Well, it is not quite that simple. Just as the sun was being born, it sat in the middle of a pancake disk of gas and dust particles. These dust particles were constantly colliding and forming bigger and bigger objects. Eventually after 10 to 30 million years this process of collision and amalgamation created the PROTOPLANETS. These bodies kept colliding, and finally after about 70 million years formed the planets pretty much as we see them today. This process is called COLLISIONAL ACCRETION. Without it, we would not be here!

It was a lot more than just two asteroids. There were a lot of asteroids that ran into each-other and slowly built the Earth.

What a big question! The earth is around 4 billion years old (4 000 000 000), and for most of it's life there were no plants, animals or humans! That is because when the earth first formed, it didn't look at all like it does today. There were no continents like there are today, it was extremely hot and our atmosphere was mostly Carbon Dioxide back then, instead of oxygen! It took a few billion years before the atmosphere had more oxygen, and then different organisms started to form. Over thousands of years organisms developed until there were the plants and animals we see today.