How Old Is the Earth? How Can We Even Know?

“I wonder why, I wonder why.
   I wonder why I wonder.
      I wonder why I wonder why I wonder why I wonder!”

The lines above were penned by Richard Feynman while he was a student, before becoming one of the most famous physicists of the 20^th century. Not only was he curious about nearly everything; he was even curious about his own curiosity.

I remember the saying that "curiosity killed the cat." I am also aware that dogs, monkeys, apes, birds, octopuses, and many other animals appear to demonstrate a great deal of curiosity. But I doubt that any non-human animal on earth ever wondered about many of the things we wonder about.

Among other things, many of us tend to wonder how life on earth came to be, why we are here, and what (if anything) is the purpose of life. Some of us wonder about such things as the age of the earth and the universe. A few of us seem to wonder about nearly everything that crosses our minds. The intensity of our curiosity may be one of the distinguishing features of our species.

Until fairly recently, there were no answers to many of these questions except from philosophy or religion. Most people turned to religion. In the past two or three centuries, though, serious efforts have been made to answer some of these questions through scientific evidence. We still don’t have all the answers, but we’re getting some of them.

In this article, we’ll discuss efforts that have been made to determine how old our planet is and eventually reach a pretty firm conclusion. Like other articles on this site, this is a brief, simple overview. It is not intended to be all-inclusive or highly detailed. Rather, it is intended to help the average person like ourselves to understand the principles involved. I'll provide a few links to further details for those who want them.

The Age of the Earth According to the Bible

In the West, religion usually means Judeo-Christianity. Christianity is assumed to be based on the Bible; and Judaism, largely on the Torah. This discussion is simplified by the fact that “Torah” is simply a Hebrew name for the first five “books” of the Bible. Since this is where most of the “information” exists, we have only one place to go for most of it.

Christian Answers at http://www.christiananswers.net/q-eden/edn-c026.html tells us that “For thousands of years, a literal, straightforward, common-sense reading of Genesis and the rest of Scripture has led millions of intelligent Christians and Jews to believe that: (a) the universe was created in six literal days, (b) the Earth is only thousands of years old, …”

The guy who wrote that evidently still believes it! So do many others. But, as Anatole France said, “If 50 million people believe a foolish thing, it is still a foolish thing.”

Until fairly recently, nearly all Westerners believed the age of the world and the universe was a few thousand years. Not tens of thousands or millions or billions. The reason for this was people’s belief that the Bible was the literal “Word of God,” so whatever it said must be true and accurate. I’ve already dealt with that idea in other articles, and plan to deal with it further as time permits. (See Contradictions in the Bible, for example.)

Even now, the scientifically minded are sometimes ridiculed for mentioning billions of years. Or billions of anything!  (“There you go again with your billions and billions.”)

As is well known, the Bible contains several tedious genealogical lists, sometimes referred to as “the begats.” These are lists of male names that say essentially This-Man begat Somebody who begat Somebody-Else who begat Another-Guy who begat Still-One-More, etc. I think you probably get the idea. Some of these lists contain the ages of the father when he “begat” his son.

In case you haven’t figured out the archaic word yet, “begat” simply means “fathered” in these passages. It is actually a gender-neutral word that can also refer to the mother, meaning something like "bore" or "gave birth to." Either way, it refers to the birth of a child by its parents. Present tense is beget.

In principle, we should be able to add up the ages of fathers when their sons are born, or "begotten," to get a good estimate of lengths of time between events. See Genesis chapters 5 and 6 for examples. Another list begins in chapter 10, and there are still others in the Old Testament. Some of these lists, as well as the similar ones in the New Testament, don’t show ages and therefore are not significant for this purpose.

