National Geographic Daily News
An illustration of the moon being formed.

The moon was likely formed when a Mars-size object hit Earth and blew parts of the planet into space.

ART BY DANA BERRY. SOURCE: ROBIN CANUP, SWRI

Jane J. Lee

National Geographic News

Published April 2, 2014

Earth's moon is some 4.47 billion years old, its birthday having come about 95 million years after the formation of the solar system. This means Earth's closest companion is some 60 million years younger than previously estimated.

The revised figure comes from a new study that sidesteps a long-running debate about the age of our moon and agrees with planetary scientists arguing for a late-forming moon. And the new method researchers used to arrive at their conclusion does away with a lot of the questions about the traditional ways of calculating its age. (See "The Moon's Mystery: Scientists Debate How It Formed.")

Usually, scientists estimate our moon's age by using the radioactive decay of elements like uranium, says John Chambers, a planetary scientist at the Carnegie Institution for Science in Washington, D.C.

By taking an element with a known rate of decay, and knowing its concentration in moon rocks or the Earth's surface, researchers can back-calculate a time for when the material formed. But there are a lot of different radioactive materials that can give you different timelines, says Chambers, who was not involved in the study.

"Geochemists get into a lot of fights with each other trying to determine what these ages mean," says Seth Jacobson, a planetary scientist at the Observatoire de la Côte d'Azur in Nice, France, and co-author of the study.

The new study, published today in the journal Nature, does away with this entirely by coming at the age question from a different angle.

Planetary Weight Gain

It's generally accepted that the moon formed near the end of Earth's construction, says Jacobson, when an object about the same mass as Mars hit our planet and blew parts of both bodies into space. Those bits eventually coalesced into the moon.

After that last giant impact, Earth added weight, but it came from impacts by smaller objects about the size of asteroids like Vesta, he says. Jacobson and colleagues used this later weight gain to calculate when the Mars-size object smacked into the Earth.

Their new method relies on the fact that elements in the Earth's crust that have an affinity for combining with iron, such as platinum or iridium, arrived after the last giant impact.

"When the moon-forming event occurs, this melts the entire surface of the Earth," says Jacobson. All the iron present near the surface sinks into the Earth's core, taking iron-loving elements along with it.

Any such elements now present in the Earth's surface arrived on objects that hit our planet after its core formed.

This later-forming time line for the moon is reasonable, says William Hartmann, a researcher at the Planetary Science Institute in Tucson, Arizona. However, he said that the new study might rely too much on the idea of using the last giant impact as a marker for when such events occurred in Earth's history.

"What people frequently forget in this field is that you never have just one big impact," says Hartmann, who first proposed the giant impact theory of the moon's formation. "We have to worry about how big the next biggest impact was," and whether that impact blurred the effects of the previous giant impact.

A Cascade of Implications

This evidence for a later-forming moon means that Earth's impact history was more violent than previously thought, says Jacobson. (Read "Our Solar System" in National Geographic magazine.)

The change in our planet's bombardment rate, he says, also means a change in the amount of energy that went into Earth's atmosphere and oceans. It also has implications for the history of our planet's surface temperature, which is important because liquid water couldn't form until the surface cooled enough. (Learn about how Earth got its atmosphere and its oceans.)

These results, which suggest the Earth formed nearly 100 million years after our solar system was born, also throw a monkey wrench into how scientists think about the formation of other rocky planets like Mars and Venus, Jacobson says.

Mars formed a few million years after the birth of the solar system, while Earth clearly took longer, he explains. If Venus formed on a timeline similar to that of Mars, then that would be a "huge puzzle" since Venus and Earth are so similar in terms of mass and orbit.

But these are open questions for future research, Jacobson says. For now, he and his colleagues will continue studying how planets in our solar system formed.

Follow Jane J. Lee on Twitter.

29 comments
Johan Lindeberg
Johan Lindeberg

I have heard theories that advocate that the moon was on a near collision course but became instead a satellite to earth

Johan Lindeberg
Johan Lindeberg

"Geochemists get into a lot of fights with each other trying to determine what these ages mean,"

Matjaž Ciglar
Matjaž Ciglar

The Moon is not a moon it is a planet orbiting a Sun. On it's path around the Sun, Moon is wobbling because of Earth week gravitational pull.

