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Anxiety: a guide to proper usage
Breakdown of the presentation by individual slides:
Slide 2: What is the Earth’s core made of?
The Earth’s core is located at the center of the globe and is primarily made up of iron and nickel. It may also contain small amounts of other elements like sulfur or gold. Surrounding the core is a semi-liquid mantle comprised mainly of silicon and magnesium compounds. Above the mantle is the lithosphere, a thin and rigid crust that is home to all known forms of life.
Slide 3: How deep is the core of the Earth?
Unraveling the mysteries of the Earth’s core poses many difficulties, but determining its depth is not one of them. The core starts just 2,900 km below sea level, with the Earth’s radius being 6,371 km.
When you move towards the center of the Earth, the pressure and heat both increase. As you descend into the planet, the temperature rises by about 25 degrees Celsius per kilometer. For example, at a depth of 4 kilometers in a mine, the temperature is around 60 degrees Celsius. At the bottom of the deepest well, which is over 12 kilometers deep, the temperature reaches 180 degrees Celsius. The outer layer of the mantle can reach temperatures of about 1000 degrees Celsius. In the Earth’s core, the temperature is even more extreme, at around 6000 degrees Celsius, which is slightly lower than the surface of the Sun. It’s interesting to note that the Mponeng mine, located in the Republic of South Africa, is the deepest mine in the world.
Slide 5: What are the constituents of the Earth’s core?
The Earth’s core consists of two distinct layers, with a separation known as the Lehman gap. The outer layer is primarily composed of a liquid alloy made of iron and nickel, which is heated to temperatures ranging from 4500 to 5500 degrees Celsius. On the other hand, the inner core is predominantly made up of iron and is spherical in shape, with a diameter of 1,220 kilometers. Geophysicists describe the Earth’s core as a plasma ball that exhibits solid-like behavior due to the immense pressure it experiences.
Slide 6: Radius and Mass of Earth’s Core
The Earth’s core has a diameter of 3,740 kilometers – that is twice the size of the Moon and slightly larger than Mercury. Despite its relatively small size, the mass of Earth’s core is approximately 1.85 trillion metric tons – which is nearly one-third of the planet’s total mass. This suggests that it consists of heavy elements, although if these were highly radioactive, it would have been impossible for life to exist on Earth. Geologists propose that the Earth’s core is primarily composed of iron.
Slide 7: Is the Earth’s core getting bigger?
With the cooling of the Earth, the inner core thickens and expands. It gradually expands at a rate of 1 millimeter per year as its outer layers solidify and transform into the mantle. This expansion also occurs because of the heat escaping from the mantle into the Earth’s crust at the collision zones of tectonic plates. This cooling process is extremely slow, and it is likely that the solar system will cease to exist before the Earth’s core fully solidifies.
Slide 8: A ball of red-hot rock
The Earth’s core predates the planet itself and its temperature suggests that it was once a glowing ball of rock during the early stages of Earth’s formation. The intense radioactivity and high temperatures associated with the formation of the solar system caused the Earth to heat up to 1,500 degrees Celsius, which is the melting point of iron. This process took place over a span of 500 million years. As a result, lighter elements like silicates and oxygen compounds were able to rise to the surface, while droplets of nickel and iron were pulled downwards by gravity. This is how the Earth’s core came into existence.
Slide 9 – The Earth’s interior
How can we investigate the deepest layer of the Earth?
Our understanding of Earth’s core is often attributed to seismic activity. The intense pressure in the core causes molecules to arrange themselves in a tightly packed crystal structure, particularly with iron. This unique composition enables the core to effectively transmit seismic waves, or vibrations. The speed and frequency of these vibrations vary based on factors such as pressure, temperature, and the Earth’s chemical makeup. The fact that the Earth’s interior can conduct certain vibrations, similar to liquids, serves as evidence that it has a liquid nature.
10 slide Meteorites offer valuable insight into the chemical makeup of Earth’s core.
Meteorites also provide important information about the composition of Earth’s core. These celestial objects, which originate from the asteroid belt located between Mars and Jupiter, likely formed around the same time as our planet. By studying meteorites, scientists can gain a better understanding of the formation of our solar system and the core of our planet.
