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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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”.
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.
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.
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.
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.
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.