Subject:
All Disciplines Arts & Humanities Biology & Life Sciences Business & Economics Chemistry & Materials Science Computer Science & Mathematics Engineering Environmental & Earth Sciences Medicine & Pharmacology Physical Sciences Public Health & Healthcare Social Sciences
Sort:
Hottest Latest Alphabetical (A-Z) Alphabetical (Z-A)
Type:
All Topic Review Biography
Topic Review
Pole Shift Hypothesis
The cataclysmic pole shift fringe theory suggests that there have been geologically rapid shifts in the relative positions of the modern-day geographic locations of the poles and the axis of rotation of the Earth, creating calamities such as floods and tectonic events. There is evidence of precession and changes in axial tilt, but this change is on much longer time-scales and does not involve relative motion of the spin axis with respect to the planet. However, in what is known as true polar wander, the solid Earth can rotate with respect to a fixed spin axis. Research shows that during the last 200 million years a total true polar wander of some 30° has occurred, but that no super-rapid shifts in the Earth's pole were found during this period. A characteristic rate of true polar wander is 1° or less per million years. Between approximately 790 and 810 million years ago, when the supercontinent Rodinia existed, two geologically rapid phases of true polar wander may have occurred. In each of these, the magnetic poles of the Earth shifted by approximately 55°.
  • 8.8K
  • 10 Oct 2022
Topic Review
Polar Vortex Causes Temporal Variability of Solar-Atmospheric Links
The stratospheric polar vortex is a large-scale cyclonic circulation that forms in a cold air mass in the polar region and extends from the middle troposphere to the stratosphere. The polar vortex is implicated in a variety of atmospheric processes, such as the formation of ozone holes, the North Atlantic and the Arctic Oscillations, variations in extratropical cyclone tracks, etc. The vortex plays an important part in the mechanism of solar activity influence on lower atmosphere circulation, with variations in the vortex intensity being responsible for temporal variability in the correlation links observed between atmospheric characteristics and solar activity phenomena. In turn, the location of the vortex is favorable for the influence of ionization changes associated with charged particle fluxes (cosmic rays, auroral and radiation belt electrons) that affect the chemical composition and temperature regime of the polar atmosphere as well as its electric properties and cloudiness state. 
  • 382
  • 08 Aug 2022
Topic Review
Polar Forests of the Cretaceous
Cretaceous polar forests were temperate forests that grew at polar latitudes during the final period of the Mesozoic Era, known as the Cretaceous Period 145–66 Ma. During this period, global average temperature was about 10 °C (18 °F) higher and carbon dioxide (CO2) levels were approximately 1000 parts per million (ppm), 2.5 times the current concentration in Earth's atmosphere. The abundance of atmospheric carbon dioxide had a very significant impact on global climate and Earth's natural systems as its concentration is considered one of the main factors in the development of a pronounced greenhouse Earth during the Cretaceous with a very low average global temperature gradient. As a consequence, high paleolatitudes in both hemispheres were much warmer than at present. This temperature gradient was partly responsible for the lack of continental ice sheets in polar regions. As a response to elevated global temperatures, the Earth's hydrologic cycle was significantly enhanced due to greater volume of moisture evaporation from the surface of the ocean. In turn, the absolute sea level during this time period stood at elevations much higher than the present level. Continental encroachment of seawater formed widespread shallow seas, including expanses of epeiric seas. An increase in surface area between shallow, warm epeiric seawater and the atmosphere permits higher evaporation rates and more precipitation at various latitudes, producing a more temperate global climate. A widespread temperate climate also had significant effects on high latitude ecosystems.
  • 595
  • 02 Nov 2022
Topic Review
Point-Based Groundwater Monitoring
The initial type of groundwater investigation started with level measurements with different types of instruments, which is called point-based groundwater monitoring. These methods and instruments include steel tape, electronic measuring tapes, pressure transducers, sounding devices, test drilling, geophysical investigation techniques, piezometers, digital water level recorders, exploratory well drilling, and isotopes, etc.
