Earth

Question

This piglix contains articles or sub-piglix about Earth

Answer 1

Figure of the Earth

The expression figure of the Earth has various meanings in geodesy according to the way it is used and the precision with which the Earth's size and shape is to be defined. While the sphere is a close approximation of the true figure of the Earth and satisfactory for many purposes, geodesists have developed a number of models to represent a closer approximation to the shape of the Earth.

The actual topographic surface is most apparent with its variety of land forms and water areas. This is, in fact, the surface on which actual Earth measurements are made. However, it is not feasible for exact mathematical analysis, because the formulas which would be required to take the irregularities into account would necessitate a prohibitive amount of computation. The topographic surface is generally the concern of topographers and hydrographers.

The Pythagorean concept of a spherical Earth offers a simple surface that is mathematically easy to deal with. Many astronomical and navigational computations use it as a surface representing the Earth. While the sphere is a close approximation of the true figure of the Earth and satisfactory for many purposes, to the geodesists interested in the measurement of long distances on the scale of continents and oceans, a more exact figure is necessary. Closer approximations range from modelling the shape of the surface of the entire Earth as an oblate spheroid or an oblate ellipsoid, to the use of spherical harmonics or local approximations in terms of local reference ellipsoids.

The idea of a planar or flat surface for Earth, however, is still sufficient for surveys of small areas, as the local topography is far more significant than the curvature. Plane-table surveys are made for relatively small areas, and no account is taken of the curvature of the Earth. A survey of a city would likely be computed as though the Earth were a plane surface the size of the city. For such small areas, exact positions can be determined relative to each other without considering the size and shape of the entire Earth.

In the mid- to late 20th century, research across the geosciences contributed to drastic improvements in the accuracy of the figure of the Earth. The primary utility (and the motivation for funding, mainly from the military) of this improved accuracy was to provide geographical and gravitational data for the inertial guidance systems of ballistic missiles. This funding also drove the expansion of geoscientific disciplines, fostering the creation and growth of various geoscience departments at many universities.

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Answer 2

Flag of Earth

A flag of Earth is a flag used to represent Earth. Although no flag has received any "official recognition" by any governmental body, some individuals and organizations have promoted designs for a flag. The most widely recognized flags associated with Earth are the flag of the United Nations and the Earth Day flag. Listed below are some of the unofficial contenders for a Flag of Earth.

A flag designed by John McConnell in 1969 for the first Earth Day is a dark blue field charged with The Blue Marble, a famous NASA photo of the Earth as seen from outer space. The first edition of McConnell's flag used screen-printing and used different colors: ocean and land were white and the clouds were blue. McConnell presented his flag to the United Nations as a symbol for consideration.

Because of the political views of its creator and its having become a symbol of Earth Day, the flag is associated with environmental awareness, and the celebration of the global community. It was offered for sale originally in the Whole Earth Catalog, and is the only flag which was endorsed by McConnell.

The Blue Marble image was placed in the public domain, and the public nature of this image was the basis of a legal battle that resulted in the invalidation of a trademark and copyright that was originally issued to the Earth Day flag through its original promotional entity, World Equity, Inc. This does not invalidate the official history of McConnell's flag, only the official patent that was issued on it.

The One Flag in Space initiative is an offshoot of the Space Generation Congress (SGC), the Space Generation Advisory Council's yearly world meeting. It promotes usage of the Blue Marble flag for space exploration (it does not explicitly mention it being McConnell's design).

Adopted in 1946, the flag of the United Nations has been used to indicate world unity, although it technically only represents the United Nations itself. It has a geographical representation of the planet, and its high visibility usage makes it a well-known contender for representing Earth. During the planning for NASA's moon landings of the 1960s, it was suggested that a UN flag be used in place of the flag of the U.S.

