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Nuclear fusion is the process by which two or more atomic nuclei join
together, or "fuse", to form a single heavier nucleus. This is usually
accompanied by the release of large quantities of energy. Fusion is the process
that powers active stars, the hydrogen bomb and some experimental devices
examining fusion power for electrical generation.
The fusion of two nuclei with lower masses than iron (which, along with nickel,
has the largest binding energy per nucleon) generally releases energy, while
the fusion of nuclei heavier than iron absorbs energy. The opposite is true for
the reverse process, nuclear fission. This means that fusion generally occurs for
lighter elements only, and likewise, that fission normally occurs only for heavier
elements. There are extreme astrophysical events that can lead to short
periods of fusion with heavier nuclei. This is the process that gives rise to
nucleosynthesis, the creation of the heavy elements during events such as
supernovas.
Creating the required conditions for fusion on Earth is very difficult, to the
point that it has not been accomplished at any scale for protium, the common
light isotope of hydrogen that undergoes natural fusion in stars. In nuclear
weapons, some of the energy released by an atomic bomb (fission bomb) is
used for compressing and heating a fusion fuel containing heavier isotopes of
hydrogen, and also sometimes lithium, to the point of "ignition". At this point,
the energy released in the fusion reactions is enough to briefly maintain the
reaction. Fusion-based nuclear power experiments attempt to create similar
conditions using far lesser means, although to date these experiments have
failed to maintain conditions needed for ignition long enough for fusion to be a
viable commercial power source.
Building upon the nuclear transmutation experiments by Ernest Rutherford,
carried out several years earlier, the laboratory fusion of heavy hydrogen
isotopes was first accomplished by Mark Oliphant in 1932. During the
remainder of that decade the steps of the main cycle of nuclear fusion in stars
were worked out by Hans Bethe. Research into fusion for military purposes
began in the early 1940s as part of the Manhattan Project, but this was not
accomplished until 1951 (see the Greenhouse Item nuclear test), and nuclear
fusion on a large scale in an explosion was first carried out on November 1,
1952, in the Ivy Mike hydrogen bomb test.
Research into developing controlled thermonuclear fusion for civil purposes
also began in earnest in the 1950s, and it continues to this day. Two projects,
the National Ignition Facility and ITER are in the process of reaching breakeven
after 60 years of design improvements developed from previous
experiments[citation needed].

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A supernova (abbreviated SN, plural SNe after supernovae) is a stellar
explosion that is more energetic than a nova. It is pronounced
/suprnov/ with the plural supernovae /suprnovi/ or supernovas.
Supernovae are extremely luminous and cause a burst of radiation that often
briefly outshines an entire galaxy, before fading from view over several weeks
or months. During this short interval a supernova can radiate as much energy as
the Sun is expected to emit over its entire life span.…read more

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His work helped to establish the basis of
modern geology. His theories of geology and geologic time, also called deep
time, came to be included in theories which were called plutonism and
uniformitarianism.…read more

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Continental drift
Antonio Snider-Pellegrini's Illustration of the closed and opened Atlantic Ocean
(1858).
Continental drift is the movement of the Earth's continents relative to each
other.The hypothesis that continents 'drift' was first put forward by Abraham
Ortelius in 1596 and was fully developed by Alfred Wegener in 1912.…read more

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This
led Mantovani to propose an Expanding Earth theory which has since been
shown to be incorrect.[12][13][14]
Some sort of continental drift without expansion was proposed by Frank
Bursley Taylor, who suggested in 1908 (published in 1910) that the continents
were dragged towards the equator by increased lunar gravity during the
Cretaceous, thus forming the Himalayas and Alps on the southern faces.
Wegener said that of all those theories, Taylor's, although not fully developed,
had the most similarities to his own.…read more

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The complementary arrangement of the facing sides of South America and
Africa is obvious, but is a temporary coincidence. In millions of years, slab pull
and ridge-push, and other forces of tectonophysics will further separate and
rotate those two continents. It was this temporary feature which inspired
Wegener to study what he defined as continental drift, although he did not
live to see his hypothesis become generally accepted.…read more

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Geophysicist Jack Oliver is credited with providing seismologic evidence
supporting plate tectonics which encompassed and superseded continental
drift with "Seismology and the New Global Tectonics," published in 1968, using
data collected from seismologic stations, including those he set up in the South
Pacific.[21]
It is now known that there are two kinds of crust, continental crust and oceanic
crust. Continental crust is inherently lighter and of a different composition to
oceanic crust, but both kinds reside above a much deeper fluid mantle.…read more

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