In this animation, Earth and Theia are represented by the agglomerations of particles. Earth is spinning super-fast--its day is only 2.3 hours long. Theia, which has about half the mass of Mars, careens toward Earth at 44,740 MPH. It penetrates all the way to Earth's core and excavates a massive hole in our planet, throwing material out in the process. Theia is mostly vaporized, along with part of our planet, and the iron from its core merges with Earth's core.