One of the most fascinating things about the evolution of life on Earth is its connection to the sky above. Only under the most precise conditions cou
One of the most fascinating things about the evolution of life on Earth is its connection to the sky above. Only under the most precise conditions could tiny molecules have burst forth into life, and those conditions would not have been the same if our solar system lacked its current configuration. If there were only small differences in the orbits or locations of our Moon, the Sun or the surrounding planets, Earth might today be a cold, dead planet, and none of us would ever have existed.
The Sun is of course the most influential presence in our solar system. Without its immense and nearly timeless capacity to pour out enormous quantities of heat and light, the section of space we occupy would have been perpetually trapped in temperatures approaching absolute zero.
But the Moon plays a tremendously important role in mediating conditions on Earth as well. The Moon is not simply a spectator dragged along by our gravitational pull, but an active participant in Earth’s geological and biological development. Just as parents and children help shape each other, so, too, do the Moon and the Earth act as co-creators of the interconnected Earth-Moon system.
Without the Moon, occupying its current position and orbit, life may never have appeared on the Earth billions of years ago.
The Moon and Evolution
In 1993, Jacques Laskar, the director of the French National Center for Scientific Research, performed a careful analysis of the Moon’s effect on the tilt of the Earth’s axis . At present the Earth is tilted at an angle of 23.5 degrees either toward or away from the Sun, depending on where the planet is located during its 365-day revolution around the solar plane. Laskar determined that without a large satellite, our tilt would become more unstable over time, which could radically change climate conditions on the planet. This would have made evolution problematic, or at least caused it to unfold differently.
We may occasionally curse this tilt, when winter arrives and temperatures plunge well below the freezing point. But putting up with a little discomfort for a few months each year is a small price to pay, when you realize that without the Moon’s impact life on Earth would either not exist or would possess an alternate set of characteristics.
If creatures had managed to evolve on a Moon-less Earth—which is no sure thing—for the most part their daily lives would have been severely difficult and fraught with uncertainty. Even if such creatures existed, conditions might have made it impossible for them to evolve beyond simple, non-complex forms. This is uncertain, but it is a possibility.
If the Earth’s axis would vary by several degrees, extreme weather would plague the Earth and life would struggle to adapt and survive. As it is, the tilt of the Earth’s axis does change, over a period of tens of thousands of years. But the historical record shows this tilt has only varied between 22.1 percent and 24.5 percent, which can trigger climate changes but does not put life on Earth at risk.
This relative stability is related to the presence of our Moon. Without a Moon, our axis would swing more quickly and more dramatically. Recent calculations (in 2011) from a trip of scientists —Jack Lissauer of NASA’s Ames Research Center, Jason Barnes from the University of Idaho, and John Chambers of the Carnegie Institution for Science—proved the Earth’s tilt could vary by up to 10 degrees if the Moon were not in its current orbit exerting its stabilizing effect.
This is actually much less than the figures arrived at by Laskar, who predicted the Earth might flip on its side if the Moon were not present. The newer figures are considered more reliable, however, because of advancements in calculating power and computer technology.
But even with these more modest changes, it would likely be enough to cause the Earth to descend into severe Ice Ages on a more regular basis. Areas of the planet that were livable might become completely inhospitable within a century or two, as a result of the added instability. While intelligent life might have a chance to evolve on such a world, its efforts to build a sustainable civilization would likely be sabotaged by constant cycles of destruction and significant climate change. In such circumstances, a nomadic lifestyle would be the only alternative, virtually guaranteeing a spartan existence and a low population base.
In addition to keeping the tilt of our axis, the Moon gave evolution a boost in another way. Over four billion years ago, the Moon was much closer to Earth than it is now. Consequently, the tides extended several hundred miles inland. As a consequence, coastal areas saw massive cyclical changes in salinity that may have enabled the formation and evolution of self-replicating molecules, which eventually created life as we know it.
In general, the lack of strong tides that the Moon’s gravity precipitates would have had a dramatic impact on the course of evolution.
The Sun’s gravitational pull does contribute to the movements of the tides. But the Moon is responsible for two-thirds of the tidal effect, meaning that tides would be far more restrained in their cycles of movement if only the Sun were creating them.
The vigorous tides we currently experience help regulate ocean currents that distribute cold and heated water across the globe. Their mixing effect helps even out extremes and keeps the world’s climate more in balance between the latitudes.
A huge decrease in tidal forces would have meant larger differences in temperatures between north, south and center. If life had evolved, it would have likely been confined to areas relatively close to the equator—but without the Moon the tilt of the Earth’s axis would have been unstable, making the location of the equator relevant to the Sun variant and therefore not guaranteed of remaining warm for long.
Clearly, having the Moon is a blessing for which we should all give thanks.
Our Protector in the Skies
In 2013, the hit movie “ Oblivion” saw mankind dealing with the aftermath of the destruction of the Moon by nefarious robot aliens. Humanity, led by Tom Cruise, strove to overcome the effects of tsunamis, earthquakes, volcanoes, violent storms and other impacts caused by the loss of our satellite.
Should the Moon be wiped out by any type of catastrophe, or even somehow moved out of its present orbit, it would be a disaster of unmatched—and possibly un-survivable—proportions.
If alien invaders ever did arrive, with conquest on their minds, obliterating the Moon might be one of their first salvos in their war against us. Or, if they had the technology to do so, they might simply steer the Moon into a different orbit and let that change do all the work.
By moving it closer, they could dramatically increase the strength of the tides and quickly flood every coastal city and its surrounding area. Since 8 0 percent of human beings live within 100 kilometres of a coastline , this would virtually destroy civilization and heavily depopulate the planet within a few days time.
On the other hand, if the alien invaders were busy conquering other worlds and wanted to prepare Earth for an invasion a few thousand years in the future, they could take the opposite approach and move the Moon farther away. This would all but shut down the tides and eventually cause our planet to tilt off its axis to a disturbing degree, likely enough to cause an unimaginable catastrophe with a massive loss of life.
Invasion from space may or may not be a real risk. But regardless of any scenario we might imagine, it is indisputable that if the Moon were destroyed or otherwise ceased to exist, our prospects for survival would be grim.
Top image: Moon destruction. Credit: k_yu / Adobe Stock
By Nathan Falde