Natural Environment

The natural environment, encompasses all living and non-living things occurring naturally on Earth or some region thereof. It is an environment that encompasses the interaction of all living species. The concept of the natural environment can be distinguished by components:

    * Complete ecological units that function as natural systems without massive human intervention, including all vegetation, microorganisms, soil, rocks, atmosphere and natural phenomena that occur within their boundaries.

    * Universal natural resources and physical phenomena that lack clear-cut boundaries, such as air, water, and climate, as well as energy, radiation, electric charge, and magnetism, not originating from human activity.

The natural environment is contrasted with the built environment, which comprises the areas and components that are strongly influenced by humans. A geographical area is regarded as a natural environment (with an indefinite article), if the human impact on it is kept under a certain limited level.

Composition

Earth science generally recognizes 4 spheres, the lithosphere, the hydrosphere, the atmosphere, and the biosphere as correspondent to rocks, water, air, and life. Some scientists include, as part of the spheres of the Earth, the cryosphere (corresponding to ice) as a distinct portion of the hydrosphere, as well as the pedosphere (corresponding to soil) as an active and intermixed sphere. Earth science (also known as geoscience, the geosciences or the Earth Sciences), is an all-embracing term for the sciences related to the planet Earth. There are four major disciplines in earth sciences, namely geography, geology, geophysics and geodesy. These major disciplines use physics, chemistry, biology, chronology and mathematics to build a qualitative and quantitative understanding of the principal areas or spheres of the Earth system.

 Geological activity

The Earth's crust, or lithosphere, is the outermost solid surface of the planet and is chemically and mechanically different from underlying mantle. It has been generated largely by igneous processes in which magma (molten rock) cools and solidifies to form solid rock. Beneath the lithosphere lies the mantle which is heated by the decay of radioactive elements. The mantle though solid is in a state of rheic convection. This convection process causes the lithospheric plates to move, albeit slowly. The resulting process is known as plate tectonics. Volcanoes result primarily from the melting of subducted crust material or of rising mantle at mid-ocean ridges and mantle plumes.

Paleontology

Paleontology (British: palaeontology) is the study of prehistoric life, including organisms' evolution and interactions with each other and their environments (their paleoecology). As a "historical science" it tries to explain causes rather than conduct experiments to observe effects. Paleontological observations have been documented as far back as the 5th century BC. The science became established in the 18th century as a result of Georges Cuvier's work on comparative anatomy, and developed rapidly in the 19th century. Fossils found in China since the 1990s have provided new information about the earliest evolution of animals, early fish, dinosaurs and the evolution of birds and mammals. Paleontology lies on the border between biology and geology, and shares with archaeology a border that is difficult to define. It now uses techniques drawn from a wide range of sciences, including biochemistry, mathematics and engineering. As knowledge has increased, paleontology has developed specialized subdivisions, some of which focus on different types of fossil organisms while others study ecological and environmental history, such as ancient climates.

Body fossils and trace fossils are the principal types of evidence about ancient life, and geochemical evidence has helped to decipher the evolution of life before there were organisms large enough to leave fossils. Estimating the dates of these remains is essential but difficult: sometimes adjacent rock layers allow radiometric dating, which provides absolute dates that are accurate to within 0.5%, but more often paleontologists have to rely on relative dating by solving the "jigsaw puzzles" of biostratigraphy. Classifying ancient organisms is also difficult, as many do not fit well into the Linnean taxonomy that is commonly used for classifying living organisms, and paleontologists more often use cladistics to draw up evolutionary "family trees". The final quarter of the 20th century saw the development of molecular phylogenetics, which investigates how closely organisms are related by measuring how similar the DNA is in their genomes. Molecular phylogenetics has also been used to estimate the dates when species diverged, but there is controversy about the reliability of the molecular clock on which such estimates depend.

