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.
Why Does the Moon Have Craters?
An asteroid or meteor is more likely to hit Earth because Earth is a lot bigger than the Moon, giving a meteoroid more area to hit! But we can see many thousands of craters on the Moon and we only know of about 180 on Earth! Why is that?
The truth is both the Earth and the Moon have been hit many, many times throughout their long 4.5 billion year history.
This view of the Moon's cratered South Pole was seen by NASA's Clementine spacecraft in 1996. Credit: NASA/JPL/USGS
What Would Happen to Earth if our Moon Were Obliterated? - History
I heard in the TV that moon is moving away from the earth towards the sun. Why is that happening? And when was this exactly discovered?
The Moon's orbit (its circular path around the Earth) is indeed getting larger, at a rate of about 3.8 centimeters per year. (The Moon's orbit has a radius of 384,000 km.) I wouldn't say that the Moon is getting closer to the Sun, specifically, though--it is getting farther from the Earth, so, when it's in the part of its orbit closest to the Sun, it's closer, but when it's in the part of its orbit farthest from the Sun, it's farther away.
The reason for the increase is that the Moon raises tides on the Earth. Because the side of the Earth that faces the Moon is closer, it feels a stronger pull of gravity than the center of the Earth. Similarly, the part of the Earth facing away from the Moon feels less gravity than the center of the Earth. This effect stretches the Earth a bit, making it a little bit oblong. We call the parts that stick out "tidal bulges." The actual solid body of the Earth is distorted a few centimeters, but the most noticable effect is the tides raised on the ocean.
Now, all mass exerts a gravitational force, and the tidal bulges on the Earth exert a gravitational pull on the Moon. Because the Earth rotates faster (once every 24 hours) than the Moon orbits (once every 27.3 days) the bulge tries to "speed up" the Moon, and pull it ahead in its orbit. The Moon is also pulling back on the tidal bulge of the Earth, slowing the Earth's rotation. Tidal friction, caused by the movement of the tidal bulge around the Earth, takes energy out of the Earth and puts it into the Moon's orbit, making the Moon's orbit bigger (but, a bit pardoxically, the Moon actually moves slower!).
The Earth's rotation is slowing down because of this. One hundred years from now, the day will be 2 milliseconds longer than it is now.
This same process took place billions of years ago--but the Moon was slowed down by the tides raised on it by the Earth. That's why the Moon always keeps the same face pointed toward the Earth. Because the Earth is so much larger than the Moon, this process, called tidal locking, took place very quickly, in a few tens of millions of years.
Many physicists considered the effects of tides on the Earth-Moon system. However, George Howard Darwin (Charles Darwin's son) was the first person to work out, in a mathematical way, how the Moon's orbit would evolve due to tidal friction, in the late 19th century. He is usually credited with the invention of the modern theory of tidal evolution.
So that's where the idea came from, but how was it first measured? The answer is quite complicated, but I've tried to give the best answer I can, based on a little research into the history of the question.
There are three ways for us to actually measure the effects of tidal friction.
* Measure the change in the length of the lunar month over time.
This can be accomplished by examining the thickness of tidal deposits preserved in rocks, called tidal rhythmites, which can be billions of years old, although measurements only exist for rhythmites that are 900 million years old. As far as I can find (I am not a geologist!) these measurements have only been done since the early 90's.
* Measure the change in the distance between the Earth and the Moon.
This is accomplished in modern times by bouncing lasers off reflectors left on the surface of the Moon by the Apollo astronauts. Less accurate measurements were obtained in the early 70's.
* Measure the change in the rotational period of the Earth over time.
Nowadays, the rotation of the Earth is measured using Very Long Baseline Interferometry, a technique using many radio telescopes a great distance apart. With VLBI, the positions of quasars (tiny, distant, radio-bright objects) can be measured very accuarately. Since the rotating Earth carries the antennas along, these measurements can tell us the rotation speed of the Earth very accurately.
