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Guest Post: How Old is the Earth? Who Knows?

The views expressed are those of the author and are not necessarily those of Scientific American.


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I’ve been away for the past two weeks at a truly fantastic conference — more on that in a future post — but promptly came down with a bad cold once we got home. Sigh. It’s hard to blog coherently with a stuffy nose, scratchy throat, and woozy brain. Fortunately, my pal Jim Kakalios, a physics professor at the University of Minnesota and all-around mensch, has come through with a guest blog post, inspired by recent comments on the campaign trail by would-be presidential candidate Rick Perry.

It’s especially timely in light of the just-concluded GOP candidates debate, in which the anti-science theme was particularly pronounced. I think anyone with a genuine love and respect for science and all the benefits to society it brings — regardless of political ideology — should be concerned by this ever-more-pronounced streak in the Grand Old Party. But here — I’ll let Jim explain how we know what we know when it comes to science, and why it’s so important for a civilized society to value fact-based, curiosity-driven scientific inquiry. Take it away, Jim!

* * * * *

Texas Governor Rick Perry, a candidate for the Republican nomination for President, was recently asked on the campaign trail how old he thought the Earth was.  He responded “I’m not sure anyone knows really completely know how old it is.”  While technically true – scientific measurements are continually being refined, allowing for more accurate determinations of the Earth’s age – it was an evasive response.

I suppose one cannot fault Gov. Perry for trying to weasel out of a direct answer – he is a politician after all.  As a scientist, in order to get a more productive response, I would have phrased the question slightly differently.

I would have asked Gov. Perry: “Which do you think is closer to the true age of the Earth – 4.5 billion years or six thousand years?”  And I have a follow up.

If he responded that the Earth’s age is closer to 4.5 billion years, I would then ask – why do you think so?

If he cites the overwhelming consensus of the scientific community on this age, then I wonder why he does not find equally convincing similar agreement among scientists on climate change or the theory of evolution.  A paper last year in the Proceedings of the National Academy of Science found that over 97 percent of climate scientists surveyed agree that global warming is a real phenomenon and that man made causes contribute to this warming.  This is not a sign of collusion – trust me, there is nothing scientists love more than showing that their colleagues are wrong.  If all but a small handful of scientists agree with a particular conclusion, it is because that is what the evidence indicates. Why agree with a scientifically derived age of the Earth, and ignore the scientific evidence for climate change?

If he replied that six thousand years is closer to the true age of the Earth, I would then ask – what about cell phones?

The scientifically determined age of the Earth is not just pulled out of a hat.  It is based upon measurements of the concentration of unstable uranium and thorium nuclei in rocks and meteors, employing a technique similar to Carbon-14 dating.  Extracting a time since the rock’s formation from these measurements requires an understanding of quantum mechanics, the field of physics that describes the behavior of atoms and nuclei.  There has been continual improvement, since the development of the first atomic bomb in 1945, in our understanding of the mechanics of radioactive decay of nuclei, with a corresponding decrease in the uncertainty of the age of the Earth, derived from such measurements.

Additionally, quantum mechanics, when combined with statistical mechanics, provides the foundation for solid-state and semiconductor physics. Modern quantum mechanics was developed in the mid-1920’s, and the transistor and laser followed approximately a generation later.  There would be no computer hard drives, magnetic resonance imaging, light emitting diodes, cell phones, laptop computers or iPods without quantum mechanics.

It is of course every American’s right to dismiss the conclusions of any body of science they wish.  But intellectual consistency would then suggest that one would mis-trust any electronic device that makes use of this science.  At least the Amish walk the walk, and don’t just talk the talk.

Why does it matter whether Gov. Perry, or any candidate for elected office, from either party, thinks the Earth is billions or thousands of years old?  Because science is not a collection of facts, but rather a process for how we can obtain reliable information about the natural world.  I would bet cash money that most scientists whose field does not directly involve radioactive dating of meteors are not familiar with the isotope decay curves from which the age of the Earth is determined.  But the process, by which evidence is obtained and then tested, challenged and ultimately accepted as correct, gives one confidence that when those who devote their research to such topics conclude that the Earth is 4.5 billion years old, the result can be trusted.

The scientific process has extended our lifespans, eradicated diseases, fed billions and as pointed out on an episode of the CBS comedy The Big Bang Theory last year, only sixty years after the Wright brothers flew at Kitty Hawk, enabled men to walk on the moon.  As citizens and voters we should discover whether our candidates believe that science is just another opinion, and then on Election Day, we can share our opinion of them.