Use of all these techniques has enabled paleontologists to discover much of the evolutionary history of life, almost all the way back to when Earth became capable of supporting life, about 3,800 million years ago. For about half of that time the only life was single-celled micro-organisms, mostly in microbial mats that formed ecosystems only a few millimeters thick. Earth's atmosphere originally contained virtually no oxygen, and its oxygenation began about 2,400 million years ago. This may have caused an accelerating increase in the diversity and complexity of life, and early multicellular plants and fungi have been found in rocks dated from 1,700 to 1,200 million years ago. The earliest multicellular animal fossils are much later, from about 580 million years ago, but animals diversified very rapidly and there is a lively debate about whether most of this happened in a relatively short Cambrian explosion or started earlier but has been hidden by lack of fossils. All of these organisms lived in water, but plants and invertebrates started colonizing land from about 490 million years ago and vertebrates followed them about 370 million years ago. The first dinosaurs appeared about 230 million years ago and birds evolved from one dinosaur group about 150 million years ago. During the time of the dinosaurs, mammals' ancestors survived only as small, mainly nocturnal insectivores, but after the non-avian dinosaurs became extinct in the Cretaceous–Tertiary extinction event 65 million years ago mammals diversified rapidly. Flowering plants appeared and rapidly diversified between 130 million years ago and 90 million years ago, possibly helped by coevolution with pollinating insects. Social insects appeared around the same time and, although they have relatively few species, now form over 50% of the total mass of all insects. The upright-walking common ancestor of humans and chimpanzees Sahelanthropus tchadensis appeared around 6 to 7 million years ago, and anatomically modern humans appeared under 200,000 years ago. The course of evolution has been changed several times by mass extinctions that wiped out previously dominant groups and allowed other to rise from obscurity to become major components of ecosystems.

Seismology

Seismology is the scientific study of earthquakes and the propagation of elastic waves through the Earth. The field also includes studies of earthquake effects, such as tsunamis as well as diverse seismic sources such as volcanic, tectonic, oceanic, atmospheric, and artificial processes (such as explosions). A related field that uses geology to infer information regarding past earthquakes is paleoseismology. A recording of earth motion as a function of time is called a seismogram.

Seismic waves

Earthquakes, and other sources, produce different types of seismic waves which travel through rock, and provide an effective way to image both sources and structures deep within the Earth. There are three basic types of seismic waves in solids: P-waves, S-waves (both body waves) and interface waves. The two basic kinds of surface waves (Rayleigh and Love) which travel along a solid-air interface, can be fundamentally explained in terms of interacting P- and/or S-waves.

Propagation of seismic wave in the ground and the effect of presence of land mine.


Pressure waves or Primary waves (P-waves), are longitudinal waves that travel at maximum velocity within solids and are therefore the first waves to appear on a seismogram.

S-waves, also called shear or secondary waves, are transverse waves that travel more slowly than P-waves and thus appear later than P-waves on a seismogram. Particle motion is perpendicular to the direction of wave propagation. Shear waves do not exist in fluids with essentially no shear strength, such as air or water.

Surface waves travel more slowly than P-waves and S-waves, but because they are guided by the surface of the Earth (and their energy is thus trapped near the Earth's surface) they can be much larger in amplitude than body waves, and can be the largest signals seen in earthquake seismograms. They are particularly strongly excited when the seismic source is close to the surface of the Earth, such as the case of a shallow earthquake or explosion.

For large enough earthquakes, one can observe the normal modes of the Earth. These modes are excited as discrete frequencies and can be observed for days after the generating event. The first observations were made in the 1960s as the advent of higher fidelity instruments coincided with two of the largest earthquakes of the 20th century - the 1960 Great Chilean earthquake and the 1964 Great Alaskan earthquake. Since then, the normal modes of the Earth have given us some of the strongest constraints on the deep structure of the Earth.

One of the earliest important discoveries (suggested by Richard Dixon Oldham in 1906 and definitively shown by Harold Jeffreys in 1926) was that the outer core of the Earth is liquid. Pressure waves (P-waves) pass through the core. Transverse or shear waves (S-waves) that shake side-to-side require rigid material so they do not pass through the outer core. Thus, the liquid core causes a "shadow" on the side of the planet opposite of the earthquake where no direct S-waves are observed. The reduction in P-wave velocity of the outer core also causes a substantial delay for P waves penetrating the core from the (seismically faster velocity) mantle.