The fifth chapter of Genesis, verses 3 through 9, inform us, for example:

3 And Adam lived an hundred and thirty years, and begat a son in his own likeness, and after his image; and called his name Seth:

4 And the days of Adam after he had begotten Seth were eight hundred years: and he begat sons and daughters:

5 And all the days that Adam lived were nine hundred and thirty years: and he died.

6 And Seth lived an hundred and five years, and begat Enos:

7 And Seth lived after he begat Enos eight hundred and seven years, and begat sons and daughters:

8 And all the days of Seth were nine hundred and twelve years: and he died.”  

9 And Enos lived ninety years, and begat Cainan:

You can see there's more information here than we need for our purposes, so let me specifically point it out. We've already been told (Genesis 1:26-31) that God created Adam. Now we learn in verse 3 that Adam was 130 years old when his son Seth was born. Seth was not the first son of Adam and Eve; remember Cain and Able? (You'll find their story in chapter 4.) But that's OK; Seth is the one who is important to this discussion, since we know when he was born -- 130 years after the creation of Adam.

Verse 6 tells us that Seth was 105 when his son,  Enos, was born. That's 235 years after the creation (130 + 105 = 235). According to verse 9, Enos was 90 when his son, Cainan, was born; so we're up to 325 years after the creation now (130 + 105 + 90 = 325). If we continue this way, we can calculate that Noah was born about 1056 years after the creation, and the worldwide flood would have been 1656 years after it, when Noah was 600 years old.

Noah was a 500-year-old stud when the first of his three well-known sons -- Shem, Ham, and Japheth -- was born (Genesis 5:32).

Anyway, the lists continue for almost 4,000 years. if one ignores the absurd ages given (as people have ignored them for thousands of years) and simply adds them together, the sum will be the supposed number of years since the creation of Adam, the world, and the universe. By that time, we can correlate them with historical events to determine how long ago they happened.

While there is considerable disagreement among the "believers," we can theoretically calculate about how long it's supposed to have been from Creation Day to the present. Then we should know the age of the earth, as well as the maximum age of everything else in the physical universe.

EadsHome Ministries at http://www.eadshome.com/ relates them (as of the time this article was originally written) to the call to rebuild Jerusalem (444 BC), the birth of Christ (6 BC), and the death of Herod the Great (4 BC). The dates are theirs; not mine. Dr. Eads concludes that Adam was created sometime around 4174 BC. Since the Bible clearly says Adam was created on the sixth day (just five days after “God created the heaven and the earth”), then it follows the earth and the entire universe are now (in 2007 AD) about 6,181 years old.

Catholic Archbishop Usher in Ireland in 1654 did similar calculations and decided the creation of Adam was at 9:00 am on October 26, 4004 BC. I did similar calculations several decades ago and came up with the same year, but I have no idea how Usher arrived at a date and time. Usher's calculations -- as well as my own -- would indicate everything is about 6011 years old now.

Others over the centuries have come up with dates from about 3400 BC to almost 7000 BC for the Creation. I don’t know where the differences came from. Maybe different translations of the Bible or different interpretations of the timing of historical events. It doesn’t really matter any more. During the past century, an overwhelming mass of scientific evidence has accumulated that the earth is vastly older than any of those estimates. Hundreds of thousands of times older!

Even some who still claim the Bible is “God’s Word” are looking for loopholes. Possibly the most common argument -- among several others -- is that there might have been any amount of time (“possibly even millions of years”) between Genesis 1:1 when “God created the heaven and the earth” and Genesis 1:2 when “the earth was without form, and void.” This possibility is still denied vociferously by others.

As of July 25, 2005, the home page of Missouri Association for Creation, Inc., at http://www.gennet.org/, states honestly, “Most of us would like to believe that we bring a completely open and unbiased mind to the issue of origins. We prefer to think that we harbor no unprovable starting assumptions, and that we would not hesitate to abandon even our most fundamental beliefs about origins if the facts were to require it. There may be certain individuals and even certain fields of science where this blissful neutrality prevails but it is most unlikely when we deal with the question of our origins. Here the facts are too few and the philosophical stakes are too high.”

