I. History of the Earth

• Formation of the Solar System
  • The Sun and its planets were formed around 4.6 x 10⁹ (4.6 billion) years ago.
  • Ages of Earth rocks 3.8 x 10⁹ years, Moon rocks 4.2 x 10⁹ years, and meteorites 4.6 x 10⁹ years have been accurately dated from radioactive decay of certain elements.

    Original Radio- active Isotope	Half-life (Billions of Years)	Final Stable Isotope
    Potassium (40K)	1.3	Argon (40Ar)
    Rubidium (87Rb)	47.0	Strontium (87Sr)
    Uranium (235U)	0.7	Lead (207Pb)
    Uranium (238U)	4.5	Lead (206Pb)

    The Sun's current temperature and luminosity indicate a 4.5 - 5.0 x 10⁹ year old 1 solar mass star consistent with the age of the oldest rocks in the solar system.
  
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