How old is the Earth?

I can’t believe we still have to cover this. We know how old the Earth is. The science on this is pretty darn good. It is 4.54 billion years old plus or minus about 1%.

Florida Senator Marco Rubio does not know how old the earth is. Here is what he says about it:

I’m not a scientist, man. I can tell you what recorded history says, I can tell you what the Bible says, but I think that’s a dispute amongst theologians and I think it has nothing to do with the gross domestic product or economic growth of the United States. I think the age of the universe has zero to do with how our economy is going to grow. I’m not a scientist. I don’t think I’m qualified to answer a question like that. At the end of the day, I think there are multiple theories out there on how the universe was created and I think this is a country where people should have the opportunity to teach them all. I think parents should be able to teach their kids what their faith says, what science says. Whether the Earth was created in 7 days, or 7 actual eras, I’m not sure we’ll ever be able to answer that. It’s one of the great mysteries.

Phil Plait has responded with this:

Actually, it’s not a great mystery. It used to be … a century ago. I am a scientist, and I can tell you that nowadays—thanks to science—we know the age to amazing accuracy. The age of the Earth is 4.54 billion years … plus or minus 50 million years. That’s a number known to an accuracy of 99 percent, which is pretty dang good.

Sen. Rubio’s answer, however, is so confused and error-riddled its difficult to know where to start.

And then, Phil goes ahead and addresses that, HERE.

The Maddow Blog also addresses Senator Rubio’s miscarriage of intelligence.

And, the thing is, the actual story about how we know about the age of the earth is not only well established science, but it is intrinsically interesting. Following is from a post I wrote about this a while back, slightly edited:

How old is the earth?

Short answer: 4,540,000,000 Earth-years, plus or minus 1%.

Long answer: We don’t know exactly because direct dating of the earliest material on the surface of the Earth will only tell use a minimum age; Prior to that, the Earth’s surface was probably molten, and even after that, it may be that the earliest non-molten material has been recycled into the planet’s interior by tectonic processes. Also, the earth is a big round ball of stuff that condensed into this shape from part of a large disk-shaped blob of stuff known as the Solar Nebula. When exactly, given this, did the Earth become the Earth? Since the process took millions of years, we can’t pinpoint the age of the Earth more exactly than a certain range.

What are the oldest rocks?

The oldest rock formations on Earth are between about 3.8 and 3.9 billion years old., but there are older bits of more ancient rocks that were incorporated into these early rocks, and they date to something closer to 4.4 billion years old. These and other early materials are dated primarily using a variety of parent-daughter radiometric techniques, with the most effective for this time period being a lead-lead system.

Since rock from the time of the Earth’s formation isn’t available (because it didn’t really exist or was gobbled up in the fiery beginnings of the big round ball) the preferred method of dating the Earth is to calculate the age of meteorites. The earliest meteorites essentially date the condensation of materials in the solar system into the planets, and thus, the date of these meteorites indicates the date of the early Earth. (The Earth existed prior to this condensation in the form of whatever parts of the early solar nebula would eventually condense into this particular planet, of course.)

Meteorites from other planets?

Some meteorites are known to be fragments of Mars, so the oldest dates among these can also verify the date of accretion of material into planets in our solar system.

Rocks from the moon have not been remelted or otherwise messed up by tectonic processes and therefore would provide an excellent estimate of the age of the Earth as well. Also, since there is no real weathering of rocks on the moon, methods other than parent-daughter decay can be used, such as Fission Track dating (the older a rock, the more cosmic rays pass through it, blasting tiny little tracks in the otherwise homogeneous matrix).

Zeroing in on the age of the earth

There are hundreds of published dates of various older materials, but the following table gives a reasonable summary of some of the more important dates, culled from various sources (see list of references below):


If we chart this on a graph, we see one date that is much earlier than all the other dates, and a few that are younger.


The younger dates are simply of materials that we don’t think date the Earth’s formation, but that we know would post date it by not much. These dates verify the earlier cluster of dates that would correspond to the actual formation of the planet. The single earlier date is an obvious outlier.

Taking this series of dates, notice that the oldest (non-outlier) dates are about four and a half billion years old. As stated in the short answer.

Further information about the age of the Earth:

Dalrymple, G. Brent. 2001. The age of the Earth in the twentieth century: a problem (mostly) solved. Geological Society, London, Special Publications 2001, v. 190, p. 205-221. Click Here.

Dalrymple, G. Brent. 2006. How Old is the Earth: A Response to “Scientific” Creationism. The TalkOrigins Archive. Click Here.

Norman, M. D., Borg, L. E., Nyquist, L. E., and Bogard, D. D. (2003) Chronology, geochemistry, and petrology of a ferroan noritic anorthosite clast from Descartes breccia 67215: Clues to the age, origin, structure, and impact history of the lunar crust. Meteoritics and Planetary Science, vol 38, p. 645-661.

Stassen, Chris. 2005. The Age of the Earth. The TalkOrigins Archive. Click here.

