(By Professor Neil F. Comins of the Department of Astronomy and Physics at the University of Maine in his research findings “What if the moon didn't exist?” — 1993 Harper Collins Publication)
The earth has a substantially large moon orbiting around it, which could not have possibly bulge off due to the earth's high rotational speed or have been captured by the earth's gravity, due to the moon's large mass.
The most likely explanation for the moon's existence would be a colossal accident in space, a collision of unimaginable magnitude where a Mars-sized planet crashed into the earth around 4.25 billion years ago (the age of the Moon). The probability of two planets colliding in the same solar system is extremely remote. Any "normal" collision would not have resulted in the formation of the moon, since the ejecta would not have been thrown far enough from the earth to form the moon. The small planet, before it collided with the earth, must have had an unusually elliptical orbit (unlike the orbit of any other planet in the Solar System), which resulted in a virtual head-on collision.
The collision of the small planet with the earth would have resulted in the ejection of 5 billion cubit miles of the earth's crust and mantle into orbit around the earth. This ring of material, the theory states, would have coalesced to form the moon. In addition, the moon is moving away from the earth (currently at 2 inches per year), as it has been since its creation. If we calculate backwards we discover that the moon must have formed just outside the Roche limit, the point at which an object would be torn apart by the earth's gravity (7,300 miles above the earth's surface). A collision which would have ejected material less than the Roche limit would have formed only rings around the earth. Computer models show that a collision of a small planet with the earth must have been very precise in order for any moon to have been formed at all.
The creation of the moon had a cataclysmal effect on the evolution of life on earth. The collision of the small planet with the earth also resulted in the ejection of the majority of the earth's primordial atmosphere. If this collision had not occurred, we would have had an atmosphere similar to that of Venus, which is 80 times that of the earth (equivalent to being one mile beneath the ocean). Such a thick atmosphere on Venus resulted in a runaway greenhouse affect, leaving a dry planet with a surface temperature of 800°F. The earth would have suffered a similar fate if the majority of its primordial atmosphere had not been ejected into outer space. In fact, the Earth is 20% more massive than Venus and further away from the Sun, both factors of which should have lead to a terrestrial atmosphere much thicker than that of Venus. For some strange reason, we have a very thin atmosphere - just the right density to maintain the presence of liquid, solid and gaseous water necessary to life.
Assuming our earth never had any moon, scientists would first train their eyes on the geo-physical aspects of earth in the new context. It is the tides pattern that would be most significant. There would be no gravitational pull by the moon and whatever tides the earth had would depend only on the pull by the sun. The tides would necessarily be very gentle and restricted within the same range. The tide behaviour would have other far-reaching effects. Powerful tides in our world hit the ocean floor and shorelines in great force and tend to apply a sort of brake on the speed of earths rotation.
During a span of 4.5 billion years the strong gravitational pull of the moon and its effect on tides had been able to lengthen our earthly days from 6 hours at the beginning to 24 hours by slowing down the speed of rotation. Likewise, the gravitational attraction of the earth on the moon has reduced its rotational period to 29 days. A moonless earth, the Professor calculates, would have 8-hour day and a year comprising 1,095 eight-hour days. Its rotation speed would be three times higher than at of our good earth.
Such a rapid rotational period would have resulted in surface wind velocities in excess of 200 miles per hour. Winds are generated by the planet's rotation and the heating and cooling of its air. The rotation drags air along the planet's surface. The faster rotation of the moonless earth would drag air along its equatorial surface much more forcefully than on our earth. There would be much less wind movement to north and south leading to an exceptional global climatic pattern. The fast rotation would cause wind whipping at tremendous speed over the torrid zone, regularly topping 200 miles per hour, while violent hurricanes would continuously hit the surface. A similar situation exists on the Jupiter and the Saturn each having 10-hour days where storms with wind speed around 300 mph rage the surface for years and even for centuries.
Another fortuitous result of the collision of the Mars-sized planet with the Earth is the presence of the Earth's large and heavy metallic core. In fact, the Earth has the highest density of any of the planets in our Solar System. This large nickel-iron core is responsible for our large magnetic field. This magnetic field produces the Van-Allen radiation shield, which protects the Earth from radiation bombardment. If this shield were not present, life would not be possible on the Earth. The only other rocky planet to have any magnetic field is Mercury. But its field strength is 100 times less than the Earth's. Even Venus, our sister planet, has no magnetic field. The Van-Allen radiation shield is a design unique to the Earth.