I agree completely. Many of us were taught things from infancy that are likely to prejudice our opinions. The approximate age of the earth, the solar system, and the universe are important knowledge about our beginnings. If we would really like to know the truth -- whatever it is -- then we must examine the evidence with open minds, and this is very difficult for many of us. But let’s look at some other attempts to determine some of these ages, and see what they offer.

James Hutton and Uniformitarianism

James Hutton (1726-1797), now known as the Father of Geology, was born in Edinburgh, Scotland, on June 3, 1726. During his high school and university education there, he acquired a passion for scientific inquiry.

He was apprenticed to a lawyer, but later switched to medicine. After studying medicine in Edinburgh and Paris, he obtained his doctor’s degree at Leiden in 1749. Then he concluded belatedly there didn’t seem to be any need for another medical doctor, so he abandoned the medical profession.

For a while, he farmed some land he had inherited from his father; but he also spent time traveling in Holland, Belgium, and France. During his travels, he began to study the surface of the earth.

Apparently, he was never married. After about 1768, he lived in Edinburgh with his three sisters until his death in 1797, devoting himself to scientific research. In 1785, he published his Theory of the Earth.

Hutton was a very religious man, and (according to several different reports) was inclined to follow his religious beliefs as far as possible. Nevertheless, he studied what was known about the geology of the earth and learned for himself whatever else he could.

He saw, for example, that Hadrian's Wall, built by Romans about 1,500 years earlier, showed very little deterioration. Since the earth itself showed great signs of wear, he suspected the planet was much older than the few thousand years calculated by Usher and others.

He realized that very slow processes shape the earth. Mountains arise continuously, only to be eroded by weather and living things. Eventually, he developed the principle of uniformitarianism, which said "The present is key to the past." He believed the physical and chemical laws that govern nature have been uniform throughout the past and would be equally uniform throughout the future. Therefore, he said he could see "no vestige of a beginning, no prospect of an end" to the earth.

In his opinion, the earth was eternal. It had no beginning and would never end.

Actually, uniformitarianism is a reasonably accurate representation of reality over long periods of time; but not for eternity. Over a long enough period of time, it is punctuated occasionally by massive vulcanism on a scale Hutton probably never imagined, asteroid strikes and possibly other extraterrestrial events, and more. Maybe more to the point, when radioactive decay of certain materials was discovered about the beginning of the 20^th century, it was realized that earth could not possibly have existed forever in its present form.

Uniformitarianism was largely discredited by the end of the 18th century.

Lord Kelvin and the Cooling Rate

By the mid-nineteenth century, Joseph Fourier had developed a theory of heat conduction. The British scientist, William Thomson, later and more commonly known as Lord Kelvin, used Fourier's equations to calculate the minimum age of the earth.

He knew the earth's temperature increased about one degree Fahrenheit for each 50 feet you dig into the ground, at least near the surface; and he guessed that the earth began as molten rock about 7000° F. By solving Fourier's equations as they related to temperature change, Kelvin found that it must have taken about 98 million years for the earth's temperature to level out to its current value of about one degree for every 50 feet.

This method involved a considerable amount of guesswork. For one thing, he could know for certain that the entire world had ever been molten. If it were, then he could estimate the minimum temperature it must have been; but he could not know how much hotter it might have been. Because of ignorance of these and other variables, he knew his calculation could not be accurate. Nevertheless, his reasoning was ingenious.

To allow for the ignorance inherent in his variables, he concluded that the earth could not have been less than 20 million years old, but might have been as much as 400 million.

One thing Kelvin still didn’t know about was radioactivity. He had no way to realize earth has its own internal source of heat that keeps it from cooling off at the calculated rate. Radioactivity in the earth makes it cool more slowly; without it, Kelvin's calculations would have made sense. But because of the heat produced by radioactive decay, his method was useless for even estimating an upper limit on the age of the earth. It did, however, set a new minimum age range.

Therefore, he had correctly concluded the earth was at least 10 to 20 thousand times older than the age based on Biblical references. Now we know it’s even older still.