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Answer 3

Future of Earth

The biological and geological future of Earth can be extrapolated based upon the estimated effects of several long-term influences. These include the chemistry at Earth's surface, the rate of cooling of the planet's interior, the gravitational interactions with other objects in the Solar System, and a steady increase in the Sun's luminosity. An uncertain factor in this extrapolation is the ongoing influence of technology introduced by humans, such as climate engineering, which could cause significant changes to the planet. The current Holocene extinction is being caused by technology and the effects may last for up to five million years. In turn, technology may result in the extinction of humanity, leaving the planet to gradually return to a slower evolutionary pace resulting solely from long-term natural processes.

Over time intervals of hundreds of millions of years, random celestial events pose a global risk to the biosphere, which can result in mass extinctions. These include impacts by comets or asteroids with diameters of 5–10 km (3.1–6.2 mi) or more, and the possibility of a massive stellar explosion, called a supernova, within a 100-light-year radius of the Sun, called a Near-Earth supernova. Other large-scale geological events are more predictable. If the long-term effects of global warming are disregarded, Milankovitch theory predicts that the planet will continue to undergo glacial periods at least until the Quaternary glaciation comes to an end. These periods are caused by eccentricity, axial tilt, and precession of the Earth's orbit. As part of the ongoing supercontinent cycle, plate tectonics will probably result in a supercontinent in 250–350 million years. Some time in the next 1.5–4.5 billion years, the axial tilt of the Earth may begin to undergo chaotic variations, with changes in the axial tilt of up to 90°.

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Answer 4

Gaia hypothesis

The Gaia hypothesis (/ˈɡaɪ.ə, ˈɡeɪ.ə/, GY-uh, GAY-uh), also known as the Gaia theory or the Gaia principle, proposes that organisms interact with their inorganic surroundings on Earth to form a synergistic self-regulating, complex system that helps to maintain and perpetuate the conditions for life on the planet. Topics of interest include how the biosphere and the evolution of life forms affect the stability of global temperature, ocean salinity, oxygen in the atmosphere, the maintenance of a hydrosphere of liquid water and other environmental variables that affect the habitability of Earth.

The hypothesis was formulated by the chemist James Lovelock and co-developed by the microbiologist Lynn Margulis in the 1970s. The hypothesis was initially criticized for being teleological and contradicting principles of natural selection, but later refinements resulted in ideas framed by the Gaia hypothesis being used in fields such as Earth system science, biogeochemistry, systems ecology, and the emerging subject of geophysiology. Even so, the Gaia hypothesis continues to attract criticism, and today some scientists consider it to be only weakly supported by, or at odds with, the available evidence. In 2006, the Geological Society of London awarded Lovelock the Wollaston Medal in part for his work on the Gaia hypothesis.

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Answer 5

Geographical distance

Geographical distance is the distance measured along the surface of the earth. The formulae in this article calculate distances between points which are defined by geographical coordinates in terms of latitude and longitude. This distance is an element in solving the second (inverse) geodetic problem.

Calculating the distance between geographical coordinates is based on some level of abstraction; it does not provide an exact distance, which is unattainable if one attempted to account for every irregularity in the surface of the earth. Common abstractions for the surface between two geographic points are:

All abstractions above ignore changes in elevation. Calculation of distances which account for changes in elevation relative to the idealized surface are not discussed in this article.

Distance, D,{\displaystyle D,\,\!} is calculated between two points, P1{\displaystyle P_{1}\,\!} and P2{\displaystyle P_{2}\,\!}. The geographical coordinates of the two points, as (latitude, longitude) pairs, are (Ï•<!-- ϕ -->1,λ<!-- λ -->1){\displaystyle (\phi _{1},\lambda _{1})\,\!} and (Ï•<!-- ϕ -->2,λ<!-- λ -->2),{\displaystyle (\phi _{2},\lambda _{2}),\,\!} respectively. Which of the two points is designated as P1{\displaystyle P_{1}\,\!} is not important for the calculation of distance.