The core of Earth remains largely mysterious, but it plays a vital role in supporting life on our planet. While direct study of Earth’s core is not possible, its influence on our well-being and the overall health of our planet is undeniable.
Discovering the inner composition of our planet. Study the makeup of the Earth: its crust, core, mantle, the chemical elements that form it, the history of exploration, and the science of geology.
The Earth contains more than meets the eye. If we were able to slice it in half, we would be astounded by what we find. While we search for new worlds, there is still so much to uncover about our own.
Fortunately, seismology has allowed us to uncover the Earth’s structure and understand its various layers. Each layer possesses unique properties, characteristics, and compositions, all of which play a role in the Earth’s dynamic processes. So, what exactly is the Earth composed of?
Contemporary theory
The planet’s interior is characterized by differentiation, meaning it is composed of various layers. By removing one layer, we can access the next layer, each with its unique temperature and chemical composition, similar to other planets.
Our comprehension of the planet’s layers is derived from seismological monitoring. This method entails studying sound waves generated by earthquakes and analyzing how their velocity is affected as they pass through different layers. Variations in seismic velocity result in refraction.
A representation of Earth’s core in the form of a flat disk with continents and an icy wall in Antarctica
These models are utilized in conjunction with alterations in gravitational and magnetic fields, as well as experiments with crystalline solids that replicate the extreme pressure and temperature found deep within the planet.
Investigation
Since ancient times, humanity has been endeavoring to comprehend the structure of the Earth. The initial endeavors were not of a scientific nature, but rather encompassed legends and myths centered around divine intervention. Nevertheless, several hypotheses became prevalent within the populace.
You may be familiar with the notion of a flat Earth. This belief was held within Mesopotamian culture, where the planet was depicted as a flat disk encompassed by ocean. The Mayans similarly conceived of it as flat, but with four jaguars stationed at the corners to support the sky. The Persians envisioned a mountain in space, and the Chinese imagined it as a four-sided cube.
In the 6th century BC, the Greeks started to gravitate towards a rounded form, while by the 3rd century BC, the notion of a spherical Earth was gaining traction and the first evidentiary support. Simultaneously, scientists began delving into geological studies and philosophers started contemplating minerals and metals.
Edmund Halley’s illustration of the Earth, depicted as concentric spheres
However, the real paradigm shift did not occur until the 16th and 17th centuries. In 1692, Edmund Halley proposed the Hollow Earth theory. He posited that there exists a cavity, or rather a central core, with a thickness of 800 kilometers.
An air gap exists between these spheres. In order to avoid any frictional effects, the inner sphere must be held in place by gravity. The model showcased two concentric shells surrounding the core, with their diameters corresponding to those of Mercury, Venus, and Mars.
The rise in significance of mining during the 17th and 18th centuries, particularly in the search for valuable metals, brought about a revolution in the field of geology.
In 1774, Abraham Werner introduced a comprehensive classification system for identifying specific minerals based on their outward features.
In 1741, the initial publication on geology emerged at the French National Museum of Natural History. A decade later, the term “geology” became widely recognized and used.
In the 1770s, the focus of scientific research shifted towards chemical analyses. A significant objective was to investigate the historical occurrence of liquid flooding at various locations (known as the Flood). By the 1780s, there were individuals who held the belief that these layers were not a result of water, but rather of fire. These supporters were referred to as plutonists. According to their perspective, the formation of the planet occurred through the gradual solidification of molten masses, a process that took place over an extensive period of time. Consequently, their theory suggested that the age of the planet far exceeded the timeline described in the Bible.
The famous ship Beagle in the beautiful Galapagos Islands.
During the 19th century, the field of geology experienced significant developments due to the influence of the Industrial Revolution and the introduction of the stratigraphic column. This column enabled scientists to arrange rock formations in the order of their appearance over time, providing valuable insights into geological history. Additionally, researchers embarked on voyages to expand their knowledge and compare findings from various locations. Among these fortunate explorers was Charles Darwin, who was recruited by the captain of the Beagle.