However, the change in the Earth's rotational period was first measured using eclipses, of all things. Astronomers who studied the timing of eclipses over many centuries found that the Moon seemed to be accelerating in its orbit, but what was actually happening was that the Earth's rotation was slowing down. The effect was first noticed by Edmund Halley in 1695, and first measured by Richard Dunthorne in 1748--though neither one really understood what they were seeing. I think this is the earliest discovery of the effect.
This page was last updated on January 28, 2019.
About the Author
Britt studies the rings of Saturn. She got her PhD from Cornell in 2006 and is now a Professor at Beloit College in Wisconson.
We may not be entirely sure where we’d end up if we rewound time, but the paths available to evolving organisms are far from limitless
The winner essentially proved that the problem couldn’t be solved exactly. Much like the chaos introduced by random mutations, a little bit of starting error would inevitably grow, meaning that you couldn’t easily determine where the three bodies would end up in the future. But as the dominant partner, the sun dictates the orbits of all three to an extent – allowing us to narrow the possible positions of the bodies to within a range.
This is much like the guiding hands of evolution, which tether adapting organisms to familiar routes. We may not be entirely sure where we’d end up if we rewound time, but the paths available to evolving organisms are far from limitless. And so maybe humans would never appear again, but it’s likely that whatever alien world replaced ours, it would be a familiar place.
This article originally appeared on The Conversation, and is republished under a Creative Commons licence.
orbit: 384,400 km from Earth
diameter: 3476 km
mass: 7.35e22 kg
History of The Moon
Called Luna by the Romans, Selene and Artemis by the Greeks, and many other names in other mythologies.
The Moon, of course, has been known since prehistoric times. It is the second brightest object in the sky after the Sun. As the Moon orbits around the Earth once per month, the angle between the Earth, the Moon and the Sun changes we see this as the cycle of the Moon’s phases. The time between successive new moons is 29.5 days (709 hours), slightly different from the Moon’s orbital period (measured against the stars) since the Earth moves a significant distance in its orbit around the Sun in that time.
Due to its size and composition, the Moon is sometimes classified as a terrestrial “planet” along with Mercury, Venus, Earth and Mars.
The Moon was first visited by the Soviet spacecraft Luna 2 in 1959. It is the only extraterrestrial body to have been visited by humans. The first landing was on July 20, 1969 (do you remember where you were?) the last was in December 1972. The Moon is also the only body from which samples have been returned to Earth. In the summer of 1994, the Moon was very extensively mapped by the little spacecraft Clementine and again in 1999 by Lunar Prospector.
The gravitational forces between the Earth and the Moon cause some interesting effects. The most obvious is the tides. The Moon’s gravitational attraction is stronger on the side of the Earth nearest to the Moon and weaker on the opposite side. Since the Earth, and particularly the oceans, is not perfectly rigid it is stretched out along the line toward the Moon. From our perspective on the Earth’s surface we see two small bulges, one in the direction of the Moon and one directly opposite. The effect is much stronger in the ocean water than in the solid crust so the water bulges are higher. And because the Earth rotates much faster than the Moon moves in its orbit, the bulges move around the Earth about once a day giving two high tides per day. (This is a greatly simplified model actual tides, especially near the coasts, are much more complicated.)
But the Earth is not completely fluid, either. The Earth’s rotation carries the Earth’s bulges slightly ahead of the point directly beneath the Moon. This means that the force between the Earth and the Moon is not exactly along the line between their centers producing a torque on the Earth and an accelerating force on the Moon. This causes a net transfer of rotational energy from the Earth to the Moon, slowing down the Earth’s rotation by about 1.5 milliseconds/century and raising the Moon into a higher orbit by about 3.8 centimetres per year. (The opposite effect happens to satellites with unusual orbits such as Phobos and Triton).
The asymmetric nature of this gravitational interaction is also responsible for the fact that the Moon rotates synchronously, i.e. it is locked in phase with its orbit so that the same side is always facing toward the Earth. Just as the Earth’s rotation is now being slowed by the Moon’s influence so in the distant past the Moon’s rotation was slowed by the action of the Earth, but in that case the effect was much stronger. When the Moon’s rotation rate was slowed to match its orbital period (such that the bulge always faced toward the Earth) there was no longer an off-center torque on the Moon and a stable situation was achieved. The same thing has happened to most of the other satellites in the solar system. Eventually, the Earth’s rotation will be slowed to match the Moon’s period, too, as is the case with Pluto and Charon.