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Answer 6

Geological history of Earth

The geological history of Earth follows the major events in Earth's past based on the geologic time scale, a system of chronological measurement based on the study of the planet's rock layers (stratigraphy). Earth formed about 4.54 billion years ago by accretion from the solar nebula, a disk-shaped mass of dust and gas left over from the formation of the Sun, which also created the rest of the Solar System.

Earth was initially molten due to extreme volcanism and frequent collisions with other bodies. Eventually, the outer layer of the planet cooled to form a solid crust when water began accumulating in the atmosphere. The Moon formed soon afterwards, possibly as a result of the impact of a planetoid with the Earth. Outgassing and volcanic activity produced the primordial atmosphere. Condensing water vapor, augmented by ice delivered from comets, produced the oceans.

As the surface continually reshaped itself over hundreds of millions of years, continents formed and broke apart. They migrated across the surface, occasionally combining to form a supercontinent. Roughly 750 million years ago, the earliest-known supercontinent Rodinia, began to break apart. The continents later recombined to form Pannotia, 600 to 540 million years ago, then finally Pangaea, which broke apart 200 million years ago.

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Answer 7

Geomagnetic reversal

A geomagnetic reversal is a change in a planet's magnetic field such that the positions of magnetic north and magnetic south are interchanged, while geographic north and geographic south remain the same. The Earth's field has alternated between periods of normal polarity, in which the direction of the field was the same as the present direction, and reverse polarity, in which the field was the opposite. These periods are called chrons.

The time spans of chrons are randomly distributed with most being between 0.1 and 1 million years with an average of 450,000 years. Most reversals are estimated to take between 1,000 and 10,000 years. The latest one, the Brunhes–Matuyama reversal, occurred 780,000 years ago, and may have happened very quickly, within a human lifetime.

A brief complete reversal, known as the Laschamp event, occurred only 41,000 years ago during the last glacial period. That reversal lasted only about 440 years with the actual change of polarity lasting around 250 years. During this change the strength of the magnetic field weakened to 5% of its present strength. Brief disruptions that do not result in reversal are called geomagnetic excursions.

In the early 20th century, geologists first noticed that some volcanic rocks were magnetized opposite to the direction of the local Earth's field. The first estimate of the timing of magnetic reversals was made by Motonori Matuyama in the 1920s; he observed that rocks with reversed fields were all of early age or older. At the time, the Earth's polarity was poorly understood, and the possibility of reversal aroused little interest.

Three decades later, when Earth's magnetic field was better understood, theories were advanced suggesting that the Earth's field might have reversed in the remote past. Most paleomagnetic research in the late 1950s included an examination of the wandering of the poles and continental drift. Although it was discovered that some rocks would reverse their magnetic field while cooling, it became apparent that most magnetized volcanic rocks preserved traces of the Earth's magnetic field at the time the rocks had cooled. In the absence of reliable methods for obtaining absolute ages for rocks, it was thought that reversals occurred approximately every million years.

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Answer 8

Geophysiology

Geophysiology (Geo, earth + physiology, the study of living bodies) is the study of interaction among living organisms on the Earth operating under the hypothesis that the Earth itself acts as a single living organism.

The term "geophysiology" was popularized by James Lovelock in his writings on the Gaia hypothesis. The term was in fact foreshadowed by many others. James Hutton (1726-1797), the "Father of Geology" in 1789, in a lecture presented on his behalf by Dr. Black, wrote "I consider the Earth to be a super-organism and that its proper study should be by physiology." This view that the Earth in some ways could be viewed as a superorganism was widely held in the early 19th century, and was supported even by such early biologists as Huxley (1825-1895), but is disputed today. An analogous alternative geophysiology which views the Earth as a single cell was developed by Lewis Thomas in his The Lives of a Cell: Notes of a Biology Watcher (1974).