When Moon is closest to the Sun, Earth pull starts to slow down Moon and therefore moon starts to drift apart from Sun until farthest point. At that point Earth start to accelerate Moon until a full circle is completed approximately within one month. Sun's gravitional force on the Moon is 2,25 times greater than Earth's.

madison upchurch
madison upchurch

there is no such thing as the big bang or anything else .God created the earth and solar system and everything around it. Jesus loves you and . God's NOT dead. 

Георги Кънев
Георги Кънев

The Moon was born from the Earth in the early live days of the two. The proof of such assertion is shown in the part I USM www.kanevuniverse.com where is calculated the centripetal acceleration on the Moon’s surface which exactly coincides with the experimental one, through the following newly found out rule there: To distinguish the planets from other objects in the solar system, there it isn’t enough to estimate the form of orbit (elliptic or more-less circuit one) and the mass of object, but also to calculate the own centripetal acceleration via the field formula: .....

Eric Sorensen
Eric Sorensen

There are two types of imagination: The gift of imagination that allows us to understand scientific ideas based on measurable observations (the human mind can envision superclusters of galaxies and quarks); or the imagination that doesn't understand what it sees and makes something up. The two are not equivalent

Jonathan Krailller
Jonathan Krailller

I find this article interesting not because of the argument of when the moon was formed but how we measure the earth slowly gaining mass due to colision from asteroids and that these asteroids carried with them Iron and other metals which is the main reason for deposits.  I would like to know what the average mass gain per year is and whether there we are lucky that we have seen minimal asteroid impacts over the past thousand years or if that is due to our solar system.

Alvin Nurse
Alvin Nurse

The price of "certainty" is too much ...I appreciate the new data as it comes in...!


Jeffrey Bothen
Jeffrey Bothen

According to Genesis "God made two great lights; the greater light to rule the day, and the lesser light to rule the night" on the fourth day, as distinguished from the Light that was present at the beginning.From this we may reasonably conclude that the 24 hour day we experience was part of the creation event, occurring just past creation's mid-point.Further, it would seem that the days referenced in the Genesis account are not measurable as our days are on our wonderful bit of Creation, but are likely far more lengthy periods and, if we accept that time is relative; subject to the movement of bodies with mass and their gravity, then the days of creation were likely not of uniform length in any way we could understand.It is tenacious hubris when people think God or Creation can be measured with a clock or calendar.After all time is part of creation and the Creator is not subject to time.

The point is that the estimate that the Moon is 60 million years younger than the Earth is not necessarily incompatible with Genesis, nor particularly relevant to it.In my 60 years I have been instructed that the Earth and the Moon were formed together from cosmic dust, that the Earth “snagged” an asteroid – bumped from the asteroid belt, and now there is this latest scientific speculation; a collision of bodies.I suspect if we ever get back into space a new and better theory might gain currency; I should live so long.

Clark Thomas
Clark Thomas

Silly folks, don't you know that snow happens when God has dandruff; rain happens when God's bladder is full -- and large asteroids hit Earth when God's colon is full?  That's all you ever need to know.

Richard Bethell
Richard Bethell

@Jeffrey Bothen  At the time the Moon was formed, the Earth had a four hour day. 24 hour days are a very recent phenomenon on Earth, caused by the slowing of Earth's spin by the conservation of angular momentum in the Earth Moon system.

Tyrone Jackson
Tyrone Jackson

If you want to believe that a creation story made up by Taliban-like people whose knowledge of the Universe was so poor that most of their children died before adulthood, and if they reached adulthood, died on average at less than 40 years of age (and hence the very sow rate of population growth during all but the last couple centuries), go right a head.

The bottom line is that the "change" talked about here of 60M years out of 4.47B years (4,470M years) is just a 1.3% "correction" to the timeline. It's only significant to us academics.

Scott Sinnock
Scott Sinnock

@Randy murrah NO, NO, NO, you have it all wrong, the earth formed 4,735,273,303 years ago at 3:30 in the afternoon plus or minus13.6 seconds at 95% confidence (if, of course, there had been a sun back then to measure a year, but we can assume our sun has spun infinitely at the same rate, or at least a cesium clock has ticked the same by which we now measure a year). Which means that was really the 4th day of the universe.

Matjaž Ciglar
Matjaž Ciglar

@Tyrone Jackson Please don't compare Taliban people with people like Jeffery, they are much more noble people.

Randy murrah
Randy murrah

@Tyrone Jackson The last time I checked, the creation account was not written by a bunch of "Taliban-like" people that died be fore adulthood.  In fact, due to the firmament that was in place around the earth in pre-flood times, people lived to be hundreds of years old.  The account of creation was written by Moses under the inspiration of God.  After much study on the matter, that is what I have come to believe.  You see, if you study nature, you eventually come to the conclusion that intelligent design is in force here.