Charles Darwin and Erosion

In 1859, Charles Darwin, in the first edition of On The Origin of the Species by Natural Selection, made a crude calculation of the minimum age of the earth by estimating how long it would take erosion occurring at the current observed rate to wash away the Weald, a great valley that stretches across southern England between the North and South Downs. He obtained a number for the "denudation of the Weald'' in the range of 300 million years, which he concluded was long enough for natural selection to have produced the astounding range of species that exist on earth.

Sedimentation Rates

Others studied sedimentation rates and the thickness of sedimentary rock at various places to determine how long it would have taken to deposit the rock layers. There was a great deal of variability from place to place, of course, which led to widely varying estimates of time. Equally important is the fact that plate tectonics were unknown until the mid-twentieth century. Plate tectonics destroy parts of the earth's surface continually, so that the last square meter of the original surface was most likely destroyed long ago.

These people were unknowingly studying layers that may have been laid down millions or billions of years after previous layers had been destroyed. Again, they were able to establish new minimum ages for the earth; but it was impossible for them to establish a maximum age.

John Joly and the Salt in the Ocean

In 1899 - 1901, the Irish scientist, John Joly, estimated the rate of delivery of salt to the ocean. River water has only a small concentration of salts. As they flow to the sea, evaporation concentrates the salts; so he hypothesized that the ocean was constantly getting saltier. It made sense.

He figured the age of the ocean equals the total amount of salt in the oceans divided by the amount of salt added to the oceans per year by all the rivers. The math could not have been simpler. He said the earth must be 90 to 100 million years old.

The most obvious problem with this is the impossibility of actually collecting the necessary information from all the rivers in the world. Another was that he had no knowledge about whether or how fast salt was being removed from the sea-water.

We know now that salt is being removed from the oceans by several different processes, and most of the ocean is in approximate equilibrium between salt and water; so these calculations again could -- at best -- only produce a minimum age, and even that was based on some incorrect guesses.

Charles Lyell and Evolutionary Time

During the latter 1800s, Charles Lyell compared the amount of evolution shown by marine mollusks in the various series of the Tertiary System with the amount that had occurred since the beginning of the Pleistocene. Without modern DNA information, he must have used some pretty crude estimates of how much evolution had occurred. Regardless, he estimated the Cenozoic period alone lasted 80 million years.

Rutherford, Boltwood, and Radioactive Decay

In 1896, Henri Becquerel stored some uranium crystals in a desk drawer next to some photographic plates wrapped in dark paper. For some reason, he developed the plates even though they had not been exposed, and was amazed to find images of his uranium crystals on them. He had discovered natural radioactivity purely by accident. (X-rays had been discovered the year before.)

By 1905, it was understood these natural rays were produced by the decomposition of uranium into helium. By making certain assumptions based on the best information at the time, Rutherford and Boltwood used this understanding to calculate the age of various rocks and minerals containing uranium. Some were shown to be as much as 500 million years old.

By 1907, Boltwood suspected correctly that lead was the stable end product of the decay of uranium and published the age of a sample of urananite based on the more accurate Uranium-Lead dating. Its calculated age was 1.64 billion years.

Many radioactive elements can now be used as "geologic clocks," to calculate the age of minerals in which they are found. Each radioactive element decays at its own constant rate, referred to as a half-life. Once this half-life is known, geologists can estimate the length of time over which decay has been occurring by measuring the amount of radioactive parent element and the amount of stable daughter elements.

Virtually everything on earth contains radioactive materials and can -- in principle -- be dated with these and related methods. There are many different variations, and sometimes there are advantages to using one method over another. Or one radioactive material over another.

Some methods have special requirements. For example, using some methods, we must be able to determine how much of the radioactive element and its stable daughter was in the rock or other sample when it was formed. Other methods either give accurate answers even when this is not known, or else a test included in the method signals an incorrect answer so we will know not to depend on it.