Vladimir Vernadsky (1863-1945), founder of biogeochemistry suggested that geophysiological processes were responsible for the development of the Earth through a succession of phases in which the geosphere (of inanimate matter) develops into the biosphere (of biological life). Vernadsky's thinking significantly influenced the development of ecology in Russia, culminating in the "Russian Paradigm" (a term first coined by Georgii A. Zavarzin in 1995). The basic tenets of this approach are i) that life can only exist in the form of interconnected nutrient cycles (i.e. the ecosystem); ii) that ecosystem assembly is an organized process as opposed a haphazard one; iii) that the emergence of life on earth was congruent with respect to the appearance of primordial nutrient cycles; iv) that in addition to the evolution of species there exists a separate process of ecological evolution the direction of which is predetermined by community composition and dynamics (Lekevičius, 2006).

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Answer 9

Gravity of Earth

The gravity of Earth, which is denoted by g, refers to the acceleration that Is imparted to objects due to the distribution of mass within the Earth. In SI units this acceleration is measured in metres per second squared (in symbols, m/s² or m·s^−2) or equivalently in newtons per kilogram (N/kg or N·kg^−1). Near the Earth's surface, gravitational acceleration is approximately 9.8 m/s², which means that, ignoring the effects of air resistance, the speed of an object falling freely will increase by about 9.8 metres (32 ft) per second every second. This quantity is sometimes referred to informally as little g (in contrast, the gravitational constant G is referred to as big G).

The precise strength of Earth's gravity varies depending on location. The nominal "average" value at the Earth's surface, known as standard gravity is, by definition, 9.80665 m/s² (about 32.1740 ft/s²). This quantity is denoted variously as g_n, g_e (though this sometimes means the normal equatorial value on Earth, 9.78033 m/s²), g₀, gee, or simply g (which is also used for the variable local value). The weight of an object on the Earth's surface is the downwards force on that object, given by Newton's second law of motion, or F = ma (force = mass × acceleration). Gravitational acceleration contributes to the total acceleration, but other factors, such as the rotation of the Earth, also contribute, and, therefore, affect the weight of the object.

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Answer 10

History of Earth

The history of Earth concerns the development of the planet Earth from its formation to the present day. Nearly all branches of natural science have contributed to the understanding of the main events of the Earth's past. The age of Earth is approximately one-third of the age of the universe. An immense amount of geological change has occurred in that timespan, accompanied by the emergence of life and its subsequent evolution.

Earth formed around 4.54 billion years ago by accretion from the solar nebula. Volcanic outgassing probably created the primordial atmosphere and then the ocean; but the atmosphere contained almost no oxygen and so would have been toxic to most modern life including humans. Much of the Earth was molten because of frequent collisions with other bodies which led to extreme volcanism. A "giant impact" collision with a planet-sized body is thought to have been responsible for forming the Moon. Over time, the Earth cooled, causing the formation of a solid crust, and allowing liquid water to exist on the surface.

The geological time scale (GTS) clock (see graphic) depicts the larger spans of time from the beginning of the Earth as well as a chronology of some definitive events of Earth history. The Hadean Eon represents time before the reliable (fossil) record of life beginning on Earth; it began with the formation of the planet and ended at 4.0 billion years ago as defined by international convention. The Archean and Proterozoic eons follow; they produced the abiogenesis of life on Earth and then the evolution of early life. The succeeding eon is the Phanerozoic, which is represented by its three component eras: the Palaeozoic; the Mesozoic, which spanned the rise, reign, and climactic extinction of the huge dinosaurs; and the Cenozoic, which presented the subsequent development of dominant mammals on Earth.

Hominins, the earliest direct ancestors of the human clade, rose sometime during the latter part of the Miocene epoch; the precise time marking the first hominins is broadly debated over a current range of 13 to 4 mya. The succeeding Quaternary period is the time of recognizable humans, i.e., the genus Homo; but that period's two million-year-plus term of the recent times is too small to be visible at the scale of the GTS graphic. (Notes re the graphic: Ga means "billion years"; Ma, "million years".)

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