The End of The World

For years man has explored the universe looking for lost galaxies and watching the planets and constellations that we knew existed. Also, throughout the centuries and in recent years, meteorites from beyond our solar system have made their way toward our planet, entered our atmosphere and impacted the earth. Scientists are continually on the lookout for such objects heading our way although most either veer past the earth, or when they do reach the earth, cause little notice and minor damage from their impact. What would happen if the Super Asteroid actually impacted the earth and destroyed life as we know it or pushed man back to the Stone Age?