Seismic waves produced by explosions or vibrating controlled sources are one of the primary methods of underground exploration in geophysics (in addition to many different electromagnetic methods such as induced polarization and magnetotellurics). Controlled source seismology has been used to map salt domes, faults, anticlines and other geologic traps in petroleum-bearing rocks, geological faults, rock types, and long-buried giant meteor craters. For example, the Chicxulub impactor, which is believed to have killed the dinosaurs, was localized to Central America by analyzing ejecta in the cretaceous boundary, and then physically proven to exist using seismic maps from oil exploration.

Using seismic tomography with earthquake waves, the interior of the Earth has been completely mapped to a resolution of several hundred kilometers. This process has enabled scientists to identify convection cells, mantle plumes and other large-scale features of the inner Earth.

Seismographs are instruments that sense and record the motion of the Earth. Networks of seismographs today continuously monitor the seismic environment of the planet, allowing for the monitoring and analysis of global earthquakes and tsunami warnings, as well as recording a variety of seismic signals arising from non-earthquake sources ranging from explosions (nuclear and chemical), to pressure variations on the ocean floor induced by ocean waves (the global microseism), to cryospheric events associated with large icebergs and glaciers. Above-ocean meteor strikes as large as ten kilotons of TNT, (equivalent to about 4.2 × 1013 J of effective explosive force) have been recorded by seismographs. A major motivation for the global instrumentation of the Earth with seismographs has been for the monitoring of nuclear testing.


One of the first attempts at the scientific study of earthquakes followed the 1755 Lisbon earthquake. Other especially notable earthquakes that spurred major developments in the science of seismology include the 1857 Basilicata earthquake, 1906 San Francisco earthquake, the 1964 Alaska earthquake and the 2004 Sumatra-Andaman earthquake. An extensive list of famous earthquakes can be found on the List of earthquakes page.
Earthquake prediction

Forecasting a probable timing, location, magnitude and other important features of a forthcoming seismic event is called earthquake prediction. Most seismologists do not believe that a system to provide timely warnings for individual earthquakes has yet been developed, and many believe that such a system would be unlikely to give significant warning of impending seismic events. More general forecasts, however, are routinely used to establish seismic hazard. Such forecasts estimate the probability of an earthquake of a particular size affecting a particular location within a particular time span and they are routinely used in earthquake engineering.

Various attempts have been made by seismologists and others to create effective systems for precise earthquake predictions, including the VAN method. Such methods have yet to be generally accepted in the seismology community.

Geoinformatics

Geoinformatics is the science and the technology which develops and uses information science infrastructure to address the problems of geography, geosciences and related branches of engineering.

Overview

Geoinformatics has been described as "the science and technology dealing with the structure and character of spatial information, its capture, its classification and qualification, its storage, processing, portrayal and dissemination, including the infrastructure necessary to secure optimal use of this information" or "the art, science or technology dealing with the acquisition, storage, processing production, presentation and dissemination of geoinformation" .

Geomatics is a similarly used term which encompasses geoinformatics, but geomatics focuses on surveying. Geoinformatics has at its core the technologies supporting the processes of acquiring, analyzing and visualizing spatial data. Both geomatics and geoinformatics include and rely heavily upon the theory and practical implications of geodesy.

Geography and earth science increasingly rely on digital spatial data acquired from remotely sensed images analyzed by geographical information systems (GIS) and visualized on paper or the computer screen .

Geoinformatics combines geospatial analysis and modeling, development of geospatial databases, information systems design, human-computer interaction and both wired and wireless networking technologies. Geoinformatics uses geocomputation and geovisualization for analyzing geoinformation.

Branches of geoinformatics include:

Cartography	Geodesy	Geographic Information Systems	Global Navigation Satellite Systems
Photogrammetry	Remote sensing	Web mapping

Applications

Many fields benefit from geoinformatics, including urban planning and land use management, in-car navigation systems, virtual globes, public health, local and national gazetteer management, environmental modeling and analysis, military, transport network planning and management, agriculture, meteorology and climate change, oceanography and coupled ocean and atmosphere modelling, business location planning, architecture and archeological reconstruction, telecommunications, criminology and crime simulation, aviation and maritime transport.