Actually, the Moon appears to wobble a bit (due to its slightly non-circular orbit) so that a few degrees of the far side can be seen from time to time, but the majority of the far side (left) was completely unknown until the Soviet spacecraft Luna 3 photographed it in 1959. (Note: there is no “dark side” of the Moon all parts of the Moon get sunlight half the time (except for a few deep craters near the poles). Some uses of the term “dark side” in the past may have referred to the far side as “dark” in the sense of “unknown” (eg “darkest Africa”) but even that meaning is no longer valid today!)
The Moon has no atmosphere. But evidence from Clementine suggested that there may be water ice in some deep craters near the Moon’s south pole which are permanently shaded. This has now been reinforced by data from Lunar Prospector. There is apparently ice at the north pole as well.
The Moon’s crust averages 68 km thick and varies from essentially 0 under Mare Crisium to 107 km north of the crater Korolev on the lunar far side. Below the crust is a mantle and probably a small core (roughly 340 km radius and 2% of the Moon’s mass). Unlike the Earth, however, the Moon’s interior is no longer active. Curiously, the Moon’s center of mass is offset from its geometric center by about 2 km in the direction toward the Earth. Also, the crust is thinner on the near side.
There are two primary types of terrain on the Moon: the heavily cratered and very old highlands and the relatively smooth and younger maria. The maria (which comprise about 16% of the Moon’s surface) are huge impact craters that were later flooded by molten lava. Most of the surface is covered with regolith, a mixture of fine dust and rocky debris produced by meteor impacts. For some unknown reason, the maria are concentrated on the near side.
Most of the craters on the near side are named for famous figures in the history of science such as Tycho, Copernicus, and Ptolemaeus. Features on the far side have more modern references such as Apollo, Gagarin and Korolev (with a distinctly Russian bias since the first images were obtained by Luna 3). In addition to the familiar features on the near side, the Moon also has the huge craters South Pole-Aitken on the far side which is 2250 km in diameter and 12 km deep making it the the largest impact basin in the solar system and Orientale on the western limb (as seen from Earth in the center of the image at left) which is a splendid example of a multi-ring crater.
A total of 382 kg of rock samples were returned to the Earth by the Apollo and Luna programs. These provide most of our detailed knowledge of the Moon. They are particularly valuable in that they can be dated. Even today, more than 30 years after the last Moon landing, scientists still study these precious samples.
Most rocks on the surface of the Moon seem to be between 4.6 and 3 billion years old. This is a fortuitous match with the oldest terrestrial rocks which are rarely more than 3 billion years old. Thus the Moon provides evidence about the early history of the Solar System not available on the Earth.
Prior to the study of the Apollo samples, there was no consensus about the origin of the Moon. There were three principal theories: co-accretion which asserted that the Moon and the Earth formed at the same time from the Solar Nebula fission which asserted that the Moon split off of the Earth and capture which held that the Moon formed elsewhere and was subsequently captured by the Earth. None of these work very well. But the new and detailed information from the Moon rocks led to the impact theory: that the Earth collided with a very large object (as big as Mars or more) and that the Moon formed from the ejected material. There are still details to be worked out, but the impact theory is now widely accepted.
The Moon has no global magnetic field. But some of its surface rocks exhibit remanent magnetism indicating that there may have been a global magnetic field early in the Moon’s history.
With no atmosphere and no magnetic field, the Moon’s surface is exposed directly to the solar wind. Over its 4 billion year lifetime many ions from the solar wind have become embedded in the Moon’s regolith. Thus samples of regolith returned by the Apollo missions proved valuable in studies of the solar wind.
The 54 surah of the Quran, entitled "The Moon" (Al-Qamar) begins:
اقْتَرَبَتِ السَّاعَةُ وَانشَقَّ الْقَمَرُ وَإِن يَرَوْا آيَةً يُعْرِضُوا وَيَقُولُوا سِحْرٌ مُّسْتَمِرٌّ
The Hour (of Judgment) is nigh, and the moon is cleft asunder.
