The age of the earth
Benjamin F. Plybon
Emeritus Professor of Mathematics, Miami University
How old is the Earth? How does one find an answer to that question? Intelligent people ask questions and then look for answers. As intelligence developed in our primitive ancestors the time came when someone asked that question about the earth. No one knows when that first intelligent human began to wonder about the age of the earth. At that time no one was able to determine the answer to that question. It is easier to ask questions than to answer the good questions but it requires intelligence to even ask a good, thought-provoking question. These are the questions that stimulate deep thinking, and eventually moves us a bit forward in our search for knowledge. This is such a question, motivation for much deep thought and research for centuries.
In ancient times, by 3000 BC, there were many traditions and speculations about that age. The ancient Israelites had their traditions about the beginning of all things but in their writings there was no numerical value given for the number of years since the creation. When thinking about such a numerical value we need to remember that those ancient thinkers were not yet aware of our modern ideas about years and time periods. For us today a year is the length of time required for the earth to complete one revolution about the Sun. Methuselah and Noah knew nothing about such things. Their understanding of year was different from ours. That is probably the reason why we read stories in the first eleven chapters of the book of Genesis in our Bible about people living hundreds of years, some over 900 years. Noah began building his Ark when he was 600 years and after the end of the Flood he lived another 350 years. Obviously those were not our years of length about 365 and1/4 days.
Some Christians today still believe the answer to the earth age question can be found in our Bible. In 1700, many Christians believed another wise Christian had found the answer to the age question. They believed a Bishop named Ussher had found the answer in the Biblical book of Genesis.
James Ussher, an Irish Archbishop published a Christian answer to the age question in 1658. He maintained that the first day of creation was Sunday, October 23, 4004 BC. He also concluded, Adam and Eve were ejected from the Garden of Eden on Monday, November 10, 4004 BC. Very few people today believe his conclusions were correct, and some may even regard them as foolish. But Bishop Ussher was no fool. This man was a respected scholar, Vice-Chancellor of Trinity College in Dublin, Ireland, and an expert on ancient history and the scriptures. His published work reveals a very intricate and scholarly study of material he used as a basis for his work. He did much more than simply add up the ages in the Old Testament genealogies as some critics suppose. Despite these facts, few if any educated people today, Christian or atheist, believe the Earth is only about 6000 years old.
By mid nineteenth century, geological studies had provided evidence indicating that the earth is much older than 6000 years. The geologist, Sir Charles Lyell, rejected Bishop Ussher’s age estimate and was one of the first to consider the possibility of determining the age using a scientific approach. Lyell wondered. Is there some way to use present day measurements and apply current scientific theories and mathematics to answer the age question? Many believed this was possible. It is curious, that Lyell himself did not make any attempt to estimate the age of the earth, but as a result of his work in geology he believed our planet to be very old, possibly many billions of years. Various attempts were made by other investigators in the following years.
All such work begins with some assumptions. Most early attempts began with a basic assumption known as the hour glass principle; find some process of change that has been going on since the earliest times and assume the rate of change is constant. From present values of the changing quantity and an estimate of the rate of change we can determine an estimate of how long the process has been going on. Lyell made the interesting claim that all geologic processes, such as erosion and deposition, have continued over the life time of the earth at a constant rate, so this provided a scientific base for application of the hour glass principle. Processes such as sedimentation of rocks, erosion, change in the salinity of sea water and various cooling processes were used. Best results were obtained from measurement of the temperature of the earth and calculation of the rate of cooling. The most famous of these efforts was the work done by the British physicist, Lord Kelvin, also known as Sir William Thomson.
Thomson graduated from Glasgow University at age 10, moved on to Cambridge and graduated at age 21, with honors. At age 22, he was a full professor of natural philosophy at Glasgow University. Thomson was a brilliant physicist and mathematician, and an expert on the physics of heat, so it is natural that he would try to use that expertise in his investigation of the age problem. Geologists at that time believed the earth originally had been a molten mass that cooled over time. Other investigators before Thomson had used this idea to make an estimate of the earth’s age from observations of present temperature and some assumptions about the rate of cooling. Isaac Newton and the natural philosopher Joseph Fourier had laid the foundations for this work many years before.
Thomson’s first estimate was made in 1862 and his calculations suggested an age between 100 and 200 million years. He continued to revise his calculations over the years and his age estimates fell to lower and lower numbers as he refined his calculations. His final estimate of 24 million years was made in 1897.
