By the 18th century , a few naturalists were trying to place the age of the Earth on a scientific basis. The naturalist Mikhail Lomonosov , regarded as the founder of Russian science, was one of the first to undertake this exercise, suggesting in the mid- 18th Century that the Earth had been created separately from the rest of the universe, several hundred thousand years before. Lomonosov's ideas were mostly speculative, but in the French naturalist the Comte du Buffon tried to obtain a value for the age of the Earth using an experiment.
He created a small globe that resembled the Earth in composition and then measured its rate of cooling. This led him to estimate that the Earth was about 75, years old. Very few of their colleagues paid them much mind. Many left the question of the age of the Earth to creation mythologies, or simply assumed that the Earth always had been, always would be.
However, there were many naturalists whose studies of strata , the layering of rock and earth, gave them an appreciation that the Earth had been through many changes during its existence, however long that might be.
These layers often contained fossilized remains of unknown creatures, and there seemed to be a progression of types of such creatures from layer to layer. In the s, the British naturalist William Smith pointed out that if two layers of rock at widely differing locations contained similar fossils, then it was very plausible that the layers were the same age.
Other naturalists used this idea to construct a history of the Earth , though their timelines were inexact as they did not know how long it took to lay down such layers. Smith's nephew and student, John Phillips, later calculated by such means that the Earth was about 96 million years old. In , the geologist Charles Lyell took the next step and proposed that the features of the Earth were in perpetual change, eroding and reforming continuously, and the rate of this change was roughly constant.
This was a challenge to the traditional view, which saw the history of the Earth as static, with changes brought about by intermittent catastrophes. Many naturalists were influenced by Lyell to become "uniformitarians" who believed that changes were constant and uniform.
In , the physicist William Thomson who later became Lord Kelvin of Glasgow published calculations that fixed the age of the Earth at between 20 million and million years. He assumed that the Earth had been created as a completely molten ball of rock, and determined the amount of time it took for the ball to cool to its present temperature. His calculations did not account for the ongoing heat source in the form of radioactive decay, which was unknown at the time. Geologists had trouble accepting such a short age for the Earth.
Biologists could accept that the Earth might have a finite age, but even million years seemed much too short to be plausible. Charles Darwin , who had studied Lyell's work, had proposed his theory of the evolution of organisms by natural selection , a process whose combination of random heritable variation and fundamentally non-random cumulative selection implies great expanses of time. Even million years didn't seem long enough.
In a lecture in , Darwin's great advocate, Thomas H. Huxley , attacked Thomson's calculations, suggesting they appeared precise in themselves but were based on faulty assumptions. Huxley was correct, and in fact Thomson's estimates would prove far too short. Thomson had attempted to root the debate in one set of facts; the geologists and evolutionists had used others; and ultimately the latter two groups were proven more correct.
He certainly managed to provoke a long and productive debate. The German physicist Hermann von Helmholtz and the Canadian astronomer Simon Newcomb joined in by independently calculating the amount of time it would take for the Sun to condense down to its current diameter and brightness from the nebula of gas and dust from which it was born.
They came up with a value of million years, which seemed to set an upper limit on the age of the Earth that was consistent with Thomson's calculations. However, they assumed that the Sun was only glowing from the heat of its gravitational contraction. They knew of no other ways for it to produce its energy. Other scientists backed up Thomson's figures as well.
Charles Darwin 's son, the astronomer George H. Darwin of the University of Cambridge , proposed that the Earth and Moon had broken apart in their early days when they were both molten.
He calculated the amount of time it would have taken for tidal friction to give the Earth its current hour day, and concluded that Thomson was on the right track. In , John Joly of the University of Dublin calculated the rate at which the oceans should have accumulated salt from erosion processes, and determined that the oceans were about 90 million years old. Rock minerals naturally contain certain elements and not others. By the process of radioactive decay of radioactive isotopes occurring in a rock, exotic elements can be introduced over time.
By measuring the concentration of the stable end product of the decay, coupled with knowledge of the half life and initial concentration of the decaying element, the age of the rock can be calculated. Typical radioactive end products are argon from potassium and lead from uranium and thorium decay. If the rock becomes molten, as happens in the Earth's mantle , such non radioactive end products typically escape or are redistributed. Thus the age of the oldest terrestrial rock gives a minimum for the age of the Earth assuming that a rock cannot have been in existence for longer than the Earth itself.
By the turn of the 20th century , Thomson had been made Lord Kelvin in appreciation of his many scientific accomplishments. He had reason to feel confident of himself, and the fact that multiple attempts to determine the age of the Earth seemed to show that it was about million years old led him to feel very certain that his estimates were correct.
The geologists could only suggest correctly that Kelvin didn't have all the facts, and they still believed that the Earth was far older than million years.
The breakthrough that would ultimately resolve the conflict took place in , when the French chemist A. Henri Becquerel discovered radioactivity. In , two other French researchers, Marie and Pierre Curie , discovered the radioactive elements polonium and radium.
In Pierre Curie and his associate Albert Laborde announced that radium produces enough heat to melt its own weight in ice in less than an hour. Geologists quickly realized that the discovery of radioactivity upset the assumptions on which most calculations of the age of the Earth were based.