James Kakalios is the Taylor Distinguished Professor in the School of Physics and Astronomy at the University of Minnesota, and the author of The Physics of Superheroes and The Amazing Story of Quantum Mechanics (Gotham, 2010).


Jennifer Ouellette About the Author: Jennifer Ouellette is a science writer who loves to indulge her inner geek by finding quirky connections between physics, popular culture, and the world at large. Follow on Twitter @JenLucPiquant.

The views expressed are those of the author and are not necessarily those of Scientific American.





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  1. 1. ben.bubnick 9:40 am 09/8/2011

    Unscrupulous!
    http://www.youtube.com/watch?v=Ok7mSB5pZc8

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  2. 2. boblsturm 12:56 am 09/9/2011

    “At least the Amish walk the walk, and don’t just talk the talk.”

    Actually, I was just in North East PA and was surprised to see a large number of Amish ladies at the Walmart buying disposable diapers, 2 liter bottles of Coke, and Cheetos. They were also accepting rides in cars.

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  3. 3. qatharms 4:26 pm 09/9/2011

    It is precisely my respect for the scientific process that makes me skeptical of claims for human impact in global warming. To date, I have not seen real evidence that implicates humans in changes in our global temperature. In fact, I am still waiting for a definitive explanation of the term “global temperature.” What I have read about that term so far gives me no confidence in either the definition or the measurements used to calculate it.
    Beyond that, there is plenty of evidence that massive changes in global temperature have occurred when there was no possibility of human influence. I don’t doubt that climate change happens. I don’t doubt that the global temperature could be rising. I do doubt that we know what the global temperature is and I do doubt that we can prove humans have anything to do with either the rise or the fall of a global temperature. I am open to real information on the subject. Bring it on.

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  4. 4. qatharms 4:29 pm 09/9/2011

    Oh, and for the record, I am deeply committed to God’s revelation of himself in the biblical record, but I completely believe that nature and the fossil record are real, not fake. I don’t believe that the God of the Bible plays mind games with human beings. I don’t think it is critical to my faith in God that the world be only 6000 years old. I recognize a real difference between the notion of the Bible as God’s revelation of himself to flawed human beings and the notion of the Bible as a scientific text.

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  5. 5. rwsimms 8:57 pm 09/9/2011

    Wow!… Just an observation, but I am also a scientist, and Jennifer Ouellette’s readers should know that there have been innumerable cycles in the past few hundred thousand years just like the one we are entering now. The fine line that people are stumbling over is that this time, during the time of a mechanized human race, man has inserted an effect on this one particular cycle. Because this is a matter of degree, everyone, scientists, politicians, (and the news media) can amplify or diminish this fact to their hearts content to benefit their own situation. In my opinion, it’s very small. It’s not a matter of whether or not we are in another warming cycle. This is what scientists agree on. It’s to what degree our environmental consciences let us inflate, or deflate man’s participation in this geologically very common phenomenon!

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  6. 6. Qedlin 12:50 am 09/10/2011

    This article is absurd drivel. The Amish will gladly ride in your car, use your electricity, phone, whatever. They are a religious cult locked in time and desperately needing liberation, but not the kind that science offers, with the presumption, arrogance and hubris it breeds.
    Whoever thinks that if you agree with some conclusions of science you must accept them all is an idiot.
    As my 7th grade Civics teacher profoundly taught us “If a man forgets or does not believe that E=mc**2, it is of little consequence, but if he forgets or does not believe ‘all men are created equal’, it is of grave consequence.”
    While scientists would like everyone to think they have some corner on truth and wisdom and the highest ideals of humanity, the country’s founding was decidedly on much higher principles, namely Judeo-Christian truth and the mercy and truth of “the Creator.”
    I could care less what Rick Perry knows about science, rather what he knows about “the Creator,” the Constitution and the founding principles of this nation.

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  7. 7. Quinn the Eskimo 12:53 am 09/10/2011

    How old is the Earth?

    As old as the dirt. Maybe older.

    Okay, I’m sorry. I won’t do that again. Maybe.