During his expedition, Darwin made remarkable discoveries of giant fossils that sparked his interest in geology. These findings, combined with his theories on the causes of extinction, ultimately led to the publication of his groundbreaking work, “On the Origin of Species,” in 1859.
Earth’s tectonic plates
Scientists expanded their understanding and developed geological maps of the Earth. They began to calculate the age of the Earth in millions of years, rather than thousands. However, advancements in technology played a key role in challenging longstanding beliefs.
The 20th century witnessed the introduction of radiometric dating. At that time, it was believed that the age of the Earth could be up to 2 billion years old. In 1912, Alfred Wegener proposed the theory of continental drift, suggesting that all continents were once a single landmass. This idea was later confirmed through geological analysis of samples.
The Permian Period (300-20000 million years ago) was characterized by the existence of Pangaea, a single continent.
The study of the ocean floor led to the development of the theory of plate tectonics. Geophysical data revealed the lateral movement of continents, with the oceanic crust being younger than the continental crust.
Seismology, the study of earthquakes and seismic waves, played a crucial role in the 20th century in understanding the Earth’s composition and reaching its core.
The Apollo 11 spacecraft captured an image of Earth from its position near the moon.
In 1926, Harold Jeffis proposed that the core of the Earth is in a liquid state. In 1937, Inge Lehmann expanded on this idea and suggested the presence of a solid inner core within the liquid core.
Structure of the Earth
The Earth’s composition can be analyzed both mechanically and chemically. The mechanical approach focuses on the different states of matter, including the lithosphere, asthenosphere, mesosphere, and the outer and inner core. On the other hand, the chemical method categorizes the Earth’s layers into the crust, mantle, and core.
The inner core is solid, while the outer core is in a liquid state. The lower mantle experiences high pressure, resulting in a lower viscosity compared to the upper mantle. These variations in composition and state are a result of the various geological processes that have occurred over the course of the Earth’s 4.5 billion year history. Let’s examine the internal structure of our planet in more detail.
The outer layer
The crust is the cooled and frozen outer layer of the planet. It covers a distance of 570 km and makes up just 1% of the total volume of the planet.
The narrower sections consist of the oceanic crust that lies beneath the ocean basins (5-10 km), while the denser portions make up the continental crust. The lithosphere, which extends 200 km, encompasses the upper part of both the mantle and crust. The majority of the rock was created approximately 100 million years ago.
Upper mantle
Comprising 84% of the total volume, the upper mantle generally behaves as a solid, but occasionally exhibits properties of a viscous liquid. It begins at the “Mohorovicich Surface” – 7-35 km deep, and extends down to 410 km.
The movement within the mantle is reflected in the motion of tectonic plates and is driven by heat emanating from the depths. This process is responsible for earthquakes and the formation of mountain ranges.
The temperature increases by 500-900°C. The layer between 410-660 km in depth is considered a transition zone.
Lower mantle
The lower mantle, located at a depth of 660-2891 km, can reach temperatures of up to 4000°C. However, the immense pressure in this region restricts viscosity and melting. This layer remains largely unknown, but it is believed to exhibit seismic homogeneity.
The outer core
The outer core forms a liquid shell with a thickness of 2300 km and extends to a radius of 3400 km. In this region, the density significantly increases, ranging from 9900-12200 kg/m3. The core is composed primarily of iron (80%), along with nickel and other lighter elements. Despite its composition resembling that of the inner core, the absence of high pressure prevents it from solidifying. The temperature in the outer core is approximately 4030°C.
The liquid core’s temperature and turbulence generate a dynamo effect, which influences the Earth’s magnetic field.
The Earth’s Core: Composition and Characteristics
The Earth’s core is primarily composed of iron and nickel, which span a radius of 1220 km. It is a dense region, with a density ranging from 12600-13000 kg/m 3 , indicating the presence of heavy elements such as platinum, gold, palladium, tungsten, and silver.
Artistic interpretation of the Earth’s core
The temperature in this region reaches a scorching 5400°C. So, why do the metals remain in a liquid state? The answer lies in the incredibly high melting point and pressure. The core is not tightly connected to the solid mantle, which is why it is believed to rotate faster than the planet itself.
