ROUND AND ROUND: Earth spins through the sun's rays much slower than it once did.
Image: © JAXA/NHK
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Gravity's Engines
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The summer solstice that falls this year on June 21 marks the longest day of the year in the Northern Hemisphere, sunlight-wise. Almost imperceptibly, however, Earth's day–night cycle—one rotation on its axis—is growing longer year by year, and has been for most of the planet's history.
Forces from afar conspire to put the brakes on our spinning world—ocean tides generated by both the moon and sun's gravity add 1.7 milliseconds to the length of a day each century, although that figure changes on geologic timescales. The moon is slowly spiraling away from Earth as it drives day-stretching tides, a phenomenon recorded in rocks and fossils that provides clues to the satellite's origin and ultimate fate. "You're putting energy into the moon's orbit and taking it out of the Earth's spin," says James Williams, a senior research scientist at NASA's Jet Propulsion Laboratory in Pasadena, Calif.
The moon's gravity generates tides by pulling hardest on the side of Earth facing it. This attraction causes the planet to bulge, especially in its malleable oceans. (The sun affects tides in the same way, although in comparison due to its great distance they amount to only about a fifth of the lunar influence on our planetary pirouette.) Earth rotates faster than the moon orbits it, so the watery tidal bulge travels ahead of the moon's relative position. This displaced mass gravitationally tugs the moon forward, imparting energy and giving the satellite an orbital boost, whereas friction along the seafloor curbs Earth's rotation.
Williams has studied how fast the moon is corkscrewing away by shining lasers from Earth at prism-shaped reflectors placed on the lunar surface in the late 1960s and early 1970s by U.S. astronauts and unmanned Russian probes. Changes in the beam's round-trip time reveal the moon's recession rate—3.8 centimeters per year—which, largely due to the orientation of Earth's landmasses and its effect on oceanic sloshing, is faster now than in previous epochs, Williams says.
Hints of inconsistent Earthly timekeeping come through natural calendars preserved in fossils. Corals, for example, go through daily and seasonal growing cycles that form bands akin to growth rings in trees; counting them shows how many days passed in a year. In the early Carboniferous period some 350 million years ago an Earth year was around 385 days, ancient corals indicate, meaning not that it took longer for the planet to revolve around the sun, but that a day–night cycle was less than 23 hours long.
Sedimentary rocks such as sandstone also testify to the quicker days of yore. As moon-spawned tides wash over rocks they deposit mineral specks, layer upon layer. In southern Australia, for example, these vertically accumulating tidal "rhythmites" have pegged an Earth day at 21.9 hours some 620 million years ago. This equates to a 400-day year, although other estimates suggest even brisker daily rotations then.
"As you start going further back in time, the records get difficult to interpret," says Kurt Lambeck, a geophysicist at the Australian National University in Canberra. Lambeck, who serves as president of the Australian Academy of Science, wrote a book on the subject, The Earth's Variable Rotation: Geophysical Causes and Consequences, in 1980. "But the records have tended to support a general pattern going back that the number of days in the year increases," Lambeck says.
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33 Comments
Add CommentWouldn't the same argument for the Moon's increased speed fit for the earth's increased speed. Are the tidal influences of the Earth on the Sun's tides a mirror of the Moon on the Earth's tides?
Reply | Report Abuse | Link to this3.8 cm per yr is not much of a measurement and should be subject to an array of errors. How does one separate the sources of variability from this measurement, i.e., changes in the earth's surface and the like?
Reply | Report Abuse | Link to thisI remember research that showed if humans are shut off from outside influence and free to choose waking/sleeping time they move to a 22 hour day, perhaps our body clocks are still on the old day.
Reply | Report Abuse | Link to thisAstrological observatories have detected quasars rotating are enormous speeds in the early stages in their development. At this stage of our planet's evolution we have a 365 day year and a 24 hour biological clock. It seems that from Earth's primal years, how fast would the planet have spun and what was the position of the planet around the sun? If 620 million years ago there was 400 days in the year and 21.9 hours in the day, what was it at the time of the dinosaurs or the first century after the birth of planet Earth?
Reply | Report Abuse | Link to thisHow long will it be for humanity to see a 25 hour day and 360 day year? What is the maximum for the planet's calender and hour in a day, and when will Earth and moon separate? Is the same process going on with the other planets in the solar system, like Venus, Mars, Saturn and Jupiter? What will happen when Luna separates from Earth, how will that effect near-by planets? How will that effect life on Earth?
A sixteen hour work day?