Randy murrah
Randy murrah

@Scott Sinnock Next year all the scientists will be blabbering about a new theory on the age of the moon or sun or earth.  They will struggle with changing their thought process and spend countless hours fondling their slide rules to validate the new thinking.  Me,  well, I won't trouble myself with such because in the grand scheme of things.... IT DON'T MATTER.  It is said that A man with two watches never knows what time it really is.  I prefer to carry only one watch.  That gets me close enough.

Eric Aasen
Eric Aasen

@Randy murrah The last time i checked, the bible was written about our sun, which is our creation... and if you have any intelligence at all..? Evolution created intelligent design..

N A
N A

@Randy murrah @Tyrone JacksonIt was written by a bunch of noobs who didn't know that Earth went around the Sun, or what germs were. They didn't know the Earth was nearly a sphere, they didn't know  what an electron was.


Yet somehow they knew about the universe's creator? Sounds legit.

James Kleatsch
James Kleatsch

@Randy murrah @Tyrone Jackson Hello, lets just separate church from science here a little bit.Church always wins this kind of discussion because it doesn't need to be proven and doesn't have to rely on facts at all that's why it's a belief system not a system based on facts ever! While science is fact based and has to have evidence to back it up, it's working at a disadvantage from the start because how do you defend against "I believe" with just mere facts when the belief can change to support their cause at the drop of a hat.

Amir Patel
Amir Patel

@Randy your comment is a complete fail lol the artcile clearly states:

"
A germ is now thought to be responsible for killing 95% of the planet's species some 250 million years ago, by belching gargantuan quantities of methane, in what's known as the Permian Extinction." considering dinosaurs didn't exists back 250 million years ago this would be talking about the age when the trilobites roamed the ocean depths. The extinction event of the dinosaurs happened during the Cretaceous–Paleogene not the Permian event which was separated by at least 200 million years.  Even better though the article continues to state:
"In the global catastrophe triggered by the primitive bacteria 252 million years ago, upwards of 90 percent of marine species and 70 percent of land animals were wiped out.""The scale of THIS calamity made the one that doomed the dinosaurs 65 million years ago - a six-mile wide asteroid smacking the planet - seem like a picnic by comparison."
Some how in the first four paragraph of the article YOU posted a link to, you were totally proven wrong. And not only that, you have shown us you cant even read a short article properly.

Scott Sinnock
Scott Sinnock

@Anny Dean Yeah, I know, Paleogene; I got to get with it, but what do we do with all those red Tertiary deposits that are mapped everywhere?

Anny Dean
Anny Dean

@Randy murrah Please do not spread so much ignorance over our screens. It is almost obscene.

Dear Randy, the article in question is about the Permian–Triassic extinction event not the Cretaceous–Paleogene extinction event. (Just 200 million years difference.)

Scott Sinnock
Scott Sinnock

@Diane Merriam @Randy murrah@Scott Sinnock "Science has ways of paying off in surprising ways" perhaps like the destruction of the human soul while preserving the body, as some have said.

Scott Sinnock
Scott Sinnock

@Randy murrah @Scott Sinnock Yes, I agree, one watch is plenty, but none is even better.

Diane Merriam
Diane Merriam

@Randy murrah @Scott Sinnock  Some people asked "What difference does it make what killed the dinosaurs?" If we hadn't kept digging into that question, that big asteroid may have never been found and we would have never worried about looking for other  Near Earth Objects that at some point *are* on a trajectory to hit us in the future . Good to know that ahead of time so we can change the trajectory enough to protect ourselves.


"Pure" science research has a way of paying off in surprising ways.

Share

How to Feed Our Growing Planet

  • Feed the World

    Feed the World

    National Geographic explores how we can feed the growing population without overwhelming the planet in our food series.

See blogs, stories, photos, and news »

The Innovators Project

See more innovators »

Latest News Video

See more videos »

See Us on Google Glass

Shop Our Space Collection

  • Be the First to Own <i>Cosmos: A Spacetime Odyssey</i>

    Be the First to Own Cosmos: A Spacetime Odyssey

    The updated companion book to Carl Sagan's Cosmos, featuring a new forward by Neil deGrasse Tyson is now available. Proceeds support our mission programs, which protect species, habitats, and cultures.

Shop Now »