Scientists also theorize that the inner core consists of layers separated by a transition zone with a thickness ranging from 250 to 400 km. The innermost layer is estimated to have a diameter of 1180 km. Studies suggest that the core expands by 1 mm per year, showcasing its dynamic nature.
The deepest and hottest layer on the planet is known as the Earth’s core. It is a solid and spherical region within the Earth.
The Earth is composed of three significant layers, which are referred to as the geosphere (solid), the hydrosphere (comprising of liquids in gaseous or solid states), and the atmosphere (consisting of different gases).
Nevertheless, the core of the Earth is composed primarily of metals, specifically iron and nickel, with smaller amounts of sulfur and oxygen. It surpasses the size of Mars and accounts for approximately 15% of the Earth’s total volume.
A plethora of information regarding the Earth’s core has been acquired by researchers through the examination of volcanic rocks. These rocks undergo a process of solidification after being expelled from the Earth, gradually cooling over time.
Remarkably, scientists have made the groundbreaking discovery that the Earth’s core is currently in the process of formation. The solidification process commenced roughly one to two million years ago, suggesting that approximately three billion years ago, the Earth’s core was in a liquid state.
The structure of the Earth’s core
The Earth’s core is made up of two sections: an outer core and an inner core.
The outer core
Situated approximately three thousand kilometers below the Earth’s surface, the outer core is a fluid consisting of a combination of iron and nickel. It has a thickness of around 2,300 kilometers.
This core maintains a temperature of roughly 5,000 degrees Celsius, which is not sufficient to solidify its liquid composition.
Scientists hypothesize that the outer core is responsible for various magnetic and electrical phenomena observed on Earth.
Central nucleus
This is the most scorching spot on the planet, with temperatures fluctuating between 5,000 and 7,000 degrees Celsius.
It is constructed of compact iron; nevertheless, it is capable of enduring extreme temperatures and pressure without liquefying. Its estimated diameter is around 1,200 kilometers.
This nucleus was unveiled in 1936 by Danish seismologist Inge Lehmann. After numerous analyses and calculations, scientists have ascertained that the central nucleus exhibits a rotational movement and that it spins one degree faster than the surface.
Some of the primary features of the Earth’s core include:
- The core is the deepest and hottest part of the planet.
- Compared to other layers of the Earth, it formed at a slow pace.
- The core’s size surpasses that of Mars.
- It consists of two cores, an outer one that is liquid and an inner one that is solid.
- Mainly composed of iron and nickel.
- It has an influence on and interacts with various magnetic phenomena on Earth.
Around our planet: its origins, composition, and beyond
Isaac Newton, an English scientist who lived three centuries ago, made calculations about the density of the Earth and concluded that it is twice as dense as its surface rocks. This led him to believe that the interior of the Earth must consist of much denser materials. Since Newton’s time, our understanding of the Earth’s interior has greatly improved, but his estimation of its density remains largely unchanged. Seismic surveys have provided us with valuable information about what lies deep within the Earth.
Planet Earth consists of three primary layers: the delicate and thin crust, the mantle, and the core. Despite the fact that the core and mantle have similar thicknesses, the core only comprises 15 percent of the Earth’s overall volume, while the mantle accounts for 84 percent. The remaining 1 percent is occupied by the crust. Scientists continuously enhance our understanding of the Earth’s structure and chemical composition through laboratory experiments involving rocks subjected to high pressure and the analysis of earthquake data using computer technology.
Earth’s Crust: A Comprehensive Study
The Earth’s crust, being easily accessible to us, has undergone extensive geological research. As a result, we have gathered a wealth of information about its structure and composition, surpassing that of the mantle and core. Within the crust, intricate formations emerge as rocks are redistributed and deposited in layers through various geological processes, such as volcanic eruptions, lava intrusion, erosion, compaction of rock particles, solidification, and recrystallization of porous rock.
Measuring relatively thin, the crust varies in thickness, ranging from 4-10 km beneath the oceans to 30-70 km beneath the continents.
