A demolition expert surveys the building designated for destruction. With one swing of the wrecking ball, he must bring down the building without scattering the debris off the property. Such a precise operation requires the right size wrecking ball hitting at just the right speed. Hitting too high only removes the roof; too low and the ground absorbs all the wrecking force. The possibilities for a failed demolition far exceed the ways to succeed. After exacting calculations, the wrecking ball scores a direct hit, transforming the building into an easily cleaned-up pile of debris.
About 50 million years after the formation of the solar system, a similarly fine-tuned collision between Earth and a Mars-sized body occurred. However, instead of destroying Earth, the collision provided raw materials for the formation of Earth's moon. The collision ejected debris into orbit that eventually coalesced into the Moon. Recent high-resolution simulations of the impact event1 confirm the fine-tuning of the impact to insure the survival of Earth, formation of the Moon, and transformation of Earth's atmosphere.2
The simulations show that the debris ejected from Earth must have consisted primarily of solid or liquid material-not gas-or else the debris disk would have dissipated too quickly to coalesce into a Moon-sized satellite. A larger impactor would have generated more energy during the collision and, consequently, more vaporized, gaseous material in the debris disk. However, a smaller impactor would not enrich Earth with the necessary heavy elements to drive long-standing plate tectonics nor provide sufficient energy to completely eject Earth's life-suffocating primordial atmosphere into space. (This gas does not become part of the debris disk, but is completely removed from the Earth-Moon system.) Thus, if the impactor were larger or smaller, the capacity of Earth to support advanced complex life (like humans) or abundant, long-standing microbial life rapidly diminishes. Additionally, the authors note that if a planet is too large, it cannot have a moon formed by a giant impact event. The Moon-forming impact requires a just-right-sized impactor striking Earth at the just-right speed, at the just-right location, with the just-right angle, and at the just-right time.
Just as the demolition expert must carefully prepare his work in order to avoid failure, so the Moon-forming impact required a number of just-right factors in order to succeed. As scientific advances continue to reveal more fine-tuning factors, the idea that the impact happened purely by chance seems less and less feasible. On the other hand, such fine-tuning comports well with RTB's biblical creation model, in which a supernatural Creator intervenes to ensure Earth's long-standing habitability in preparation for humankind.