But at the end of the nineteenth century the geologists and evolutionists believed the age must be greater than 24 million years. They were sure the earth must be much older than that. In 1859, Charles Darwin published his work, The Origin of Species, which was immediately accepted by most naturalists as fact. However, in order to produce the observed species and explain the fossil record huge amounts of time, billions of years rather than millions of years, were required. In his text Darwin made no claim about the origin of life but he did attempt to explain how the great variety of life forms we see today arose by the process of natural selection from primitive, possibly microscopic life forms. This was a clear contradiction to the Genesis account if the Genesis account is read as a literal description of the creation of life on earth. Some Christians still do that but probably most today do not.
Bible scholars today believe the writings in the Biblical book of Genesis were based on centuries of oral traditions and various religious documents not available to us today. Fragments of these ancient documents have been identified by Biblical scholars, embedded in the scriptures we know today as Genesis, Exodus, Numbers, Leviticus, Deuteronomy, and Joshua. An unknown writer, sometime after 1000 BC, collected these traditions and writings and assembled them into a document that became the source for the material in the first six books of the Christian Bible. Bible scholars call this document the Hexateuch. Probably the writer’s purpose was to preserve these records for future generations of his people, the ancient Jews. His people needed to be reminded of the reason why they were called God’s chosen people. Although none of this material could be considered scientific knowledge, there are great truths about people, the world around us and God, contained in these writings. That is why they are valuable to Christians.
The first eleven chapters of Genesis are considered to be pre-history, in the sense that we can’t correlate any of the events described in these writings with current historical knowledge of the ancient world. We can’t locate the Garden of Eden or Noah’s Ark on the map today. We can’t place Noah’s birthday or the flood on a timeline based on our current calendar. However, beginning with Chapter 12 of Genesis we find mention of real places, locations known today, and events that correlate with current knowledge about the ancient middle eastern world. The people such as Abraham, Isaac and Jacob are believed to be real people. We can’t be sure about Noah or Methuselah, however.
There is no reason to believe the individual who collected this information and wrote it down had any interest in presenting a “scientific” account of the origin of the world. He was interested in theology and the history of his people, the Jews. He did want to explain the origin of the Jewish nation and remind his people of their relationship to God; why they believed as they did. There were good reasons for their beliefs. There was an interest in preserving their accumulated knowledge of God.
First of all, the God they worshiped was the creator of all things, including human beings and all living things. That is the primary truth in Genesis, Chapter one. The details given there provided the best description of the beginning of all things available at the time of the writing. In that sense it is similar to our present day scientific collection of facts and theories about the origin of all things. But the source was revelation and deep philosophical thinking by the ancient forefathers of the race, not scientific observation and analysis.
The Old Testament Jews made no known contributions to science or mathematics as we understand these subjects today. They didn’t ask scientific questions. Some authorities believe this was because they relied on God and the prophets to provide answers to their questions. The science of the ancients known to us today came primarily from the Babylonians and Egyptians and later from the Greek world, not from Israel. In later centuries contributions to science and mathematics came from India and the Arab world, but still no contribution from the Jewish world. This is interesting in view of the fact that the world of the Jews has produced some of our best scientists in the past 500 years. An outstanding example is Albert Einstein but there have been many others. It seems clear, that the author or authors of the Genesis creation story had no intention of providing a scientific answer to any scientific question.
Darwin’s theory was intended to provide a scientific explanation of the variety of life forms we see around us today. He did not merely sit in his parlor and speculate on the matter. That was the approach used by the scholastics in the middle ages. In the years shortly before and after 1600 AD the English philosopher, Sir Francis Bacon, attacked the scholastic style of discovering truth and demanded careful, meticulous observation of the natural world, followed by analysis and experimentation. The Baconian approach to scientific discovery became the foundation for scientific thinking in the 17th century, the age of Newton, Galileo, Robert Hooke and Edmund Halley and continued throughout following centuries.
Darwin followed in that line. He spent many years observing both plant and animal life in many parts of the world while traveling as a passenger on a sea voyage. The story of the voyage of the Beagle is well known to Biologists. After years of study and analysis of his observations he arrived at his theory of Natural Selection, which is the heart of the so-called theory of evolution. It is important to note the source of his explanation: he gathered data and followed up with careful analysis. That is why the theory of evolution is labeled as science while the Genesis account is not.
After Darwin published his theory, interest in the age question was renewed. If his theory was correct then the earth must be billions of years old. An earth age of a few thousand years would not suffice to explain the geological and biological evidence. A new scientific attack on the question of the age of the earth began. Sir William Thomson, one of the leading scientists of the time, made his analysis as noted previously. His final figure was 24 million years. But this seemed to be too short.