Just wait until the labour unions hear about this!
Reply | Report Abuse | Link to thisThere seems to be a lot of supportive evidence that suggests that all planetary rotational speeds are first on the extreme scale. We had to be, in our infancy a lot closer to the sun than where we are now, and our rotational speed much more extreme than what it is now, too. There is one constant in the universe, and that is change. We as humans have only been around for the past six million years, so we have not been witness to the great geological changes that have taken place in the last 350 million years; let alone the last 10 million years. We are infants in the purest sense of the word, and if we live long enough we will be witness to many great and wondrous changes that will happen in the next 300 million years. How long will a day be and how long will the year be in the next 100 million years? Will humanity still be here to see it all unfold before our non-adolescent eyes?
Reply | Report Abuse | Link to thisOver half a century ago, I remember that we learnt in our Geology classes that the diameter of the earth had been expanding, thus slowing down the rotation around itself.
Reply | Report Abuse | Link to thisThe article does not seem to discuss the "Expanding Earth" hypothesis!
Every day hundreds of tons of dust from outer space falls on the arth. Over the millions of years the earth has grown.That is the reason for the slower spin . Millions of years ago the earth spun faster, there was less gravity and huge plants and animals were the norm.
Reply | Report Abuse | Link to thisIf people are on the average bigger now, it is because of improved diets.
The distance to the sun might have been closer but it could have been the same of what it is now.
Isn't it about time in this discussion for someone to claim that this whole state of affairs is Obama's fault?
Reply | Report Abuse | Link to thisNot only is matter arriving on the Earth, but I understand that water is boiling off. What is the mass balance of the Earth anyway?
Reply | Report Abuse | Link to thisOkay, "hawkeye", I will make the claim...the longer days, about ten minutes in the last 50 years, according to the "Navy Watchdogs" who plot their missions according to the daylight in a day, is Obama's fault because he requested the longer days so he would have more time to fix all the Bush "screw-ups". On the summer solstice, it use to be dusk by 9:05 pm., now it is dusk at 9:20 pm..
Reply | Report Abuse | Link to thisThe collection of biological material with time is also adding mass to our planet at an extraordinary rate.
Reply | Report Abuse | Link to thisI remember hearing/reading about such research - subjects living in caves and such - and as I recall the natural rhythm was found to be more like 25 hours.
Reply | Report Abuse | Link to thisHow the heck does that work, g-man? Are there organisms that are somehow gathering in mass from off-planet beyond the normal random infall?
Reply | Report Abuse | Link to this@galaxy_man, "The collection of biological material with time is also adding mass to our planet at an extraordinary rate." unless living things have found out how to violate the law of conservation of mass, all biological material is derived either from existing bio material or converted by plants, plankton, etc from non-biological materials, i.e. calcium carbonate from CO2. Though the amount of material falling onto the earth from space seems like a great deal, I suspect it makes up a relatively small percentage of the existing mass of the earth. It should be easy to calculate. You will also need to consider the mass lost by the earth in the form of evaporation. I'm sure you will find that the effects of gravity, geological forces like mountain building and continent movement and weather patterns are much greater than the effects caused by an increase in mass and diameter as a result of the accumulation of dust.
Reply | Report Abuse | Link to thisAccording to our calculation, before 2.17 million years, the distance between Sun and Earth was 62902953 kms and that of Sun and Jupiter was 746089634 kms. The distances for Mercury was 15149700 kms, that of Venus 38696418 kms, Mars 118311123 kms and Saturn 1854025209 kms. The distance between Earth and Moon was 4705196 kms. The diameter of the planets starting with Mercury was 2104, 7166, 23236, 10955, 120894 and 214586 kms respectively. The ratio of the orbital periods of Earth and Jupiter was 1: 12. This apperas to be in conformity with the present findings.
Reply | Report Abuse | Link to thisbasudeba.
According to our calculation, before 2.17 million years, the distance between Sun and Earth was 62902953 kms and that of Sun and Jupiter was 746089634 kms. The distances for Mercury was 15149700 kms, that of Venus 38696418 kms, Mars 118311123 kms and Saturn 1854025209 kms. The distance between Earth and Moon was 4705196 kms. The diameter of the planets starting with Mercury was 2104, 7166, 23236, 10955, 120894 and 214586 kms respectively. The ratio of the orbital periods of Earth and Jupiter was 1: 12. This apperas to be in conformity with the present findings.
Reply | Report Abuse | Link to thisbasudeba.