But if they see a Sign, they turn away, and say, "This is (but) transient magic."
Early traditions and stories explain this verse as a miracle performed by Muhammad, following requests of some members of the Quraysh.   Most early and medieval Muslim commentators accepted the authenticity of those traditions, which allude to the moon-splitting as a historical event.  The following verse 54:2, "But if they see a Sign, they turn away, and say, 'This is (but) transient magic'" is taken in the support of this view.  The post-classical commentator Ibn Kathir provides a list of the early traditions mentioning the incident: A tradition transmitted on the authority of Anas bin Malik states that Muhammad split the moon after the pagan Meccans asked for a miracle. Another tradition from Malik transmitted through other chains of narrations, mentions that the mount Nur was visible between the two parts of the moon (Mount Nur is located in Hijaz. Muslims believe that Muhammad received his first revelations from God in a cave on this mountain, Cave of Hira'). A tradition narrated on the authority of Jubayr ibn Mut'im with a single chain of transmission says that the two parts of the moon stood on two mountains. This tradition further states that the Meccan responded by saying "Muhammad has taken us by his magic. If he was able to take us by magic, he will not be able to do so with all people." Traditions transmitted on the authority of Ibn Abbas briefly mention the incident and do not provide much details.  Traditions transmitted on the authority of Abdullah bin Masud describe the incident as follows:  
We were along with God's Messenger at Mina, that moon was split up into two. One of its parts was behind the mountain and the other one was on this side of the mountain. God's Messenger said to us: Bear witness to this 039:6725
The narrative was used by some later Muslims to convince others of the prophethood of Muhammad. Annemarie Schimmel for example quotes the following from Muslim scholar Qadi Iyad who worked in the 12th century: 
It has not been said of any people on the earth that the moon was observed that night such that it could be stated that it was not split. Even if this had been reported from many different places, so that one would have to exclude the possibility that all agreed upon a lie, yet, we would not accept this as proof to the contrary, for the moon is not seen in the same way by different people. An eclipse is visible in one country but not in the other one in one place it is total, in the other one only partial.
The Muslim scholar Yusuf Ali provides three different interpretations of the verse. He holds that perhaps all three are applicable to the verse: Moon once appeared cleft asunder at the time of Muhammad in order to convince the unbelievers. It will split again when the day of judgment approaches (here the prophetic past tense is taken to indicate the future). Yusuf Ali connects this incident with the disruption of the solar system mentioned in 75:8-9. Lastly, he says that the verses can be metaphorical, meaning that the matter has become clear as the moon. 
Some dissenting commentators who do not accept the miracle narration believe that the verse only refers to the splitting of the moon at the day of judgment.   Likewise, M. A. S. Abdel Haleem writes:
The Arabic uses the past tense, as if that Day were already here, to help the reader/listener imagine how it will be. Some traditional commentators hold the view that this describes an actual event at the time of the Prophet, but it clearly refers to the end of the world. 
Western historians such as A .J. Wensinck and Denis Gril, reject the historicity of the miracle arguing that the Qur'an itself denies miracles, in their traditional sense, in connection with Muhammad.  
Quran 54:1–2 was part of the debate between medieval Muslim theologians and Muslims philosophers over the issue of the inviolability of heavenly bodies. The philosophers held that nature was composed of four fundamental elements: earth, air, fire, and water. These philosophers however held that the composition of heavenly bodies were different. This belief was based on the observation that the motion of heavenly bodies, unlike that of terrestrial bodies, was circular and without any beginnings or ends. This appearance of eternity in the heavenly bodies, led the philosophers to conclude that the heavens were inviolable. Theologians on the other hand proposed their own conception of the terrestrial matter: the nature was composed of uniform atoms that were re-created at every instant by God (the latter idea was added to defend God's omnipotence against the encroachment of the independent secondary causes). According to this conception, the heavenly bodies were essentially the same as the terrestrial bodies, and thus could be pierced. 
In order to deal with implication of the traditional understanding of the Quranic verse 54:1–2, some philosophers argued that the verse should be interpreted metaphorically (e.g. the verse could have referred to a partial lunar eclipse in which then Earth obscured part of the Moon). 