Throughout most of Earth’s history, about twelve plates consisting of continents and ocean basins have undergone extensive movement across the Earth’s surface due to the process of plate tectonics. At the edges of these plates, earthquakes occur and volcanoes can be found. The collision of these plates can result in the formation of mountains, such as the Himalayas, which is the tallest range in the world. These tectonic plates include the Earth’s crust and a portion of the upper mantle. They move at a very slow pace within the hot zone of the upper mantle, typically only a few centimeters per year, which is even slower than the rate at which fingernails grow.
The boundary between the Earth’s crust and mantle is referred to as the Mohorovičić (or Moho) discontinuity, named after the Croatian scientist Andrija Mohorovičić, who first discovered it. Although this boundary has never been directly observed, it can be detected due to a significant increase in the speed of seismic waves.
There is a hypothesis that the reason for this acceleration in speed at Moho is a alteration in rock compositions. One suggestion is to execute drilling operations to reach the Moho and establish the demarcation line between the granite and basalt strata. A Soviet well on the Kola Peninsula managed to be drilled to a depth of approximately 12 kilometers. However, the well did not successfully breach the granite layer. The expenses for drilling escalate significantly with depth, thus the drilling operation was terminated in 1994. It is improbable that we will achieve penetration of the Moho in the foreseeable future.
Mantle
The Mantle
The Earth’s Mantle
The mantle is a layer of the Earth between the crust and the core. It is a thick, solid layer that makes up about 84% of the Earth’s volume. The mantle is composed mostly of silicate rocks and is divided into two main regions: the upper mantle and the lower mantle.
The upper mantle is closest to the Earth’s crust and is made up of rigid, solid rock. It is also the layer where most of the Earth’s earthquakes and volcanic activity occur. The lower mantle is located beneath the upper mantle and is hotter and more fluid. It is composed of semi-solid rock that flows very slowly over long periods of time.
The mantle plays a crucial role in the movement of tectonic plates, which are large pieces of the Earth’s crust that slowly move and interact with each other. The upper mantle is responsible for the convection currents that drive plate tectonics. These currents are caused by the heat from the core, which heats up the mantle and causes it to rise. As the mantle rises, it cools and sinks back down, creating a continuous cycle of movement.
Overall, the mantle is a dynamic layer of the Earth that plays a vital role in shaping the planet’s surface and influencing geological activity. It is a complex and fascinating part of our planet that scientists continue to study and learn more about.
In the lower mantle, which is situated beneath the transition zone, there are relatively uncomplicated iron and magnesium silicate minerals that progressively transform into highly compacted varieties as the depth increases. As the mantle transitions into the core, there is a distinct reduction of about 30 percent in the velocity of seismic waves, accompanied by a noteworthy increase of approximately 30 percent in density.
The heart
The heart of our planet is the incredibly hot and dense core. Nestled beneath a delicate and cool crust, the core is a mostly solid and spherical center. Located approximately 2,900 kilometers below the Earth’s surface, the core has a radius of about 3,485 kilometers.
The core, which was the first internal structural component to be identified, was uncovered in 1906 by Irish geologist R. D. Oldham. While studying seismograms of an earthquake in Guatemala, Oldham made this groundbreaking discovery. It played a crucial role in explaining Newtonian calculations regarding the density of the Earth.
The Earth’s core is younger than the planet itself. When the Earth was created approximately 4.5 billion years ago, it was a uniform sphere made of heated rocks. The combination of radioactive decay and residual heat from the collision and compression of space rocks caused the sphere to heat up even more. After approximately 500 million years, the temperature on our youthful planet reached the melting point of iron, which is around 1538 °C. This significant moment in Earth’s past is known as the iron catastrophe.
The iron catastrophe led to an acceleration in the movement of Earth’s molten rocks. Lighter materials such as silicates, water, and air were able to remain near the surface, giving rise to the early mantle and crust of the planet. On the other hand, heavier metals like iron and nickel were pulled towards the center of the Earth by gravitational forces, forming the foundation of the early core. This significant process is known as planetary differentiation.
The increase in temperature of rocks within a specific section of the Earth’s layers can be described by a physical quantity called the geothermal gradient, measured in degrees Celsius. It represents the change in temperature per unit of depth. Typically, the geothermal gradient ranges from 0.5-1 to 20 degrees Celsius, with an average of around 3 degrees Celsius per 100 meters. The Earth’s core acts as the destination for the geothermal gradient.
