The layers of earth are based on what two sets of characteristics? Before delving into the specifics of plate tectonics, it is necessary to have a solid foundational knowledge of the several strata that make up the planet.
The majority of what we know about what is under the surface is cobbled together from theoretical models, the analysis of seismic wave data, and the examination of meteorite materials. The amount of firsthand knowledge about what lies below the surface is quite restricted. In a broad sense, the Earth may be sectioned up into strata determined by the chemical make-up and physical features of each layer.
There is no doubt that the earth is made up of an infinite number of different element combinations. Temperature and pressure are the two primary contributors to the formation of three unique chemical layers, and this holds true regardless of the components that are being used.
The crust is the most superficial chemical layer and the one that we are located on at the present time. There are two distinct crusts to choose from. Granite is a good analogue for the comparatively low density and chemistry that characterise continental crust.
Oceanic crust has a composition comparable to that of basalt, which contributes to its relatively high density, particularly when it is ancient and cold. The top layers of the crust are more fragile than deeper ones. They become more ductile when they are exposed to greater temperatures and pressures, which occur deeper into the crust.
Materials that are ductile are similar to putty or soft plastics in that they deform when force is applied to them. Materials that are brittle are analogous to solid glass or pottery in that they shatter when subjected to force, particularly when that force is delivered rapidly. Generally speaking, earthquakes take place in the upper crust and are brought on by the fast movement of relatively fragile minerals.
Seismic velocity is a measurement that determines how quickly earthquake waves move through solid materials. The base of the crust is characterised by a significant rise in seismic velocity. Andrija Mohorovii (pronounced mo-ho-ro-vee-cheech; audio pronunciation) identified this zone in 1909 and gave it the name the Mohorovii Discontinuity, or Moho for short.
He did so after researching the pathways an earthquake wave travels in his home country of Croatia. The enormous chemical changes that exist between the crust and the mantle are the root cause of the shift in wave direction and speed.
The Moho may be discovered around 5 kilometres below the surface of the seas, where it is located. Approximately 30–40 kilometres below the surface, it may be found buried under the continents. The Moho depth of the continents is known to be doubled in proximity to certain mountain-building processes known as orogenies.
The xenolith is perched on a basalt rock in its current location. It resembles a pyramid in that it has three sides, however one of those sides is significantly modified to iddingsite.
Figure 2.2.3: This mantle peridotite xenolith contains olivine, which is chemically transforming into the brown pseudo-mineral iddingsite via the processes of hydrolysis and oxidation to become iddingsite.
Iddingsite is a combination of water, clay, and iron oxides. The side of the rock that has been affected more by the surrounding environment has been exposed to it for a longer period of time.
Below the crust and above the core is where you’ll find the mantle. It starts at the bottom of the crust and goes down to a depth of roughly 2,900 kilometres, making it the most extensive chemical layer in terms of volume. Although much of the information about the mantle comes from the study of ophiolites and xenoliths, seismic wave analysis is where the majority of the knowledge about the mantle comes from.
Ophiolites are fragments of the mantle that have made their way up through the crust and are now found on the ocean bottom. Magma transports xenoliths to the surface of the Earth, where they are then transported to the surface by volcanic eruptions.
The majority of xenoliths are composed of peridotite, which belongs to the ultramafic group of igneous rocks (see Chapter 4 for explanation). Because of this, scientists have a working hypothesis that peridotite makes up the majority of the mantle.
Iron, nickel, and maybe some oxygen make up the majority of the Earth’s core, which is composed of both liquid and solid layers. The core of the Earth contains both of these types of layers. In the year 1990, researchers examining seismic data made the first discovery of this most deepest chemical layer.
They came to this conclusion by using a combination of hypothetical modelling, astronomical understanding, and hard seismic evidence. They found that the core is mostly composed of metallic iron.
Scientists who analyse meteorites, which often contain more iron than the rocks found on the surface, have put up the hypothesis that the planet was created from material that came from space.
They think that the liquid component of the core was generated when the iron and nickel sunk into the heart of the planet, where it was subjected to extreme pressure and turned into a liquid state.
Because of the different ways in which different layers react to pressure, the planet may also be divided into five unique physical layers.
There is substantial overlap between the chemical and physical designations of layers, particularly near the border between the core and the mantle; nonetheless, there are major distinctions between the two systems overall.
The word “stone” comes from the Greek word “lithos,” and the lithosphere is the outermost layer of the Earth’s crust. Oceanic and continental kinds are distinguished from one another in this regard.
The oceanic lithosphere is thin yet more robust than other lithospheres. In new plates discovered at mid-ocean ridges, its thickness is close to nil, but in most other areas it averages out to be around 140 kilometres thick.
In general, the continental lithosphere is thicker, and particularly at deeper levels, it has a far higher degree of plasticity. The thickness of it varies anywhere from 40 to 280 kilometres. There are discontinuities in the lithosphere. Plates are used to denote the individual sections that make up the whole.
When two plates collide and continue to move in relation to one another, this is known as a plate boundary. Plate borders are the locations where we see the processes of plate tectonics in action, such as the formation of mountains, the initiation of earthquakes, and the production of volcanic activity.
The layer that lies directly under the lithosphere is known as the asthenosphere. The prefix astheno- refers to a lack of strength, and the ability to move is the asthenosphere’s most defining characteristic. This layer moves and flows owing to convection currents formed by heat coming from the earth’s core source.
