World of Knowledge (Australia) - - History -

A gi­gan­tic cloud of gas and dust formed in our gal­axy 4.6 bil­lion years ago. Grav­i­ta­tional forces and rising tem­per­a­tures (10,000,000°C) made the nu­clei of hy­dro­gen atoms move so quickly that a nu­clear re­ac­tion oc­curred, cre­at­ing our sun. The star will con­tinue to heat up and ex­pand un­til, in a bil­lion years’ time, the av­er­age tem­per­a­ture on Earth will ex­ceed the crit­i­cal value of 30°C, killing off most higher forms of life. In five bil­lion years, the sun will be­come a red gi­ant, hav­ing ex­panded to over 100 times its cur­rent size. One bil­lion years later, it will die, cast off its ex­ter­nal lay­ers and cre­ate a plan­e­tary neb­ula. A hot, dense core of oxy­gen and car­bon one and a half times larger than Earth will re­main: a white dwarf.

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