What happened next is an interesting example of how the world of science operates. Radioactivity was discovered by physicists, just prior to the end of the nineteenth century, at the very time geologists were struggling with the problem of determining the age of the earth. The timing was perfect. Physicists discovered decay of an isotope of an element such as Radium or Thorium proceeds in a very uniform fashion, obeying a precise physical law that can be expressed in mathematical form. This means if we are given a certain amount of Radium, such as one gram, at a certain time then we can calculate very precisely the amount of Radium left and the amount of the daughter product formed at the end of one year, 10 years, or even 10,000 years.
This was a perfect physical process to employ in application of the hour glass principle for estimation of the age of the earth. Many radioactive elements are known today. A precise measurable decay constant is associated with each of these elements and these numbers have been measured with great precision by physicists. Direct application of the physical law obeyed in decay processes seemed to be impossible because that would require accurate knowledge of the amount of a certain radioactive element present in a given sample at some time in the past. Knowledge of the precise amounts in the past is not available to us. But there are various ways known to geologists, chemists and physicists to make good estimates of the original amount of a given radioactive element in a rock or piece of wood at some time in the past. These are sufficient to show the earth is much, much older than a few thousand years. Techniques designed to measure the age of ancient materials using the physics of radioactive elements are known as radiometric dating methods.
The so-called carbon-dating process is an example of this kind of dating of ancient objects. There are biological reasons for believing that a tree, bone or plant must have had a certain amount of carbon isotope C14 in it at the time of death. At the time of death of the source of the organic material, C14 begins decaying to C12 , the stable isoptope. From measurement of the amount of C14 still present in a piece of wood or bone today it is a simple matter to estimate the age of the wood or bone fragment. Of course this is only a description of the basic idea for this dating method. The actual scientific dating process requires sophisticated techniques for making precise measurements and adjustments for possible sources of errors. After decades of study by thousands of researchers, scientists have developed carbon dating into a very precise technique for dating objects of interest to archeologists and anthropologists. However, the technique is useful only for objects less than about 25,000 years old at the present time. That is sufficient for dating bones and many objects made of organic materials but even 19th century estimates indicated that the earth is much older than that. A method applicable to longer time periods was needed.
Measurement of the age of the earth is done by measuring the age of rocks. It seems safe to assume if a rock is found to be about 3.8 billion years old then the earth must be at least 3.8 billion years old. A precise method for determining such ages was found. A very accurate radiometric technique known as isochron dating was discovered. This discovery is a beautiful example of the application of physics and mathematics to find a solution to a scientific problem. However, this is not the place to give a detailed description of the theory and techniques used to make such radiometric dating measurements. The important fact to know is that the isochron method has been used for decades now to determine ages of the oldest rocks and scientists have verified the accuracy. Most readers would not have the background in physics or mathematics to understand such a treatment. Numerous books and articles have been written on the subject, however, and the interested reader can find all of the details in available sources. A very readable technical account is given in the 1969 textbook, Physics of the Earth, by Frank D. Stacy. A less technical, but very good account, is given in the 2001 book, Mysteries of Terra Firma, by James Lawrence Powell. A Google search on the keywords “isochron” or “age of the earth” or “radiometric dating” will produce much Internet material on the subject for readers interested in details.
The essential fact is that in scientific circles researchers regard the earth-dating problem as a solved problem. There is no longer any mystery about the matter. The study of rock ages is being done by Geologists and Chemists every day and they will continue to do research on refinement of field techniques used to analyze samples of course. Samples will continue to be collected, gathering more age estimates. Age estimates of samples vary but at the present time all such estimates are consistent with an earth age of about 4.5 billion years. Analysis of meterorite samples and lunar rocks give similar age values.
So, scientists are convinced that the age of our earth is about 4.5 billion years. Yet some people among the so-called young-earth-creationists question the current accepted scientific values on the basis of various possible sources of error in sample measurements. They also question the physical assumption that decay constants for radioactive isotopes remain fixed in value over long periods of time, despite varying environmental conditions. These possible error sources and many other possible sources of error are of course well known to researchers who employ radiometric dating. These methods have been used for decades by thousands of highly skilled researchers who have refined their techniques to correct for some of the possible errors in sample measurements. Testing has produced no evidence to indicate decay constants change perceptibly over long time periods under any kind of conditions. So the conclusion must be that present estimates are very close to truth.
Unwise Christians, in their desire to defend their faith, do not want their children taught that the earth is billions of years old. I am a Christian and my four children were raised as Christians. They learned the earth is about 4.5 billion years old. That is a fact and Christians are firm believers in truth. This fact about the age of the earth is no threat to any Christian with a sound understanding of the Bible and the faith we profess. When your faith contradicts known facts about the world it is time to re-examine your faith. Before attacking the science teachers in your local school please show some respect for these people as educated professionals doing a necessary and valuable task. An essential fact to remember is that in teaching science students in a science class about this scientific problem one must present the best of what is accepted today by experts in this field. Otherwise it is not science that is being taught. Any other opinions, true or not, belong out side of the science class.
