During the early days of the solar system, dozens of planets orbited the sun. It is thought that these planets collided and with this collision came intense heat which melted and welded rocks and minerals together. It is theorized that Mercury was only hit once hence it’s small size, Mars not at all, Venus 8x, and Earth 10x primarily because Earth it is the largest of the rocky planets. The last impact towards Earth is thought to have occurred 4,500,000,000 (4.5 billion) years ago which gave Earth its iron core; the lighter debris floated back above Earth and rotated around it which gave Earth rings similar to Saturn. Scientists now know that Earth was hit by rocks which came from Mars. It is thought that primitive microbial life would be able to withstand the journey from Mars to Earth. Earth had enough gravity to hold its oceans which allowed for constant changes in weather. It is thought that life began on Earth 4,300,000,000 (4.3 billion) years ago and that life became sophisticated 2,800,000,000 (2.8 billion) years ago. Despite the Earth being hit 6x catastrophically which was once thought to have sterilized all life, primitive life forms lay dormant in suspended animation within the salt rock which was produced from the immense heat during each catastrophic event. The microbes lay waiting until conditions became more favorable at which time they started reproducing and thriving. Scientists tested this first hand by drilling into salt rock which was created during a catastrophic event to release 200,000,000 (200 million) year old sea water which held tiny microbes called asilospermians which were reanimated when left within a nutrient rich solution for 4 months