The Kola ultra-deep well played a significant role in studying the geothermal gradient. Initially, calculations were based on the assumption that the gradient would be 10 °C per kilometer, as the plan was to drill 15 kilometers. This meant that the expected temperature at the calculated depth would be approximately +150 °C. However, it was discovered that the gradient of 10 °C/km only held true for the first three kilometers. After that, the gradient started to increase, resulting in a temperature of 120 °C at a depth of 7 km, 180 °C at 10 km, and 220 °C at 12 km. Ultimately, it was determined that at the intended depth of 15 km, the temperature should reach +280 °C.
In the core, the main sources of heat are the decay of radioactive elements, residual heat from planetary formation, and the release of heat as the liquid outer core solidifies near its boundary with the inner core.
The elements that can dissolve in iron and are found in the core are known as siderophiles. Due to their scarcity in the Earth’s crust, many siderophiles are considered “precious metals”. Siderophile elements encompass gold, platinum, cobalt, iridium, osmium, rhenium, palladium, rhodium, ruthenium, molybdenum, and nickel.
Sulfur is another significant element in the Earth’s core, comprising 90% of its sulfur content. The discovery of such a large quantity of sulfur provides an explanation for a geological enigma: if the core consisted mostly of NiFe, why isn’t it heavier? Geologists hypothesized that lighter elements like oxygen or silicon might be present in the core. However, the abundance of sulfur, another relatively light element, resolves this mystery.
Although it is widely known that the core of our planet is the hottest part, determining its exact temperature is an extremely challenging task. The temperature within the core is influenced by various factors, including pressure, the Earth’s rotation, and the varying composition of elements present. Typically, the core experiences temperatures ranging from approximately 4400 °C to 6000 °C.
Comprising of two layers, the core consists of an outer core, which lies adjacent to the mantle, and an inner core. The boundary separating these regions is referred to as the Bullen gap.
Outer Core
The outer core, with a thickness of approximately 2,200 km, primarily consists of liquid iron and nickel. The NiFe alloy within the outer core is highly heated, ranging between 4500 and 5500 °C.
The liquid metal found in the outer core exhibits extremely low viscosity, making it easily deformable and malleable. This region is characterized by vigorous convection movements.
The Earth’s magnetic field is generated and sustained by the molten metal in the outer core. The Bullen Gap, located in the core, is the hottest region with temperatures soaring up to 6000 °C – equivalent to the scorching surface of the Sun.
Definition of the Earth’s Core
The Earth’s core is a dense, hot sphere primarily composed of iron. It measures approximately 1,220 kilometers in radius and reaches temperatures of about 5,200 °C. The pressure within the core is nearly 3.6 million atmospheres.
The temperature of the inner core is significantly higher than the iron’s melting point. However, unlike the outer core, the inner core is not in a liquid or molten state. The intense pressure exerted on the inner core by the rest of the planet and its atmosphere prevents the iron from melting. The pressure and density are too immense for the iron atoms to transition into a liquid form. Due to these unique circumstances, some geophysicists prefer to view the inner core not as a solid, but as a plasma that exhibits solid-like behavior.
The liquid outer core acts as a barrier between the inner core and the rest of the Earth, resulting in the inner core rotating slightly differently from the rest of the planet. It rotates eastward, similar to the surface, but at a slightly faster pace, completing one extra rotation approximately every 1,000 years.
The crystal structure’s orientation results in seismic waves propagating faster in the north-south direction than in the east-west direction, making them the most reliable method for studying the core. Seismic waves take four seconds longer to travel from pole to pole than across the equator.
Expansion of the inner core
As the Earth gradually cools, the inner core expands by approximately one millimeter per year. This expansion occurs as the particles in the liquid outer core solidify or crystallize, a process also known as “freezing,” although it should be noted that the freezing point of iron is above 1000 °C.
The expansion of the inner core is not uniform and can be influenced by activity in the mantle.
Growth is primarily concentrated in regions known as subduction zones, where tectonic plates sink beneath the Earth’s lithosphere and into the mantle. These zones, located thousands of kilometers above the core, play a crucial role in the cooling process of the surrounding area as the subducted slabs draw heat away from the core and solidify.