It is troubling that so many people believe teaching children in a science class the truth, that the earth is probably about 4.5 billion years old, is a denial of God and his Holy word, the Bible. But the Bible makes no statement about the age of the earth. In 1658 a brilliant man determined a Christian estimate of the age of the earth from Biblical information. We know today his estimate was incorrect. It is not likely anyone today could improve on the work of Bishop Ussher.
I am less certain about correctness of Darwin’s theory of Natural Selection as the explanation for the origin and development of life forms, but this is the accepted explanation in the scientific world. The theory is based on observational evidence and is consistent with other related science such as genetics. Clearly species have come and gone over long periods of time, and life forms have changed radically since the earth was formed. The evidence shows some form of evolution did occur. Darwin’s theory is the best explanation for the evidence scientific research has produced.
One feature of Darwin’s work I do applaud as good science. Good scientists seldom ever claim certainty about their theories. Quantum Mechanics is one of our most successful physical theories but even Einstein had doubts about Q mechanics and believed it would eventually be replaced by a better theory. Darwin notes in his first book on the subject that there are many problems and unanswered questions, and some of these are still with us. He did an honest evaluation of his thoughts. He realized that billions of years would be required to make his theory work. That was a problem for Darwin but not for biologists today. The age of the earth problem has been settled. Science knowledge also evolves over time. Present knowledge of genetics, an unknown science in 1860, has settled some of his questions about the mechanics of Natural Selection. But some unanswered questions remain. There is nothing wrong with that. Darwin was doing his job as a scientist when he included possible objections to his work.
On the other hand we have fundamentalist Christians who question the scientific claim about the age of the earth, claiming to represent all Christians, with their misinterpretations of the scriptures. They agree with Bishop Ussher and base this on their misunderstanding of Genesis. They call this faith in the Bible. A literal interpretation of the early chapters of the book of Genesis was acceptable to many in 1600, but should not be acceptable to thinking people today. That is a mistaken idea of faith in God. Learning the true age of the earth is an advance in our knowledge of God.
When reading the scriptures we should make an attempt to determine what the writer was trying to communicate to future readers. We are better equipped to do that today because of better understanding of the ancient world and it’s peoples. The author of the first chapter of Genesis lived in a very primitive world with little or no knowledge of the natural world in a scientific sense, so there is no reason why readers today should read these writings as science. The great truth expressed by the author is that the God in which he believed was the Creator of all things and God cared about his new creatures. The rest is a literary form adopted by this unknown writer.
I am told that in the original Hebrew, Chapter One of Genesis is beautiful poetry. That is true of much of the Old Testament scriptures. So the work should be read with that in mind. Poets choose words and expressions to create images and emotions in a way not possible with prose. The poet is not trying to communicate facts in a literal sense. All great poetry is inspired, so it is easy to believe this was the case with this writer. It is possible to give numerous examples of poetry that sounds like nonsense if read literally as some choose to do with the poetry in Genesis. The faith of a Christian is not dependent on a literal belief in every word in the KJV Bible. Our faith rests on our relation to God as revealed to us through Jesus. We worship God, not the Bible.
Christians believe the Biblical writings contain many great truths about God and human beings. Scientific research has also revealed many truths about God’s creation, his work. But we always need to be careful when making truth claims. Scientific truths and Christian religious truths are essentially different in many ways. Most of the essential truths in the Bible could not be discovered through scientific style research. These truths were discovered by people with a close relationship to God. Some would say these truths were revealed to them by God. These are truths about God and his relation to his creation, particularly his people. The truths produced by scientific research are answers to questions about the natural world. The question about the age of the earth is a question about this earth we live on, a very important part of the natural world. The answer will be found in scientific research not the Biblical book of Genesis.
(Copyright 2013 Benjamin F. Plybon. All rights reserved.)
I would be interested to hear your views on how the universe came into being. I have not yet been able to obtain a reasonable scientific or religious answer to this question. Is there an answer?
When I find it, I can finish my Novel---which stands at 85 thousand words and just needs a short explanation to finish it off.
Gerry.
Ben
I'm with you that the age of the earth, well determined by science, is not in conflict with the Bible, especially the poetry of Genesis. All good Christian should read your article. Unfortunately, many Christians are so close minded that they do not read anything other than religious dogma and propaganda.
Ron