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• The most popular theory of our universe's origin centers on a cosmic cataclysm unmatched in all of history—the Big Bang
• Before the big bang, scientists believe, the entire vastness of the observable universe, including all of its matter and radiation, was compressed into a hot, dense mass just a few millimeters across
• Big bang proponents suggest that some 10 billion to 20 billion years ago, a massive blast allowed all the universe's known matter and energy—even space and time themselves—to spring from some ancient and unknown type of energy
• The expansion has apparently continued, but much more slowly, over the ensuing billions of years
• Big Bang Theory

  Theory that the universe began from a single primordial atom
• Big Bang Theory

  • It received significant boosts by Edwin Hubble's observations that galaxies are speeding away from us in all directions
  • It received significant boosts from the discovery of cosmic microwave radiation by Arno Penzias and Robert Wilson
• The glow of cosmic microwave background radiation, which is found throughout the universe, is thought to be a tangible remnant of leftover light from the big bang

  
• The Big Bang Theory leaves several major questions unanswered, including the original cause of the Big Bang itself
• Astronomers have acquired the first direct evidence that gravitational waves rippled through our infant universe during an explosive period of growth called inflation
• NASA-developed detector technology on the BICEP2 telescope at the South Pole, in collaboration with the National Science Foundation, helped make this discovery

  
• Our universe burst into existence in an event known as the Big Bang 13.8 billion years ago
• Moments later, space itself ripped apart, expanding exponentially in an episode known as inflation
• The gravitational waves produced a characteristic swirly pattern in polarized light, called "B-mode" polarization
• The BICEP2 team used novel superconducting detectors to produce compelling evidence for the B-mode signal, providing the strongest support yet for cosmic inflation

  
• Before Nicolaus Copernicus described the modern heliocentric or sun-centered system of planetary motions in 1543, the Earth has been assigned the central place in the universe
• Theories about the origin of the solar system

  • Nebular Hypothesis
  • Planetesimal Theory
  • Dust Cloud Theory
  • Protoplanet Hypothesis

  
• Nebular Hypothesis

  • The solar system developed with the observed regularities in its motions
  • The planetary system was formed from materials removed from the sun by tidal action caused by a passing star

  
• Dust Cloud Theory

  • The nebula was assumed to have a composition mainly of hydrogen and helium, like the sun, with only 1% of heavier elements
  • The mass of this "Dust Cloud" was originally 10% of the sun's mass or about a hundred times as great as the present combined mass of the planets and satellites

  
• Protoplanet Hypothesis

  • The original nebula was so massive that on further contraction and flattening, it broke into separate clouds or protoplanets
  • These protoplanets remained stable in the tidal field of the sun and developed denser cores surrounded by large atmospheres of the lighter gases

  
• The Earth has several structures that give its shape and form, including the crust, mantle, and core
• Crust

  • The brittle outermost layer of the planet
  • It has a variable thickness ranging from five (5) to 10 km from ocean basins to 25 to 70 km from the continents
• Mantle

  • The dense layer of the Earth composed only of molten silicate rocks
  • It is always in perpetual convection motion due to the core heating
• Solar system

  Built upon several layers of materials left behind during the stellar formation of the sun
• Terrestrial planets

  • Mercury, Venus, Earth, and Mars
• Gas giants

  • Jupiter, Saturn, Uranus, and Neptune
• Earth's structure

  Crust, Mantle, Core
• Crust

  • Brittle outermost layer of the planet, variable thickness ranging from 5 to 10 km from ocean basins to 25 to 70 km from the continents
• Mantle

  • Dense layer of the Earth composed only of molten silicate rocks, in perpetual convection motion due to the core heating it, varies in physical characteristics with depth
• Core

  • Hottest layer of the Earth, source of the Earth's magnetic field, has a liquid outer core and a molten, solid inner core
• Parts of the Earth

  • Lithosphere
  • Hydrosphere
  • Biosphere
  • Atmosphere
• Lithosphere

  The rocky crust of the Earth, including the uppermost mantle and the crust
• Hydrosphere

  All the waters that circulate on Earth, including oceans, seas, rivers, lakes, and moisture in the air
• Atmosphere

  The mass of air surrounding the planet, subdivided into different layers of different densities, composed primarily of nitrogen and oxygen
• Biosphere

  All living organisms, from the smallest bacteria to the largest whale, including plants, animals, and single-celled organisms
• The biosphere includes the uppermost geosphere, the hydrosphere, and the lower parts of the atmosphere
• Sea life concentrates near the surface, where sunlight is available. Plants also grow on Earth's surface, with roots penetrating a few meters underground. Large populations of bacteria live in rocks to depths of as much as 4 kilometers, some organisms live on the ocean floor, and a few windblown microorganisms drift at heights of 10 kilometers or more
• The biosphere is a very thin layer at Earth's surface
• Plants and animals are affected by the Earth's environment, and they also alter and form the environment they live in
• Characteristics of Earth necessary to support life

  Water, Energy, Time, Recycling
• Water

  An excellent solvent, capable of dissolving many substances, and floats when frozen, allowing underlying fluid to remain liquid