User:BornAYasMain/Geophysics

Original Article Paragraph: Regions of the Earth [Geophysics]

Size and form of the Earth [edit source]

Main article: Figure of the Earth

The Earth is roughly spherical, but it bulges towards the Equator, so it is roughly in the shape of an ellipsoid (see Earth ellipsoid). This bulge is due to its rotation and is nearly consistent with an Earth in hydrostatic equilibrium. The detailed shape of the Earth, however, is also affected by the distribution of continents and ocean basins, and to some extent by the dynamics of the plates.

Sharif's Edited Version (rephrasing of previous information, new information added, and other citations included)

Flattened Ellipsoid Shape of Earth

Contrary to popular belief, the earth is not entirely spherical but instead generally exhibits a roughly irregular ellipsoid shape- which is a result of the centrifugal forces the planet generates due to its' constant motion. These forces cause the planets diameter to bulge towards the Equator and results in the irregular ellipsoid shape. Earth's shape is constantly changing, and different factors including glacial isostatic rebound (large ice sheets melting causing the Earth's crust to the rebound due to the release of the pressure), geological features such as mountains or ocean trenches, tectonic plate dynamics, and natural disasters can further distort the planet's shape.

Mt.Fuji, mountain located in central Honshu, Japan

Mountains form in locations where two or more continental plates collide against one another- such as Mount Fujiwhich resides on top of three tectonic plates, Amur Plate, Okhotsk Plate, and Philippine Plate. As the plates collide, due to the similarity in their physical properties (thickness and weight), the plates end up folding into one another and throughout long periods of time, the remaining rocks end up gaining size and eventually forming a mountain. The formation, and erosion of mountains plays a significant part in altering the geological features and landform throughout time.

Original Article Paragraph: History [Geophysics]

Beginnings of modern science[edit source]

One of the publications that marked the beginning of modern science was William Gilbert's De Magnete (1600), a report of a series of meticulous experiments in magnetism. Gilbert deduced that compasses point north because the Earth itself is magnetic.

In 1687 Isaac Newton published his Principia, which not only laid the foundations for classical mechanics and gravitation but also explained a variety of geophysical phenomena such as the tides and the precession of the equinox.

The first seismometer, an instrument capable of keeping a continuous record of seismic activity, was built by James Forbes in 1844.

Sharif's Edited Version (more information, citations added, rephrasing of sentences)

Beginnings of modern science [edit source]

Portrait of William Gilbert (1544-1603)

The 17th century had major milestones that marked the beginning of modern science. In 1600, William Gilbert release a publication titled De Magnete (1600) where he conducted series of experiments on both natural magnets (called 'loadstones') and artificially magnetized iron . His experiments lead to observations involving a small compass needle (versorium) which replicated magnetic behaviours when subjected to a spherical magnet, along with it experiencing 'magnetic dips' when it was pivoted on a horizontal axis . His findings led to the deduction that compasses point north due to the Earth itself being a giant magnet .

In 1687 Isaac Newton published his work titled Principia which was pivotal in the development of modern scientific fields such as astronomy and physics. In it, Newton both laid the foundations for classical mechanics and gravitation, as well as explained different geophysical phenomena such as the precession of the equinox (the orbit of whole star patterns along an ecliptic axis). Newton's theory of gravity had gained so much success, that it resulted in changing the main objective of physics in that era to unravel natures fundamental forces, and their characterizations in laws.

Original Article Paragraph: Methods [Geophysics]

Remote sensing [edit source]

Main article: Remote sensing

Exploration geophysics is applied geophysics that often uses remote sensing platforms such as; satellites, aircraft, ships, boats, rovers, drones, borehole sensing equipment, and seismic receivers. Most correction for data gathered using geophysical methods such as magnetic, gravimetry, electromagnetic, radiometric, radar, laser altimetry, barometry, and Lidar, on remote sensing platforms involves the correction of the geophysical data gathered from that remote sensing platform due to the effects of that platform on the geophysical data. For instance, aeromagnetic data (aircraft gathered magnetic data) gathered using conventional fixed-wing aircraft platforms must be corrected for electromagnetic eddy currents that are created as the aircraft moves through Earth's magnetic field. There are also corrections related to changes in measured potential field intensity as the Earth rotates, as the Earth orbits the Sun, and as the moon orbits the Earth.

Sharif's Edited Version (many grammatical mistakes fixed, rephrasing of previous text)

Artist's concept of one of the six satellites part of NASA's OGO program

Exploration geophysics is a branch of applied geophysics that involves the development and utilization of different seismic or electromagnetic methods which the aim of investigating different energy, mineral and water resources. This is done through the uses of various remote sensing platforms such as; satellites, aircraft, boats, drones, borehole sensing equipment and seismic receivers. These equipment are often used in conjunction with different geophysical methods such as magnetic, gravimetry, electromagnetic, radiometric, barometry methods in order to gather the data. The remote sensing platforms used in exploration geophysics are not perfect and need adjustments done on them in order to accurately account for the effects that the platform itself may have on the collected data. For example, when gathering aeromagnetic data (aircraft gathered magnetic data) using a conventional fixed-wing aircraft- the platform has to be adjusted to account for the electromagnetic currents that it may generate as it passes through Earth's magnetic field.