  • 780
  • 15 Feb 2022
Topic Review
PM0.1 in Southeast Asian Cities
PM0.1 (particles with a diameter ≤ 0.1 µm), nanoparticles (NPs), or ultrafine particles (UFPs) were interchangeably used in the scientific communities. PM0.1 originated from both natural and human sources.
  • 706
  • 30 Aug 2022
Topic Review
Pliosaurus
Pliosaurus (meaning 'more lizard') is an extinct genus of thalassophonean pliosaurid known from the Kimmeridgian and Tithonian stages (Late Jurassic) of Europe and South America. Their diet would have included fish, cephalopods, and marine reptiles. This genus has contained many species in the past but recent reviews found only six (P. brachydeirus, P. carpenteri, P. funkei, P. kevani, P. rossicus and P. westburyensis) to be valid, while the validity of two additional species awaits a petition to the International Code of Zoological Nomenclature. Currently, P. brachyspondylus and P. macromerus are considered dubious, while P. portentificus is considered undiagnostic. Most species of Pliosaurus reached 8 metres (26 ft) in length and 5 metric tons (5.5 short tons) in body mass, while P. rossicus and P. funkei may have reached or even exceeded 10 metres (33 ft) in length and 11 metric tons (12 short tons) in body mass, being the largest plesiosaurs of all time. Species of this genus are differentiated from other pliosaurids based on seven autapomorphies, including teeth that are triangular in cross section.
  • 721
  • 16 Nov 2022
Topic Review
Platinum Group Minerals
Russia and South Africa are the world’s leading producers of platinum group elements (PGEs). This places them in a unique position regarding the supply of these two key industrial commodities. The purpose of this paper is to provide a comparative high-level overview of aspects of the geological occurrence, mineralogy, and processing by flotation of the platinum group minerals (PGMs) found in each country. A summary of some of the major challenges faced in each country in terms of the concentration of the ores by flotation is presented alongside the opportunities that exist to increase the production of the respective metals. These include the more efficient recovery of minerals such as arsenides and tellurides, the management of siliceous gangue and chromite in the processing of these ores, and, especially in Russia, the development of novel processing routes to recover PGEs from relatively low grade ores occurring in dunites, black shale ores and in vanadium-iron-titanium-sulphide oxide formations.
  • 2.1K
  • 26 Jan 2021
Topic Review
Platinum Group Elements Geochemistry and Mineralogy
Platinum (Pt), palladium (Pd), rhodium (Rh), iridium (Ir), ruthenium (Ru) and osmium (Os) are known as the platinum group elements (PGE). These metals are characterized by peculiar physical and chemical properties, such as high melting points, resistance to oxidation and corrosion, strong conductivity and ductility. 
  • 1.3K
  • 21 Dec 2022
Topic Review
Plastics in Agricultural Soils
Plastics, especially microplastics, are a diverse group of polymer-based particles, currently emerging as a global environmental threat—plastic pollution. 
  • 252
  • 18 Oct 2023
Topic Review Video
Plastic Waste Governance in Bangladesh
Plastic, an offer of modernity, is presenting a massive threat in altered forms, to our health and environment. Plastic does not only pollute the surface environment, fresh water, and marine ecosystems, but toxic elements released from plastics also percolate down the surface and contaminate groundwater, which we often use as ‘safe’ drinking water. This probable future risk is deeply rooted in the entire governance infrastructure of plastic waste which could potentially lead to contamination of groundwater. A recent study finds 81% of tap water samples collected worldwide contained plastic pollutants, which means that annually we may be ingesting between 3000 and 4000 microparticles of plastic from tap water.
  • 3.1K
  • 04 Mar 2022
  • Page
  • of
  • 270
Featured Entry Collections
>>

Featured Books

>>
Encyclopedia of Social Sciences
Encyclopedia of COVID-19
Encyclopedia of Fungi
Encyclopedia of Digital Society, Industry 5.0 and Smart City
Video Production Service
Feedback