This layer is mechanically weak, therefore it is moved and flowed by these currents. In contrast to the lithosphere, which is made up of several plates, the asthenosphere is a comparatively uninterrupted layer.
By measuring seismic waves that go through the stratum, the researchers were able to come to this conclusion. Temperature plays a factor in determining the depth at which one may find the asthenosphere. It is more likely to be found closer to the surface of the planet along mid-ocean ridges, but it is considerably more likely to be found far deeper behind mountains and in the cores of lithospheric plates.
The atoms are organised in this fashion.
Figure 2.2.6: General perovskite structure. It is believed that perovskite silicates, such as bridgmenite ((Mg,Fe)SiO3), are the primary component of the lower mantle, which would make perovskite the most prevalent mineral in or on Earth.
When compared to the asthenosphere, the mesosphere is much more rigid and immovable. It is also frequently referred to as the lower mantle.
The mesosphere is characterised by very high pressures and temperatures due to its location between about 410 and 660 kilometres below the surface of the planet. These harsh circumstances give rise to a transition zone in the upper mesosphere, which is characterised by the constant transformation of minerals into a variety of shapes known as pseudomorphs.
Changes in seismic velocity and occasionally physical obstacles to movement are what scientists use to pinpoint the location of this zone. Once you go beyond this zone of change, the mesosphere continues to be rather consistent all the way down to the core.
The only other layer in the Earth that consists completely of liquid is the outer core. It begins at a depth of 2,890 kilometres and continues to a distance of 5,150 kilometres, which gives it a thickness of around 2,300 kilometres.
In 1936, the Danish geophysicist Inge Lehmann studied seismic data and was the first person to verify the existence of a solid inner core inside a liquid outer core. He did this by becoming the first person to prove the existence of an inner core. The thickness of the liquid outer core is around 2,300 kilometres, whereas the thickness of the solid inner core is approximately 1,220 kilometres.
The planet’s molten outer core is of paramount significance to the upkeep of a breathable atmosphere as well as other climatic variables that are suitable to the existence of life. It is believed by scientists that the circulation of molten iron and nickel inside the earth’s outer core is responsible for producing the earth’s magnetic field.
If the planet’s outer core were to suddenly cease circulating or become solid, the loss of the planet’s magnetic field would cause the planet to lose the gases and water that are necessary for life. This is what took place on Mars, and it is still taking place today.
At passive edges, the plates do not move; instead, the transition from the continental lithosphere to the oceanic lithosphere results in the formation of plates that include both kinds.
Oceanic lithosphere and continental lithosphere may both be components of a tectonic plate, with the two types of lithosphere being joined by a passive margin. An example of a passive margin is seen along the eastern shores of both North and South America.
Such regions as the western coastlines of North and South America are examples of active margins. Active margins are locations where the oceanic and continental lithospheric tectonic plates meet and move relative to each other.
The frictional drag that is formed between the plates as well as the variances in plate densities are the root causes of this movement. The movement of tectonic plates along active edges is responsible for the vast majority of mountain-building events, earthquake activity, and active volcanism that occur on the surface of the Earth.
In a model that has been simplified, there are three different classifications of tectonic plate borders. Plates may move closer to one another at certain limits, which are known as convergent boundaries. The plates move apart at the borders where they divide. At the boundary between transformations, the plates glide past one another.
What are the two different groups of features that the strata of the earth are founded on? Composition on a chemical level and physical characteristics
According to the make-up of The rocky crust, the mantle (which is formed of rock-forming elements), and the iron-nickel core are the three components that make up the earth.
Create a hierarchy of the Earth’s layers, moving from the interior to the surface, depending on the physical attributes and characteristics of each layer. You just studied 7 terms!
There are three distinct layers that make up the earth, and they are the crust, the mantle, and the core. This is the outermost layer of the planet, and it is composed of solid rock composed mostly of basalt and granite.
Oceanic crust and continental crust are the two categories of crust. Oceanic crust is more compact, has a lower thickness, and is predominately made up of basalt.
The layers of the Earth give geologists and geophysicists with clues about how the Earth evolved, about the layers that make up other planetary bodies, about the source of the Earth’s resources, and about many other things.
The crust, the mantle, and the core are the three distinct layers that make up the earth. This is the outermost layer of the planet, and it is composed of solid rock, the majority of which is basalt and granite. Oceanic crust is distinct from continental crust in a number of ways.
The mantle is a solid/plastic material, the outer and inner cores are both liquid, and the inner core is solid. This is because to the rise in temperature and pressure that occurs with increasing depth, as well as the difference in the respective melting points of the various layers (nickel–iron core, silicate crust, and mantle).
The structure of the Earth may be broken down into four separate layers, beginning with the core. In order from the deepest to the shallowest, they are the crust, the mantle, the inner and outer cores, and finally the crust.
No one has ever personally investigated any of these strata, with the exception of the crust. In point of fact, the human race has only ever delved a little more than 12 kilometres deep (7.6 miles).
Chemical make-up and physical characteristics may each be used as a dividing factor for stratifying the Earth into its many portions and strata. There are three distinct chemical layers, which are the crust, the mantle, and the core, as well as five distinct physical layers, which are the lithosphere, the asthenosphere, the mesosphere, the outer core, and the inner core.