This tradition has inspired many Muslim poets, especially in India.  In poetical language Muhammad is sometimes equated with the Sun or the morning light. As such, part of a poem from Sana'i, a renowned early twelfth century Persian Sufi poet, reads: "the sun should split the moon in two".  Jalal ad-Din Rumi, a renowned Persian poet and mystic, in one of his poems conveys the idea that to be split by the Muhammad's finger is the greatest bliss the lowly moon can hope for and a devoted believer splits the moon with Muhammad's finger.  Elaborating on this idea, Abd ar-Rahman Jami, one of the classical poets and mystics of Persia, plays with the shapes and numerical values of Arabic letters in a complicated way: the full moon, Jami says, resembles the Arabic letter for M, a circular mīm ( ـمـ ), with the numerical value 40. When Muhammad split the moon, its two halves each became like a crescent-shaped nūn ( ن ) (the Arabic letter for N) whose numerical value is 50 each. This would mean that, thanks to the miracle, the value of moon had increased. 
In another place Rumi, according to Schimmel, alludes to two miracles attributed to Muhammad in tradition, i.e. the splitting of the moon (which shows the futility of man's scientific approach to nature), and the other that Muhammad was illiterate. 
After Apollo mission photographs were published of Rima Ariadaeus in 2016, the 300 km-long rift line on the surface of the Moon,  it was claimed by Muslims on some internet sites and social media that this was result of the splitting mentioned in the Quran.   In 2010, NASA scientist Brad Bailey was asked about this and replied "My recommendation is to not believe everything you read on the internet. Peer-reviewed papers are the only scientifically valid sources of information out there. No current scientific evidence reports that the Moon was split into two (or more) parts and then reassembled at any point in the past." 
What Would Happen If There Were No Moon?
(Inside Science TV) -- The moon -- it can appear full, shining like a beacon in the night or just a sliver of a nightlight. Still, it's always there.
But what if we didn't have a moon?
Here's the top five things we would miss without it.
1. Nights would be much, much darker. The next brightest object in the night sky is Venus. But it still wouldn't be enough to light up the sky. A full moon is nearly two thousand times brighter than Venus is at its brightest.
2. Without the moon, a day on earth would only last six to twelve hours. There could be more than a thousand days in one year! That's because the Earth's rotation slows down over time thanks to the gravitational force -- or pull of the moon -- and without it, days would go by in a blink.
More About the Moon from Inside Science
3. A moonless earth would also change the size of ocean tides -- making them about one-third as high as they are now.
What Would Happen to Earth if our Moon Were Obliterated? - History
What would happen if Earth had more than one moon? Would our tides, or weather, or seasons, or body cycles change if we did have more than one?
The tides on Earth would definitely be affected by the presence of other moons, because the Moon (and also the Sun) is the reason why we experience tides at all. If they were many moons around Earth, the amplitude of the tides might be smaller or larger, since the effects of each other could partially cancel out or add up. There could also be more than two high tides per day, and the cycle of the tides could be less regular than it is.
If Earth had more moons, there would also be more solar eclipses. These two things would probaly be the more noticeable effects. That's because the seasons and the variation of temperature over the course of the year are caused by the orbit of the Earth around the Sun, and the fact that the Earth's rotation axis is tilted. Unless the presence of more moons could affect one of these, we shouldn't notice any chages in the course of the seasons. As for our body cycles, there are no scientific theories relating them to the presence of the Moon.
This page was last updated on July 18, 2015.
About the Author
Amelie is working on ways to detect the signals of galaxies from radio maps.
One heck of a time
A record of Earth’s development is written in rocks. But flowing air, ice, and water chew up old rocks, while trenches deep under water annihilate ancient crust. All of that action means much of the planet’s geological history has been purged from existence. The epochs shortly after Earth’s formation are particularly obscure, but geologists often assume that, for a considerable length of time, it was a little dull here: a stagnant, rocky surface under a hazy volcanic sky.
