The Earth in SpaceEarth OriginEarth is the third planet from the Sun, one of eight "classical" planets recognized by the International Astronomical Union. Pluto, defined as a planet until recently was downgraded. It is thought that our Earth originated from the accretion of bits of solid matter left from the massive explosion of a star or supernova. Bits of material were scattered into space forming a slowly rotating cosmic gas cloud. Gravity slowly gathered the thinly spread atoms of the cosmic cloud. As the atoms moved closer together the gas became hotter and more dense. A new sun was born as hydrogen eventually became so tightly compressed and temperatures so high that nuclear burning began. A flattened rotating disc of gas and dust surrounded the young sun. Outer cooler parts of the disc or star nebulae began to condense to form the building blocks of future planets. It is believed that the Earth was
created by the accretion of cold particles and originally had a
homogeneous composition throughout. During the later part of the
accretion phase, the Earth was likely heated by kinetic energy of
objects colliding with the surface. Combined with the heat generated
from radioactive decay of isotopes in the developing earth, the high
temperature environment caused the entire planet to melt. Iron was
pulled inward toward the core by gravity as lighter minerals - silicon,
magnesium and aluminum - migrated upward, cooling to form the Earth's
crust about 4.6 billion years ago. Figure ES.2 Image of the spiral galaxy NGC 4414 (Source: NSSDC NASA) As the planet cooled, solar radiation stripped away its original gasses to be replaced by those trapped beneath the surface and later released by volcanic venting also known as outgassing. The volcanic vapors, like water vapor, vented into the evolving atmosphere and condensed to form clouds, and ice comets appear to have contributed water vapor to the atmosphere. However, the surface was still too hot for water to collect. That which fell to the surface as precipitation quickly vaporized and re-entered the atmosphere to condense once again. As the surface cooled, precipitation finally filled basins and depressions forming the first oceans. The Earth was now on its evolutionary way towards the planet we live on today. The tectonic forces creating the surface configuration of oceans and continents today will be taken up in other modules.
Figure ES.* Watch "Birth of the Solar System" Courtesy National Geographic |
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ES.1 The Solar System (