lithosphere zone is
the
asthenosphere. Located in the low velocity zone, it's constantly exposed
to
extreme borderline melting temperatures. This results in making this zone
very
soft and equally weak. 13. Scientists will use paleomagnetism to study
the
Earth's magnetic field found inside rocks. Acting like a compass, the
northern
magnetic field will cause cooling lava to freeze in the direction of
the
magnetic field. The Earth's magnetic field has been known to switch
directions
(magnetic polarity reversals). When this occurs it will only take
a few thousand
years to flip to the opposite position. Magnetic reversals are
a great tool for
measuring the movements of the oceanic plates. Sea floor
spreading will be
altered dramatically, depending on the current direction of
the magnetic field.
When the magnetic field is in its normal direction,
the oceanic floor spreading
will be magnetized normally. But if the magnetic
field is reversed, newly formed
oceanic floor will become reversely
magnetized. If magnetic fields in the sea
floor match, it will create a
smooth and flat surface. So combining
paleomagnetism and sea floor spreading
allows scientists to track the exact
movement of the plates on both sides of
the ridge. 14. In the last 250 million
years there have been significant
movement and change in the Earth's major
crustal plates, resulting in
continents moving. Bringing us to the Triassic
period, Asia had been mostly
put together and a number of continental collisions
caused mountains to form,
creating the now Appalachians. During the middle of
the Jurassic period,
Pangea (all land) had been formed. Pangea was one giant
continent surrounded
by a world of ocean. During the ladder half of Jurassic,
Pangea began to
move, break apart and rotate clockwise, destroying land so that
India and
Asia were now separated. During these changes the North Atlantic began
to
open up and the ocean floor we see today began to show itself. Subduction
of
the ocean floor under the west coasts of North and South America created
what we
know now as the Andes and the Sierra desert of Nevada and California.
Coming to
60 million years ago, Australia had split from Antarctica going
south while
Antarctica traveled north. To this day Africa still continues
to move north,
while Italy breaks through Europe creating the Alps. And
continental collisions
by India and Asia are still occurring, forming the
Himalayas higher and higher.
15. The impact and strength of an earthquake
can be measured in 2 different
ways. The first most well known method is the
Richter scale. The Richter method,
being a 1-10 scale is based on the
measurement of the ground shaking of a
certain point located a distance from
the actual earthquake. The Richter scale
is only a rough indicator of the
absolute total energy released from the
earthquake. This brings us to the
Modified Mercalli Intensity scale that unlike
the Richter; it does not
involve the expensive high-tech equipment used for the
Richter method.
The Mercalli method is to observe change and interview witnesses
involved in
the earthquake and then constructed in a special scale from I-XII, I
being
"not felt except by very few" to XII "total damage and
catastrophic
destruction". 16. Rifts, Subductions, and Faults are types of
crustal plate
boundaries that react similar to earthquakes or volcanoes. Like
volcanoes,
rifts are created by plates pulling away causing cracks to fill up
with lava,
causing new floor to reveal itself. Faults are fractures in rocks
that have
been displaced on both sides facing each other. The fault is also a
cozy home
for earthquakes. Subductions will also cause earthquakes when plates
run into
one another and overlap. As a result of the plates overlapping the
under
crust will bend under into the mantle. Unit IV 17. In the event of
an
earthquake, vibrations will be produced, causing seismic waves. There are
two
types of waves that have the ability to travel deep within the body of
Earth.
First is P waves that are the fastest moving waves, resulting in
the first wave
to be recorded. To move as fast as they do, they must have the
ability to
penetrate solids, liquids and gases. S waves will travel slower in
a snake-like
pattern. Unlike P waves, the S wave cannot pass through liquids
or gasses
because of it depending on the medium's resistance to sideways
deformation. 18.
Knowing these facts about seismic waves enables us to
learn a great deal about
the Earth's core. Because that we know S waves are
unable to penetrate liquid or
the core-mantle boundary, we can assume its a
liquid substance. Modern
seismology can also detect how long it takes waves
to travel from point a to
point b along the surface. From that information,
it's now possible to create a
picture of the Earth's interior. Noticing the
velocity increase in P waves
entering the inner core leads us to believe its
solid. 19. The Earth's
structural blue prints simply show this: We start with
the ground we live on and
travel below the thin crust to rocks like granite
and other well-known rock
types. Then we reach the mantle containing very
dense materials like olivine,
garnet, proxenes, and spinel. The mantle is
immense in size and takes up 83% of
the Earth's volume. As we travel halfway
to the center, we run into the core.
The core consists of molten iron and
sulfur which takes a white-hot form. This
brings us to the free-floating huge
iron ball, measuring 1,500 miles across. 20.
When liquids and gasses of
extreme high temperature travel to a cooler location,
they will begin to
transform and take the form of a solid-state. Scientists
believe the
convective motions of the asthenosphere inside the mantle cause the
plates to
shift on the Earth's surface. Unfortunately at present day, scientists
can
not be certain of the effect mantle convection have on the moving of
tectonic
plates.