It’s puzzling, then, that in Australia, a selection of near-indestructible crystals called zircons have been found, through the measurement of their radioactive decay, to be 4.4 billion years old. These minerals are commonly found in chemically complex rocks, such as granites, and scientists have never come to a consensus about how a geologically lackluster Earth could have crafted such advanced materials.
Perhaps, thought Lock, the moon had something to do with it.
Our moon appeared just after Earth was put together. A planet-sized object slammed into Earth and created a ring of lunar building blocks that clumped together into a roughly spherical natural satellite. Simulations indicate that this new companion orbited far closer to the planet than it does today. This would have had an effect on Earth’s rotation, but previous studies hadn’t looked into the wider consequences. Curious, Lock created his own simulations to see how the moon’s effect on Earth’s rotation might have played out.
The results were due to be presented at the 51st Lunar and Planetary Science Conference in March, but the coronavirus pandemic canceled the in-person gathering in Texas. The summary of the results paints a remarkable picture, framing our planet’s dance companion as one heck of an architect.
A Brief History of Earth: How it All Began
A series exploring the natural history of Earth, beginning with the formation of our Solar System, moving on through asteroid impacts and mass extinctions, and ending with the human impact on the environment.
Earthrise, as seen from the Moon. Credit: mvannorden/Flickr, CC BY 2.0
The relatively calm region of space we occupy in the Solar System today belies a fiery, violent past, and a spine-chilling future. This series explores the geological and natural history of Earth, beginning with the formation of our Solar System, moving on through asteroid impacts and mass extinctions, and ending with the human impact on the environment today. To really grasp the magnitude of the changes our planet has undergone, we need to speed through immense timescales, pausing at important milestones. And this article, the first of the series, starts at the very beginning.
Some 4.6 billion years ago, a giant cloud of gas, called a nebula, collapsed into itself because of its mass and crushed all the gassy material in it into a plane, even as it was constantly spinning. This disc of material is called the protoplanetary disc. Over a period of a hundred thousand years after the collapse, the Sun was formed at the center of this disc, with the rest of the nebular gas swirling around it. Nearly 98% of this gas was just hydrogen and helium. (Our Sun constitutes 98% of the mass of our Solar System today.) Gases and other materials in this protoplanetary disc outside of the Sun started clumping together at various spots. Constant collisions between these bodies formed miniature planets, called planetesimals. These seeds of planets eventually grew in size by pulling more material in due to growing gravitational forces, a process called accretion , to become true planets within 100,000 years after the Sun’s formation. The gas giants, Jupiter and Saturn, and the ice giants, Uranus and Neptune, formed much faster than the four terrestrial planets: Mercury, Venus, Earth, and Mars, did.
Approximately 4.54 billion years ago, a Mars-sized body slammed into the newly formed Earth, partially liquifying the surface and ejecting molten debris into space. This ejecta remained as a ring around our planet for a few months, before coalescing and forming the Moon. Residual gases were still swirling slowly around the Sun, causing streams and waves in space. Elephantine Jupiter got caught up in these currents and started moving inward toward the Sun. The movement of this giant, with its powerful gravity wreaking havoc as it danced around, dislodged asteroids and sent them flying inwards into the planets. In the next few million years, the Earth and other terrestrial planets went through a period of constant battering by asteroids and other smaller bodies. This period in the solar system’s history is called the Late Heavy Bombardment. Fortunately, Saturn soon started pulling Jupiter back, toward where it is today, even as the Solar wind stripped away all of the residual gas in the solar system into interstellar space.
At this point, Earth was still cooling from the formation of the Moon, and the period of bombardment kept it agitated and volcanically active. At some point, asteroids or comets containing water ice slammed into the Earth, thereby bringing a lot of water vapor to the Earth. Once the Earth cooled, this vapour condensed and fell as rain on the planet. Volcanic activity still continued and even under the newly forming oceans, super-volcanoes persisted. Lava constantly flowed on the surface for nearly 700 million years.
We know all of these intricate details to a near approximate date by studying rocks on our planet. Rocks hold records of all kinds of transitions that they have undergone. They record their own formation and grow over millions of years, keeping evidence of life and planet activity within. The field of geology that studies and dates rock layers is called Stratigraphy. This helps scientists figure out the age of a lot of geological processes, and has enabled them to put together a geological time scale for our Earth.