In contrast, growth is less concentrated in areas called “superplumes” or LLSVPs, which refer to streams of hot matter known as mantle jets that flow from the lower layers of the mantle.
It is important to note that the core will not “freeze” completely. The process of crystallization is extremely slow, and the continuous radioactive decay within the Earth’s interior further slows it down. Scientists estimate that it will take approximately 91 billion years for the core to fully solidify, although the sun is expected to burn out much sooner, in about 5 billion years.
Significant hemispheres
The eastern and western hemispheres of the inner core exhibit different melting patterns and possess unique crystalline structures. Notably, the western hemisphere experiences a more rapid crystallization process compared to its eastern counterpart.
An Intriguing Discovery: The Core Within the Inner Core
In a recent breakthrough, geoscientists have unveiled the presence of a secondary core nested within the inner core, akin to a nucleus within a nucleus. This peculiar formation distinguishes itself from the inner core just as the latter distinguishes itself from the outer core. Researchers hypothesize that this internal core originated from a monumental geological event approximately 500 million years ago.
The orientation of the crystals in the nucleus, specifically in the inner core, is east-west instead of north-south. This particular alignment does not align with the Earth’s axis of rotation or the magnetic field. Scientists hypothesize that the iron crystals may possess an entirely different structure (non-HPU) or exist in a distinct form.
Approaches to investigating the Earth’s core
Directly examining the core is not possible for geophysicists. All knowledge regarding the core stems from intricate analysis of seismic data, examination of meteorites, laboratory experiments involving temperature and pressure, and computer simulations.
The majority of core research is conducted through the measurement of seismic waves, which are shock waves generated by earthquakes on or near the surface.
Seismic waves play a crucial role in helping geologists analyze the composition of the Earth’s core. During the late 19th century, scientists made an interesting observation regarding a “shadow zone” deep within the Earth. This zone was characterized by the disappearance or alteration of s-waves, which are unable to propagate through liquids or gases. The sudden absence of s-waves in this “shadow” region strongly suggested the presence of a liquid layer.
Advancements in the 20th century led geologists to discover that the speed of p-waves, another type of bulk wave, increased significantly at a depth of approximately 5150 kilometers. This increase in velocity indicated a transition from a liquid or molten medium to a solid medium. Consequently, the existence of a solid inner core was unequivocally confirmed.
Meteorites, celestial objects that descend to Earth, also provide valuable information about the Earth’s core. The majority of meteorites are fragments of asteroids, solid bodies that orbit the Sun in the region between Mars and Jupiter. These asteroids were formed at the same time and from the same materials as our planet. Through the analysis of chondrite meteorites that are rich in iron, geologists have gained insights into the early formation of our solar system as well as the composition of the Earth’s core during its early stages.
Within the laboratory setting, the most invaluable tool for studying the forces and reactions within the core is the “diamond anvil.” This device utilizes the hardest substance known to man, diamonds, to replicate the extraordinarily high pressures experienced in the core. By employing an X-ray laser to simulate the core’s temperature, the laser is directed through two diamonds, exerting pressure on a sample placed between them.
Central Part
Nucleus – The central part of the Earth’s sphere. It experiences extremely high pressure and temperature ranging from +4000 °C to +5000 °C. The nucleus is composed of the densest and heaviest substance, believed to be iron. It constitutes 30% of the Earth’s mass, but occupies only 15% of its volume.
The nucleus is situated at a depth exceeding 2900 km and has a radius of approximately 3550 km (inner nucleus – 1300 km, outer nucleus – 2250 km).
The solid inner part of the nucleus appears to be buoyant in the outer liquid layer. This movement generates a magnetic field around the Earth. It shields life on our planet from harmful cosmic rays. The magnetic field is detected by the compass needle.
The Earth’s Mantle
The Earth’s mantle (derived from the Greek word for “covering, cloak”) is the largest internal layer of our planet. It makes up the majority (over 80%) and carries most of the mass (nearly 70%) of the Earth. The mantle has a thickness of approximately 2900 km.