According to our calculations, before 2.17 million years, the distance between Sun and the planets up to Saturn were 15149700, 38696418, 62902953, 118311123, 746089634, 1854025209 kms respectively. The distance between Earth and Moon was 4705196 kms. The diameter of the Sun, the planets and the Moon were 1261942, 2104, 7166, 23236, 10955, 120894, 214586 and 6971 kms respectively. The ratio of the orbital period of Earth and Jupiter was 1: 12. The present findings appear to be in line with our findings.
Reply | Report Abuse | Link to thisbasudeba
Some say tidal energy production will slow down even more the Earth's rotation, but: does this have any consequence?.
Reply | Report Abuse | Link to thisIt seems that Venus, like the Moon, has its rotation linked to the Earth, always showing the same part towards our planet. How can this have happened, with a planet so far away and so big as Venus?
According to other sources about tidal effects of the Moon and Sun, the Moon's gravitational effect causes about 66% of the tides, and the sun about 33%
Reply | Report Abuse | Link to thisScientific American is a lone proponent of the 80% to 20% effect.
I don't think the expanding earth theory is taught anymore.
Reply | Report Abuse | Link to thisThe amount is a lot closer to 20 tonnes per day of dust falling on the Earth.
Reply | Report Abuse | Link to thisYou said the Earth would rotate faster as the ground rose following the melting of the ice sheets. The melting of the ice and consequent flow towards the centre of the Earth would cause the Earth to spin a little faster but the rising of the ground will actually slow the spin down.
Reply | Report Abuse | Link to thisWhile the melting of the ice sheets and consequent flow of water towards the centre of the Earth speeds up the spin rate of the Earth the ground levels rising will tend to slow it down.
Reply | Report Abuse | Link to thisMakes one wonder if there ever was a time when days and nights were almost consecutive.
Reply | Report Abuse | Link to thisMakes you wonder if there was ever a time when days and nights were almost consecutive.
Reply | Report Abuse | Link to thisthis indicates that the earth will stop rotating at some point, not only that but it will spin in the other direction as indicated in the holly books. the sun will rise from the west and that will be the start of the end. many facts are described in those books (coran for example) that only science can proove, every major discovery in nowadays is written in the coran although the age of the coran is 1400 old when no one even know what's beyond it's city or country.
Reply | Report Abuse | Link to thisahmm let me put it this way: if humans loved what theyre doing they say: oh time is running fast i want time extension..but if human hated what theyre doing they think: time is so slow that we want it to end fast... we dwell on good memories and curse the time we had bad times..and wished it never happened.. i have a question..does Earth also have emotions?
Reply | Report Abuse | Link to thismoon spiralling from earth then influence from gravity from other planets and sun could make or has already made the earth and moon touch softly causing the floods covering places like the grand canyon and making the moon look at us with the same face.cause the earth is moving and if the moon is slowed when it is in our way making us catch up to it. on the other hand if gravity is made by mass then asteroid belt should have a relatively big effect on the moon and other objects in space being an object with MASSive proportions (ha-ha I made a funny).
Reply | Report Abuse | Link to thisI remember seeing research which suggests once the Moon and Earth seperate Earth will start to become influenced by Jupiter's gravity which will cause the Earth to "swing" on it's axis. The traditional seasons will cease to exist and all life will eventually die out. This won't happen for another 4 billion years or so it's nothing to worry about yet.
Reply | Report Abuse | Link to thisDoesn't the fact that it is the only planet that rotates in a whole number of hours indicate just a bit more than luck here. All the clues are there it is just a matter of interpreting them to get the result you want.
Reply | Report Abuse | Link to thisThere is the statement about not seeing the forest for the trees. And of course with greater focus, not seeing the tree for the leaves. The measurement assume that the earth land mass isn't/wasn't sinking/moving. We were and still are pulling reasources out of the ground; water, gas, oil, etc. As evident from water wells in Venice, which tends to cause changes in elevations. I find it interesting that the moon is moving at the same rate that the tectonic plates are shifting. "Darn forest". And one more monkey wrench into the works. We are aware that the earths electromagnetic field is growing weaker. Allowing the solar wind to remove move of our atmosphere. As evident in ozone depletion, and solar scientists measurements showing an increase solar radiation reaching our suface. Our thinning atmosphere will also alter these readings. "Darn Monkey?" Good luck with the tree.
Reply | Report Abuse | Link to thisWess
What about the studies with humans in environments where they had no idea of day or night and their "day" stabilized at over 25 hours. Did we evolve in another orbit or on another planet?? Or does the Earth have a different orbit currently than it used to have??
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