The geological timescale above is a representation of time elapsed after the formation of earth, divided into slices, each differentiated by a geological event whose record is held in rock samples. Geological time is primarily divided into eons, which are divided into eras, which are further divided into periods. A discussion of these three scales falls within the scope of this series. However, for the sake of completeness, it needs to be specified that periods are further divided into epochs, and epochs into ages, while eons are grouped into super-eons.
The first three eons are grouped under the Precambrian super-eon . The fourth eon, called the Phanerozoic, is ongoing. Although the first three eons together account for most of Earth’s history, stretching out for nearly four billion years, there was little of note in terms of biological activity or geological diversity. So, in representations such as the table above, they are usually collectively called the Precambrian. It contains the Hadeon eon, when Earth was forming and the Late Heavy Bombardment took place the Archeon eon, when water first showed up and the first lifeforms evolved the Proterozoic eon, when the first multicellular organisms appeared and Earth’s atmosphere received oxygen for the first time as a result of the proliferation of cyanobacteria.
The early years of the Precambrian saw the formation of the Moon, a molten Earth slowly cooling down, and the planet getting battered by small runaway bodies. Water vapour in the atmosphere from asteroid and comet impacts started to condense and rain down on the planet as liquid water. Oceans formed amid heavy volcanic activity. Portions of the surface periodically cooled off to form occasional landmasses, but they would immediately be swallowed up by lava. Then, approximately 100 million years after the Earth formed, the temperatures had become stable enough for a crust to form and survive. The atmosphere was heavy and toxic, with almost no oxygen but with large amounts of carbon dioxide, nitrogen and sulphur due to volcanic activity.
Within another half a million years, multiple tiny landmasses had been born. These went on to become the centre around which present-day continents formed. The oldest known rocks on Earth are from this period , now in Australia, dating back to 4.4 billion years ago.
sandstone rocks in Jack Hills in Western Australia, in which 4.4 billion year old zircon crystals were found. Source: Author provided
Towards the middle of the Precambrian, the earth had cooled sufficiently. In the atmosphere, there was still no oxygen. The oxygen on our planet today is produced and sustained solely by plant life. This lack of oxygen implied a lack of ozone to protect the earth, which exposed the Earth to UV rays from the sun. However, the earth’s atmosphere could be preserved because its magnetic field had begun to form. This protected the atmosphere from being stripped away by the solar wind (as the atmosphere of Mars was).
Around 3.5 billion years ago (bya), two supercontinents, called Vaalbara and Ur formed within half a billion years of each other. These landmasses were actually quite small, probably about the size of India. But since they were the only landmasses around, they are called “supercontinents”.
The lack of oxygen in the atmosphere did not mean a lack of life, though. Life began on Earth in the early Precambrian, 4.1 bya, when earth had just started cooling . Gems from this time period, called zircons, have very specific carbon ratios, and possibly show evidence of biological activity combined with water . It is commonly assumed and accepted that one of the main causes of the creation of life is the presence of large oceans. Liquid water is considered to be a universal solvent, which means that it can transport all kinds of nutrients to all corners of the planet, enabling even the remotest locations to support life. Thanks to its almost magical properties, the very presence of liquid water on a body is a giant attraction for space exploration today.
The location of Ur. Source: Author provided
Apart from nitrogen, methane, and ammonia, volcanoes also released a lot of carbon into the atmosphere. Coupled with the condensing water vapor, earth became a crucible for the formation of life in this early environment known as primordial soup . Simple cells are believed formed in such a wet environment. : Small ponds that could have been struck by lightning or another form of energy and deep sea hydrothermal vents that contain the energy and nutrients to synthesize a cellular structure could have been likely location for the formation of life. Scientists have not been able to artificially recreate the synthesis of life. How life came to be remains an enduring mystery.
Nevertheless, water was the only medium to contain the earliest lifeforms, which were unicellular. These could simply absorb nutrients from their surroundings and break it down in their system for sustenance. This very primitive process made life dependent on nutrients from rocks and water. But towards the second half of the Precambrian, early unicellular bacteria started absorbing infrared light instead of visible light and started to emit oxygen. This was primitive photosynthesis.