Original Article Paragraph: Electricity

Electromagnetic waves

Electromagnetic waves occur in the ionosphere and magnetosphere as well as in Earth's outer core. Dawn chorus is believed to be caused by high-energy electrons that get caught in the Van Allen radiation belt. Whistlers are produced by lightning strikes. Hiss may be generated by both. Electromagnetic waves may also be generated by earthquakes (see seismo-electromagnetics).

In the highly conductive liquid iron of the outer core, magnetic fields are generated by electric currents through electromagnetic induction. Alfvén waves are magnetohydrodynamic waves in the magnetosphere or the Earth's core. In the core, they probably have little observable effect on the Earth's magnetic field, but slower waves such as magnetic Rossby waves may be one source of geomagnetic secular variation.

Electromagnetic methods that are used for geophysical survey include transient electromagnetics, magnetotelluric, surface nuclear magnetic resonance and electromagnetic seabed logging.

Sharif's Edited Version

In the world there are different charged particles, and when these charged particles come together and start vibrating, they can create either electric fields, or magnetic fields. These two types of vector fields when interacting with one another can come together to form electromagnetic waves, which is the phenomenon in which energy is transferred throughout the universe. James Clerk Maxwell, a Scottish physicist in the 19th century was known for developing the concept of electromagnetic radiation and subsequently the electromagnetic theory which stated that the formation of electric fields due to oscillating particles directly influences the formation of changing magnetic fields- and its the two continuously propagating vector fields that produce electromagnetic waves.

The electromagnetic wavelength spectrum

Electromagnetic waves come seven different types with different ranging frequencies/wavelength on the electromagnetic spectrum: radio waves, microwaves, infrared radiation (IR), X-rays, visible light, ultraviolet radiation (UV), and gamma rays. Radio waves are communicative waves that travel in the air and reflect off of satellites. Microwaves are a type of wavelength that is used for different applicatory purposes such as in cellphones, or for radar and heating purposes. Infrared radiation waves on the electromagnetic spectrum are invisible to the human eye, yet can be detected through the sensation of heat. X-ray waves are similar to radio and microwaves, yet due to the highly energetic photons that make up it, can carry high levels of energy capable of damaging living cells. Visible light waves are wavelengths on the electromagnetic spectrum that the human eye can see and differentiate as color due to speciliazed cells in the human eye. Ultraviolet radiation are invisible waves that can be classified in 3 categories- UV-A, UV-B and UV-C and are mainly sourced from the sun, or artificial sources like tanning equipment. Gamma rays, on the electromagnetic spectrum have the shortest wavelength, yet carry the most energy. They are formed as a result of extremely hot objects like stars, or processes such as nuclear or supernova explosions. In order of largest to smallest wavelength, the seven types are ordered as: radio waves, microwaves, infrared radiation, visible light, ultraviolet radiation, and gamma rays .

In the planet, these wavelengths can propagate in the ionosphere and the magnetosphere and can lead to certain phenomenon occurring throughout the universe such as the Dawn Chorus. This phenomenon is a 'bird-like' chirping sound that frequently plays around time of day of dawn and can only be heard with the assistance of radio receivers. It is believed to be caused by high-energy electrons that get caught in the Van Allen radiation belt. Addition electromagnetic waves that propagate in the atmosphere include Whistler or Hiss waves. Whistler waves exhibit high to low frequency sounds and only last for intervals of a few seconds. They are typically generated as waves once a lightning strike discharges. Hiss waves on the other hand are located in the magnetosphere and are attributed to the evolution to the planets Van Allen radiation belt, along with its rings. Additionally, this type of electromagnetic wave is responsible for removing electrons from the Van Allen radiation belt and transferring them into the planet's upper atmosphere which is beneficial as the electrons can interfere with satellite's and other telecommunication devices .

Illustration of the convection current mechanism that generates the Earth's magnetic field by: Andrew Z. Colvin

Throughout the Earth's outer core, which consists of highly conductive liquid iron, the magnetic fields are generated as a result of the convection cycle of radioactive heating, and chemical differentiation. This convection cycle converts kinetic energy into both electrical and magnetic energy and it is those electrical currents flowing throughout the liquid iron, that result in the formation of the magnetic fields. Due to the conductivity of the Earth's outer core, Alfvén waves, which are magnetohydrodynamic waves that can be formed in the presence of any electrically conducting fluid that is surrounded by a magnetic field- can be found there. However due to being in the planet's core, they do not have a significant effect on the Earth's magnetic field as a whole. Other slower moving waves such as Rossby waves may have a more sizeable effect on the planet's magnetic field in the context of geomagnetic secular variation. This type of electromagnetic wave is common in the Earth's ocean and atmosphere, and is generated as a result of the planet's natural rotation.