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  8. 8. R.Blakely 6:05 am 09/10/2011

    The problem is that climate science itself is more religion than science. First, “the overwhelming consensus of the scientific community” is a religious belief, not a fact. Thousands of other scientists know that humans cannot cause global warming.
    Earth’s climate tends to be self-regulating because it reacts to oppose change. For example, hotter weather causes more clouds, which reflect sunlight. Global warming should cause more clouds and so less rain.
    When we have floods we should blame global cooling. Rising sea level proves that global cooling is in effect, since this happens as glaciers melt. They melt since less snow falls on them. Global warming would result in more snow on glaciers, and falling sea level.
    I think most climate scientists are not real scientists. For example, climate scientists ignore the “law” that systems react to oppose change. Real scientists (chemists) are familiar with this “law”.

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  9. 9. yiati 7:47 am 09/10/2011

    How can we know so much about God and so little about ourselves?

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  10. 10. jgrosay 10:57 am 09/10/2011

    The problems some may have when reading “The Earth is 6000 years old” as a fact in the Bible, have an easy approach: in another text in the Holy Book, some speaks to God saying: “A thousand years are like a day in front of Your eyes”. In this, as in physics, time is just relative. Salut +

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  11. 11. jgrosay 11:03 am 09/10/2011

    To Yiati: what we know about God comes from his loving revelations, however, it’s clearly said that “God’s ways are unscrutable”. Our own ways are many times unscrutable to ourselves because we will be afraid of our real desires and our real nature and condition. If you dig deep in your mind, you may find unexpected and very dangerous or extremely unpleasant things. Some say: “If you want to be happy as you say, don’t analize, boy, don’t analize”

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  12. 12. GAry 7 12:01 pm 09/10/2011

    The scientific method is the single most important technique humanity has developed to determine the validity of our knowledge of the universe we inhabit.

    It should be taught in schools from kindergarten thru college. Having a powerful, efficient brain does not preclude inaccurate thinking. Having a powerful, accurate method of determining truth could well allow even the least among us to think well but that methodology must be inculcated while the brain is still plastic enough that the method becomes a part of the brains basic operating system.

    Most people seem to be operating under the brains equivalent of MSDOS,,,

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  13. 13. ncc1701z 9:31 am 09/11/2011

    If Galileo were alive today, Republicans would issuing subpoenas for his emails in an effort to discredit him.
    And I suspect that R.Blakely (#8 above) would be leading the pack.

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  14. 14. texacalian 2:48 pm 09/11/2011

    Whenever I read a “blog” on the web, I take the attitude that it is probably slanted, biassed, or simply a lie – unless its contents strongly indicate otherwise and can be checked against other, independent and reliable (according to one’s own ideas about what is reliable) sources of information. Too many people have the tendency to believe what is written in a blog unless it is obviously and blatantly unreasonable, just as they tend to believe another person’s statements unless they have the same defect. A blog on the internet is no more to be inherently accepted or believed than is another, unknown person, and readers should always remember that they may well be reading lies or propaganda. This factor is not alleviated by the provision of quotes, links, or cites: one liar agreeing with another either verbally or in print is no better validation than a single blog or person lying with no supposed corroboration whatever. The presence of a blog on any Scientific American webpage is no more believable for its own sake than a blog on any other webpage.
    I am not a “religious nut”, as many supposedly “scientific” persons are wont to accuse commentors with whom they disagree. I am a retired physicist, teacher, and continuing scholar, and am not religious, atheistic, nor any other form of “true believer” in the sense portrayed in Eric Hoffer’s book of the same name. Unless definitional agreement is made by users and hearers previous to its usage, “science” is simply a seven-letter word.
    To provide at least one reference to the article above, Perry’s remark was quite factual and straight-forward. All else written about it was nothing more than the blogger’s personal opinions. P.S. I am NOT a Perry supporter, I consider myself a supporter of truth and reason, however we can best define and determine them. (Yes: way too much about “me”. Disclaimers seem needed.)

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  15. 15. ConinCalgary 11:59 pm 09/11/2011

    Has no one added the years since they first came up with earth’s age? By now, it should be 4,500,000,010, or 6020 or whatever. Time doesn’t stand still while you argue about it.

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  16. 16. Jim Kakalios 1:31 pm 09/12/2011

    R. Blakely (no. 8) – I consider climate scientists to be “real” scientists – as does the National Academy of Sciences. Of climate scientists, who devote their career to the study of this issue, there is agreement (at the 97-98 percent level) on the existence of climate warming and that human agency as at least one cause.

    And by the way, only systems with negative feedback react to oppose change. A positive feedback system will amplify any change.