Photosynthesis enabled organisms to create their own food for the first time. This mechanism offered a great advantage and accelerated the growth of life: from prokaryotes to eukaryotes that started reproducing sexually 1.2 bya, to multicellular life. Banded iron formations – layers of rock from the ocean showing pulses of iron oxide deposits due to reaction with oxygen – dating back to 3.7 bya exist today. These show evidence that large quantities of oxygen were pumped into water at intervals a phenomenon that is explicable only as a biological process. More biochemical rocks, called stromatolites, that were formed due to microorganisms trapping sand grains to build colonies, date to 3.5 bya. The most solid evidence of photosynthesis, however, dates back to 2.4 bya when cyanobacteria flourished, infusing massive quantities of oxygen into the air. So, two billion years after the earth formed, there was finally a constant supply of oxygen in the air for the first time.
Banded iron formation in the Mesabi Range, Minnesota. Credit: sas.rochester.edu
At around the same time, a new supercontinent called Kenorland was formed, while Vaalbara broke up, with parts of it ending up in today’s Australia and Africa. Kenorland was much larger than either Vaalbara or Ur. It was as big as Africa and existed somewhere near the equator for a hundred million years before breaking up.
Meanwhile, the earth’s atmosphere underwent a drastic change as photosynthesis increased. It evolved from a nauseating mixture of carbon monoxide, methane, ammonia, and nitrogen, to becoming much more toxic with plenty of pure oxygen that was anathema to the existing lifeforms. Pure oxygen today still remains toxic to all life, including humans. Since cyanobacteria were aquatic they saturated the oceans with oxygen too. This was called the Great Oxygenation Event and occurred 2.3 bya. The rise in levels of this new gas in earth’s ecosystem led to two major events on Earth: the first extinction event and the first ice age.
An Extinction Event, more commonly known as a mass extinction , is the the extinction of a large number of species within a short period of geological time. There have been 24 extinction events in all of Earth’s history – before humans came around 200,000 years ago. Five of these were particularly destructive, with detailed, well documented evidence of their occurrence and repercussions. These major extinction events are called the Big Five.
Occurrence of mass-extinction events. Source: Author provided
Mass extinctions always occur after a sudden, rapid, and uncontrollable change in global climate – which is obvious because only such widespread changes can kill off diverse species spread out over land and water in a short period of time. Conversely, mass extinctions could also affect the global climate as disappearance of a majority of life on Earth could upset the oxygen balance.
As photosynthesis increased, there were very few lifeforms that were able to consume enough of this new oxygen. There was nowhere for the toxic oxygen to go because there was no oxygen sink . As the oxygen content in the atmosphere and oceans increased, early life that was just forming was also dying away rapidly. This is why the Great Oxygenation Event also became the first known extinction event.
The other effect the oxygen catastrophe had was the formation of glaciers. The rise of oxygen naturally removed a lot of greenhouse gases from the atmosphere, most notably methane. Oxygen lowers temperatures, which is why wooded areas are so much cooler than cities today. The saturation of oxygen in the atmosphere lowered the overall temperature to 5°C lower than today and removed the ability of the atmosphere to keep the planet warm. Temperatures started falling steeply, heralding an ice age .
An ice age is a period, extending to millions of years, of lowered temperature on the Earth. A characteristic feature of an ice age is the presence of continental glaciers and polar ice caps. An ice age is composed of periods of extreme cold, called glaciation periods , marked by the appearance of large ice sheets and glaciers over continents. These alternate within the same ice age with periods of warmth, called inter-glaciation periods , where the ice sheets are confined to the poles.
The ice age caused due to the Great Oxygenation Event was the first of the five ice ages the Earth has seen and is called the Huronian Ice Age. We are currently in the middle of the fifth ice age’s inter-glaciation period.
The next instalment in this series discusses the Huronian ice age, the Cryogenian or the second ice age, the breakup of the Kenorland supercontinent and the formation of new supercontinents, as well as the first of the five major mass extinctions, and gamma ray bursts.List of site sources >>>