Wikipedia, Teh. 2010. Age of the Earth. Click here.

So there you go.


  1. #1 See Nick Overlook
    November 19, 2012

    For someone like Rubio, the problem of the age of the Earth is complicated by the need to factor in the estimated number of voters who will be pissed off by his answer.

  2. #2 John Hentges
    San Diego
    November 19, 2012

    The senators comments were disingenuous but hardly incorrect!

    He merely said, if I may be allowed to paraphrase a bit, “I don’t want to answer “4.5 billion years” because my religious constituents would abandon me, but maybe they can be introduced to the truth if we frame it as seven ages that total to 4.5 billion instead of seven days…after all, who knows how long a gods’ day is in human terms?”

    We KNOW what the science answer is, we just have to allow the senator an attempt to keep peace with the ignorant, outdated bible thumpers in the wing of his party.

  3. #3 Kevin Sanders
    November 19, 2012

    Both John and SNO are correct. If my politician answers 4.5 bilions years, he will definitely lose my vote – especially if he says he is a Christian and still espouses the modern science belief in an old earth and evolution.

    Both of you are correct that the Republican base would abandon a candidate who believes in dribble drabble like that. He cetain would lose some of my support and all of it if a third party candidate with veiews similar to my own were running.

    If the Republicrats are smart and want our money to run their campaigns they know better than to go all liberal sciencey mish mash on us. We’ll pull their funding faster than lightening can strike a metal pole a mile high. They better either comply, or get fired. That simple.

  4. #4 Drivebyposter
    November 20, 2012

    Yes. Reality is a liberal conspiracy.

    Did you know pretty much all tech companies are liberal run?
    That’s probably a conspiracy too.
    Better abandon all electronics quick!

  5. #5 Eric Lund
    November 20, 2012

    Yes, Rubio has political reasons for not giving the scientifically correct answer. However, we are in “Opinions Differ Regarding Shape of Earth” territory here.

    Boasting of precision may not be the best tactical move here: Archbishop Ussher named a specific hour on a specific day in 4004 BC. If I’ve done the arithmetic right, that’s an uncertainty on the order of a part per billion. Of course, Abp. Ussher’s estimate is one of my favorite illustrations of the difference between precision and accuracy.

  6. #6 Nick Stuart
    November 21, 2012

    Rubio’s answer was essentially the same as one given by Barack Obama several years ago. Maybe someone can supply some links to the blogs and news reports taking him to task for it, I can’t seem to find any.

    If Rubio had answered 3.5 billion (which for some reason was the number stuck in my mind) he would be pilloried for muffing the answer. Nyah Nyah, Rubio was off by a billion years.

    Does anybody here posess epistimological certitude that in 20 years we’ll be told that “The science on this is pretty darn good. It is [whatever number, but something significantly different than 4.54 years].”?

  7. #7 Greg Laden
    November 21, 2012

    Yes, that certitude is pretty much in place! It isn’t the case that all scientific facts remain equally uncertain for their lifespan. They generally get more and more certain over time. The estimate of the age of the earth is not going to change much at all; at this point it is a matter of definition not dating: Do you want to “date” the earth at the first point where the mass of stuff roughly equals the current Earth + Moon, or do you want it to be when it reaches a fiery melty bally thing, or do you want it to be when you can stand on it and have your feet be only uncomfortably warm?

  8. #8 mark
    Piedmont Plateau Province
    November 21, 2012

    Rubio has a history of favoring Creationism, and is very wrong on his claim that there are other, equally valid age estimates, specifically of about 6,000 years. He is promoting anti-science and ignorance, hardly something that a member of the senate science committee should be doing. I have to agree with paul Krugman, who says if a policymaker believes in the magic of Creationism, we might expect him to believe in magical economic faiths such as “trickle-down” and the “confidence fairy.”

  9. #9 Matt G
    December 13, 2012

    What a goofy post. Why are people asking politicians science questions? It’s as though this post is trying to have a ‘gotcha’ moment with Rubio and there is nothing here.

    If you wanted to write about how old the earth is, just do it. You know need to include a politicians comments on it.

  10. #10 Greg Laden
    December 13, 2012

    Matt, actually, this post is all about how we know how old the Earth is. I just did it! The political reference makes a good point, the very same point you make in your comment.

  11. #11 Joseph
    January 14, 2013

    I feel that it is important to point out that the Bible does not make the claim that the earth is 6,000 years old. It actually says that the earth is ancient in the extreme and existed long before God said, “Let there be light” coincidentally meaning that time/history did not begin at the point but somewhere long before that.

    Genesis 1:2

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  13. […] In 2012, Sen. Marco Rubio (R-Fla.) refused to take a position on the age of the planet Earth, saying, "I'm not a scientist, man." (Scientists have long estimated the planet's age as 4.54 billion years.) […]

  14. […] In 2012, Sen. Marco Rubio (R-Fla.) refused to take a position on the age of the planet Earth, saying, “I’m not a scientist, man.” (Scientists have long estimated the planet’s age as 4.54 billion years.) […]

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