The mantle is composed of solid material, although it is less dense than the core. As we go deeper into the mantle, the pressure and temperature increase (averaging at +2000 °C – +2500 °C).
Located at the upper part of the mantle is a zone called the asthenosphere, where the materials are partially molten and exhibit plasticity. The solid layers above it move through this zone. The mantle is primarily composed of oxygen, silicon, and magnesium.
Crust of the Earth
The Earth’s crust – The Earth’s crust is the outermost and thinnest layer of the Earth’s structure: its maximum thickness (8 – 40 km) is 90 times smaller than the Earth’s radius. The Earth’s crust represents less than 1% of the Earth’s total mass and approximately 5% of its overall volume.
Exploring the Inner Depths of the Earth
Geology is the scientific field that focuses on studying the internal structure, origin, and evolution of the Earth.
Tectonics is a specific branch of geology that examines the structure of the Earth’s crust and the changes it undergoes.
Compared to outer space, the internal structure of the Earth remains relatively unexplored. The immense size of our planet presents significant challenges when it comes to directly observing and obtaining rock samples from great depths. In contrast, we have a much better understanding of the composition of the Earth’s uppermost solid layer, the crust, which is where humans reside. The Earth’s crust is made up of various minerals and rocks.
Geologists endeavor to delve as deep into the Earth as possible in order to investigate the composition and structure of rocks. The technique of borehole drilling facilitates this endeavor. Drilling is primarily carried out for the purpose of extracting oil, natural gas, and water from beneath the surface, for engineering projects, and for mineral exploration and prospecting.
The initial initiative of drilling wells for scientific purposes was undertaken in the Soviet Union. In 1970, drilling commenced at the Kola ultra-deep well near the town of Zapolyarny in the Murmansk region. The objective was to drill a well that was 15 kilometers deep. However, in 1991, drilling was halted after reaching a maximum depth of 12,261 meters due to limitations of the equipment used. The Kola well remains the deepest in the world.
Subsurface exploration using the seismic method
Seismic waves, generated by earthquakes and artificial explosions, induce vibrations in rocks. These vibrations can be categorized into longitudinal waves, which cause particles to oscillate back and forth, and transverse waves, which cause particles to move in perpendicular directions.
Special instruments called seismographs are used to measure these vibrations. A seismograph is a device that records vibrations in the Earth’s rocks caused by earthquakes, explosions, vibrations, or other sources. Seismographs produce curved lines known as seismograms, which depict the vibrations of particles in the Earth. Seismograms are examined by experts known as seismologists.
The density of rocks impacts the speed of waves: dense rocks experience faster wave propagation, while less dense rocks experience slower wave propagation. Only longitudinal waves can propagate through liquid mediums. Through seismic research, it has been established that the Earth consists of three main layers: the Earth’s crust, mantle, and core.
Gems
The Earth’s crust is comprised of a variety of rocks and minerals. These can be found in our everyday lives, such as table salt, graphite, talc, pumice, and marble, among others. Rocks and minerals possess distinct compositions, appearances, and colors.
Minerals are solid natural formations that are constituents of the Earth’s rocks and possess specific chemical compositions and structures. Rocks, on the other hand, are typically composed of multiple minerals.
Figure 3: Minerals and rocks
There are different types of rocks and minerals based on their origins:
1. Magmatic.
2. Sedimentary.
– Clastic
– Chemical
– Organic
3. Metamorphic.
Magmatic rocks are rocks formed from the cooling and solidification of magma.
Magmatic rocks can be classified as intrusive or effusive. Intrusive rocks form deep within the Earth’s crust through the slow solidification of magma. Examples of intrusive rocks include granite, gabbro, and olivinite. On the other hand, effusive rocks are formed by the rapid solidification of magma that has been erupted as lava. Examples of effusive rocks include basalt, picrite, and pumice.
Sedimentary rocks are rocks that are formed through the accumulation of sediments on the Earth’s surface. There are two types of sedimentary rocks: organic and inorganic (clastic and chemical). Clastic sedimentary rocks are formed through the weathering and erosion of pre-existing rocks, typically by wind or water. Examples of clastic sedimentary rocks include gravel, sand, clay, and pebbles.
