Our Earth might have formed a lot earlier that astronomers previously believed, maybe as quickly as 10 million years after the birth of the Sun. In fact, all of the inner planets might have started forming as soon as 10,000 years after the Sun ignited 4.5 billion years ago. Within 10 million years, the Earth had reached 64 percent of its mass, and later collided with a Mars-sized object to provide additional mass and create the Moon. Scientists originally believed that the Earth took 50 million years to form.