    To “texacalian” (no. 14) – I would think that there are quite a few “factual and straight-forward” statements in my essay. That an article from last year in PNAS did find that over 97% of climate scientists believe climate warming is real. That radioactive isotope dating places the age of the Earth at 4.5 billion years, plus or minus (ConinCalgary – your point, while correct, is within the rounding error on the measurement), and of the value to our lives of the scientific method, to take just three examples. To dismiss these as “personal opinions” is not what I would expect from a “retired physicist, teacher and continuing scholar.”

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  17. 17. jaimehlers 10:20 am 09/13/2011

    How old is the Earth? Certainly longer than human recorded history, the 6,000 year figure so often cited by a certain category of religious believers. I don’t really understand how anyone can say with a straight face that the world did not exist for more than a handful of days before humans came to be.

    By the same token, I don’t see how people can seriously deny the effects of human behavior on the environment, including climate. Are we next to hear that diseases like dysentery had nothing to do with human sanitation? The only question here is the degree to which human behavior affects climate, not whether it happens at all. We do ourselves no favors by sticking our heads in the sand and trying to pretend that we bear no responsibility for the effects our behavior has on climate.

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  18. 18. mihrant 6:57 pm 09/15/2011

    “A paper last year in the Proceedings of the National Academy of Science found that over 97 percent of climate scientists surveyed agree that global warming is a real phenomenon and that man made causes contribute to this warming.”

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  19. 19. mihrant 7:20 pm 09/15/2011

    “A paper last year in the Proceedings of the National Academy of Science found that over 97 percent of climate scientists surveyed agree that global warming is a real phenomenon and that man made causes contribute to this warming.” To my mind this quote from the blog is virtually meaningless and unscientific. To make it scientific it must be quantified. For instance, is man’s contribution 1%, 10%, or 50%? I think even skeptics would agree that it could be between 0.1 and 2%. So if we spend 100 billion dollars eliminating man’s contribution, big deal, it would have no significant impact of global temperature. Historically, the temperature varies about 10 F from the coldest ice age temperatures to an interglacial period, such as the one we are currently in. This variation is not due to carbon dioxide, which historically lags temperature by 800 years. It is most likely due to the change in insolation at latitudes of 50 to 70 degrees N, due to astronomical changes in the earth’s orbit around the sun. Insolation change is what causes summer and winter temperatures to differ. It has a very powerful annual effect. It also has a much smaller, but still significant, effect over tens and hundreds of thousands of years. The insolation started to decrease about 5000 to 10000 years ago, but due to natural lags, it has not been felt yet. For the next 50,000 years insolation will be at its lowest level for the past 500,000 years. There is no question in my mind (non-climate scientist, PhD in electrical engineering) that our future points to another -10 F Ice Age.

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  20. 20. texacalian 10:50 pm 09/15/2011

    To “texacalian” (no. 14) – I would think that there are quite a few “factual and straight-forward” statements in my essay…….. To dismiss these as “personal opinions” is not what I would expect from a “retired physicist, teacher and continuing scholar.”
    ========================
    I am not concerned about your expectations, but I certainly would expect better reading skills from someone who presumes to blog on this Scientific American webpage. My “factual and straight-forward” comment and also the “opinions” reference were quite clearly directed to Perry’s statement and your interpretations regarding it. He was stating that he did not think that anyone knew completely what the age of the Earth is. That is his opinion, and unless you have evidence that he was lying about his own state of knowledge, it must be considered factual and straight-forward about his own state of knowledge. If you consider it ignorant of him not to know that, that is merely YOUR opinion, as it is your opinion that he was dodging the issue, which you did not establish with any evidence. Again, I am not defending Perry, as I hope that he does not get the Republican nomination. But when you blog for SciAm, it seems to me that you should be a lot more careful to identify what you consider to be fact and what evidence there is to support it as being fact. It also seems to me that a lot of commentors and also their readers have a great deal of difficulty discerning the difference between evidence-supported facts and their own personal opinions. Quite obviously, too many of them do not even make any effort to so distinguish.

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  21. 21. semitope 12:30 pm 10/1/2011

    You are wrong. Scientists don’t enjoy proving each other wrong on major issues. When it comes to those, they are afraid of losing their position, grants, or being ridiculed. Issues like evolution, age of the earth, climate change etc are things that people are careful to take a side on. Take the example of evolution, where anyone who even things twice about it or suggests looking critically (being scientific) about it is instantly labelled and cast aside. People lose jobs over it. That statement is simply massively wrong.

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  22. 22. semitope 12:31 pm 10/1/2011

    Scientific consensus is barely useful in too many cases.

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