Some methods are generally more accurate than others for a variety of reasons, and we’ve had a century now to find the best methods and to learn when to use each one. For that reason, radioactive dating now is generally very accurate. In most cases, several methods are used on the same item; and the results should agree with each other. Normally, they do agree, and this agreement among different methods provides a great deal of confidence. In cases where they disagree, obviously, we still don't know the answers until we can figure out why and what to do about it.

There is no particular reason to think we have found -- or will ever find -- earth rocks as old as the planet itself. Not only do the actions of weather and living things decompose and bury rocks, but tectonic action is even worse. A continental plate subducting under another may take parts of the earth’s surface miles deep into the interior. During the past four billion years, nearly all the world’s surface has been destroyed this way. The surface we walk on was mostly formed by this recycling action long after the earth itself.

A four billion-year-old rock would be one that has escaped tectonic action as well as erosion for that many years. It’s surprising that we ever find a rock anywhere near that age on earth. Therefore, the oldest rocks we find that originated on earth can still only set a minimum age for the planet.

When I first wrote this article several years ago, the oldest known rocks (excluding meteorites that originated elsewhere in the solar system) were about 3.8 billion years old. Even then, it had already become clear that earth was formed with he rest of the solar system; and various scientists had shown the solar system to be at least about 4.55 billion years old. Since that time, a few older rocks have been discovered, pushing the minimum age of earth consierably closer to that figure.

Certain rocks called "faux amphibolites," found in a formation called the Acasta Gneiss in Canada's Northwest Territories, have been dated at 4.03 billion years. Exposed bedrock on the eastern shore of Hudson Bay in northern Quebec, has been shown to contain samples from  ancient volcanic deposits as old as 4.28 billion years. And tiny zircon grains in Western Australia have been dated at 4.36 billion years old. So far, these are the oldest samples of our planet that have been found. Indeed, there may be none any older that still exist.

Once again -- though with far greater precision and confidence than ever before -- we have only succeeded in determining by the rocks that the world is at least a certain age: 4.36 billion years. This still doesn’t tell us how much older it might be, which is why we had to go beyond the earth into the solar system for a probable maximum age.

Now, with the Hubble and other ultra-sensitive telescopes, we have begun to actually watch other star systems in various stages of formation. By observing many different systems in different stages, we verify and refine our theories about the origin of our own system. Now we feel pretty confident about the 4.55 billion year age of earth and the rest of the solar system..

Conclusions

So what have we actually learned? We've learned that our planet, the sun, and the rest of the solar system formed about 4.55 billion years ago, with a potential error of plus or minus about one percent. New evidence is not likely to change this figure significantly in the future.

Claims to Be Aware Of

Some "believers" claim the laws of nature were changed by God in many different ways and at different times. There is no evidence that this ever happened. All known evidence indicates the basic laws of nature have remained the same since the Big Bang occurred around 13.7 billion years ago.

For more information, see the following websites

• Radiometric Dating, A Christian Perspective
  For many readers, this may be the most important link here. Dr. Wiens, the author of this 33-page document, refers to himself as a Christian who believes the Bible and has a PhD in Physics and a minor in Geology. His PhD thesis was on isotope ratios in meteorites, including surface exposure dating. He was employed at Caltech's Division of Geological & Planetary Sciences at the time of writing the first edition. He is presently employed in the Space & Atmospheric Sciences Group at the Los Alamos National Laboratory. He first wrote this in 1994 and updated it in 2002.

• Earth's Past Timeline

• The Age of the Earth

• US Geological Survey

• Dendrochronology
  Studying a 4,767-year-old tree and its neighbors that have been growing together for at least the past 9,000 years

• Astronomical Cycles
  How astronomical cycles tell us a particular rock is 25 million years old

• Radiometric Dating: Clair Patterson

• US Department of the Interior Geological Survey

There are many additional sources of reliable information on this subject.

This page was last updated 08/21/09 04:43 PM.

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