The aim of this lecture is to present on threats to Earth. Here briefly describe about the properties of asteroids and how asteroids have affected Earth in the past. This lecture also explain why the asteroid belt is between Mars and Jupiter: the large gravity of Jupiter disrupts the formation of a planet. Since earth formed over 4.5 billion years ago, Earth has been hit many times by asteroids and comets whose orbits bring them into the inner solar system. Finally focus on how can asteroids and comets be seen and what is the difference between a comet and an asteroid.