A1.2. Henry Eyring: The Age of the Earth

The Age of the Earth

Some words of wisdom from one of Mormondom's most prestigious modern scientists (Dr. Eyring was president of the American Association for the Advancement of Science and an accomplished chemist. The AAAS, incidentally, publishes "Science," which, along with "Nature" is the world's pre-eminent general peer-reviewed science journal). Note his concluding warning not to presume to judge the details of *how* God did things as being "fundamental" to our understanding of the Gospel as some literalists tend to want to do. - Marc

(an essay from Eyring, Henry. Reflections of a Scientist (SLC: Deseret, 1983; reprinted 1998): 53-57. My explanations and comments in square brackets)

When President Joseph Fielding Smith's book "Man, His Origin and Destiny" was published, someone urged it as an institute course. One of the institute teachers came to me and said: "If we have to follow it exactly, we will lose some of the young people." I said, "I don't think you need to worry." I thought it was a good idea to get this problem out in public, so the next time I went to Sunday School General Board meeting, I got up and bore my testimony that the evidence was strongly in the direction that the world was four or five billion years old. That week, President Smith called and asked me to come see him. We talked for about an hour, and he explained his views to me. I said, "Brother Smith, I have read your books and know your point of view, and I understand that is how it looks to you. It just looks a little different to me." He said as we ended, "Well, Brother Eyring, I would like to have you come in and let me talk with you sometime when you are not quite so excited." As far as I could see, we parted on the best of terms.

I would say that I sustained President Smith as my Church leader one hundred percent. I think he was a great man. He had a different background and training on this issue. Maybe he was right. I think he was right on most things, and if you followed him, he would get you into the celestial kingdom.


The scriptures record God's dealing with his children back to a "beginning" some six thousand years ago, but dismiss the long prologue in a few short paragraphs. The scriptures tell us of six creative periods followed by a period of rest. During these periods the earth was organized and took essentially its present form. In the King James Version of the Bible, the phrase "creative periods" is rendered as "days." The use of this term has led to at least three interpretations. In the first, the "days" are construed to mean the usual day of twenty-four hours. In the second, the days of creation are interpreted as thousand-year periods following such statements as occur in 2 Peter 3:8: "One day is with the Lord as a thousand years, and a thousand years as one day." The third interpretation accepts "creative periods" as times of unspecified length and looks to a study of the earth itself to give added meaning to the exceedingly brief scriptural accounts.

In earlier times some variation of the first two interpretations was all but universally held by the Christian world. This is no longer true. In school and in secular publications, the third interpretation is the generally accepted one. Accordingly, whatever our own point of view may be, we need to know the viewpoint presented to our children if we are to be effective counsellors to them.

The cumulative thickness of rocks laid down as sediment is about four hundred fifty thousand feet [128 000 m] or about 80 miles [130 km]. The rate of deposition varies enormously with the time and the place, but a not unreasonable average rate is one foot [30 cm] every 250 years. This leads to a very rough estimate of 112 million years for the time required to deposit all the known sediments.

Also, in my opinion, the orderly structure of these horizontally lying layers, with their fossils, argues strongly against the notion that the earth has been assembled, relatively recently, from the wreckage of earlier worlds.

A quantitative way of getting at the age of strata and other earth structures is by use of the radioactive decay of various elements. An analogy of how radioactive decay works may be helpful. If one should look at a fire and note that half the wood is burned the first hour and that an hour after that, half of what was left had burned, he could say the fire obeys the radioactive decay law. This law states that in a given length of time the same fraction of the fuel is burned, independent of the circumstances. Conversely, by measuring the fuel remaining as a fire and the amount of ashes already produced, one can deduce the fraction of the fuel consumed and so estimate how long the fire has been burning.

All the radioactive elements behave like our hypothetical fire in that, independent of the existing conditions, the same fraction of the radioactive elements is always transformed to another element in a given interval of time. The new element is the ashes of the radioactive fire; for example, half of the potassium (atomic weight forty) present to begin with changes into argon forty in a period of 1,300 million years, and half of what remains is changed in the next 1,300 million years, and so on. This period of 1,300 million years is called the half-life of potassium forty.

When a potassium-containing mineral crystallizes, it is ordinarily free of all gaseous argon. As time goes on, the potassium forty changes to argon forty at a rate determined by its half-life. If the crystal doesn't leak so that the liberated argon is retained inside the crystal, one can melt the crystal, measure the amount of potassium and the amount of argon, and so determine the age of the crystal.

If equal amounts of argon forty and potassium forty are found, the crystallization occurred 1,300 million years ago. If there is only one part potassium to three parts argon, 2,600 million years have elapsed since crystallization of the mineral occurred, and so on. Clearly, any potassium-containing mineral constitutes a built-in clock that we can use to read the time of the formation of the crystalline mineral.

Many complications may arise to make the clock give incorrect time. If some argon was entrapped in the crystal as it formed, the clock will read too long a time. If some of the argon has escaped since crystallization occurred, the indicated time will be too short. Nonetheless, by being careful to choose elements with appropriate half-lives and by careful selection of the crystal used and by sing more than one kind of a "clock," a reasonably consistent time scale for the formation of the various strata in the world has been achieved.

The radioactive clocks, together with the orderly way many sediments containing fossils are laid down, result in agreement by most scientists on an age for the earth of about four-and-one-half billion years. On the other hand, the exact age of the earth is apparently of so little import religiously that the scriptures sketch earth history in only the briefest terms. The present heated religious controversies on the subject will undoubtedly be resolved in time and will then appear as quaint as the mediaeval arguments on the shape of the earth seem to us now.

In my judgment, anyone who denies the orderly deposition of sediments with their built-in radioactive clocks places himself in a scientifically untenable position. Actually, the antiquity of the earth was no problem for two of our greatest Latter-day Saint leaders and scientists, John A. Widtsoe and James E. Talmage. However, there are vast differences in the training and background of members of the Church. Therefore, I am completely content that there is room in the Church for people who think that the periods of creation were twenty-four hours, one thousand years, or millions of years. I think it is fine to discuss these questions and for each individual to try to convert others to what he thinks he is right. It is only fair to warn parents and teachers that a young person is going to face a very substantial body of scientific evidence supporting the earth's age as millions of years, and that a young person might "throw the baby out with the bath" unless allowed to seek the truth, from whatever source, without prejudice.

The Lord made the world in some wonderful way that I can at best only dimly comprehend. It seems to me sacrilegious to presume that I can really understand him and know just how he did it. He can only tell me in figurative speech that I dimly understand, but that I expect to more completely comprehend in the eternities to come. He created the world, and my faith does not hinge on the detailed procedures he used.