These calculations assumed that the Earth and Sun had been created at some time in the past and had been steadily cooling since that time. Radioactivity provided a process that generated energy. George Darwin and Joly were the first to point this out, also in There was the issue of whether the Earth contained enough radioactive material to significantly affect its rate of cooling.
Geitel , had detected radioactivity in the air and then in the soil. Other investigators found it in rainwater, snow, and groundwater. Robert J. Strutt of Imperial College, London, found traces of radium in many rock samples, and concluded that the Earth contained more than enough radioactive material to keep it warm for a long, long time.
Strutt's work created controversy in the scientific community. Lord Kelvin spoke for those who still believed in the older estimates, fighting a stubborn rear-guard action in public against the new findings up to his death in , though he admitted in private that his calculations had been shown to be incorrect. To feel completely vindicated, they needed to come up with new and more rigorous estimates of the age of the Earth.
Radioactivity, which had overthrown the old calculations, yielded a bonus by providing a basis for new calculations, in the form of radiometric dating.
Ernest Rutherford and Frederick Soddy had continued their work on radioactive materials and concluded that radioactivity was due to a spontaneous transmutation of atomic elements. An element broke down into another, lighter element, releasing alpha, beta, or gamma radiation in the process. Surely you know!
Or who stretched the line upon it? To what were its foundations fastened? Or who laid its cornerstone, When the morning stars sang together, And all the sons of God shouted for joy?
Where were you when I laid the foundations of the earth. No, my God, I have no understanding. Father, I have no idea about how you determined the measurements of the earth. No, Lord, I do not know. Morning stars singing together? Lord, this is beyond my ability to comprehend. Sons of God shouting for joy? Can I take a guess? Okay, Lord, I will be quiet. Thou art God. So, too, I cannot provide a certain answer to how old the earth is. I was not there when God created it.
I have the testimony of his Word, and from his Word, I will look out into the observable data that I find in the world. And when I do, I understand that the earth was created in six days, underwent a dramatic transformation. I understand the world was infected by the sinfulness of mankind. I understand that there was a time when rain was unnecessary, for a mist went up from the earth.
There was a flood. Once more, the very constitution of the earth and life on it changed. Things were too different. I have the genealogy. I trust that. But when I returned to the founding of the world in six days, I have God asking me if I was there when he created everything? He is challenging the presumption of man to explain what God did before he ever created man. I will tell you what I do know about the history of the world. The Apostle Paul tells us in 1 Corinthians 15 that all of time is centered in one transformative event in the world: the resurrection of Jesus Christ.
Everything that has happened before and everything that has happened afterward, or will occur, is marked by the central act in cosmic history, the resurrection of Jesus Christ.
I might not know how old the earth is, but I know the One who made it. I place my trust in Him. I have absolute certainty that the resurrection of Jesus Christ has changed everything. There is one final cataclysmic event that will happen in the earth and the cosmos: the second coming of Jesus Christ, the judgment of the world, and an extraordinary molecular rearrangement of all things that will bring about a New Heaven and a New Earth. And here is the most important thing I could write: your faith or unbelief in the resurrection of Jesus Christ determines whether you will be part of that New Heaven and New Earth.
I cannot date the age of the earth because so many things have changed. But I can say with certainty that because Christ is risen from the dead so we will rise again from the dead. We will live with him in a new heaven and new earth forever.
I do not fully understand even that. From modern-day eruptions, we know that active volcanoes grow by perhaps a meter every century. The highest point on the big island of Hawaii is Mauna Kea at 4, meters above sea level. However, the volcano rises approximately 10, meters above the ocean floor, so a rough calculation gives its age:.
The Hawaiian Islands are a chain of volcanoes, each formed from layer after layer of lava. A new island dubbed Loihi is now forming south of the big island. This is a rough estimate, to be sure, but it jives well with other methods that date the big island of Hawaii as about a million years old. The other islands that string out to the northwest, each with now-dormant volcanoes, are progressively older and a new island, dubbed Loihi, is already forming as volcanoes erupt on the ocean floor southeast of the big island.
You can do a similar calculation to date the Atlantic Ocean, which is about 3, kilometers wide and grows wider every year. These continents were once joined into the supercontinent Pangaea; the Atlantic Ocean formed when Pangaea split down the middle and formed a divergent boundary, now marked by the Mid-Atlantic Ridge Fig.
New crust forms along the Ridge, as Europe and Africa move away from the Americas. Exacting satellite measurements over the past two decades reveal an average spreading rate of 2. The Atlantic Ocean formed when the supercontinent Pangaea began to split apart about million years ago. Source: USGS. This rough estimate of about million years is close to other measurements of the age of the Atlantic.
It is remarkable to imagine that a great ocean, a seemingly permanent feature of our home planet, is so transient in the context of Earth history. A third simple calculation reveals even longer time spans. The Appalachian Mountains are now gently rounded and relatively low—mostly below 3, meters high Fig. But geological evidence reveals that they once were the grandest mountain chain on Earth, rivaling the Himalayas in ruggedness and height with some peaks at more than 10, meters.
Ever so gradually, erosion has worn the Appalachians down to their present state, but how long might that process take? The gently rounded Appalachian Mountains a were once the tallest and most rugged mountain rage in the world, rivaling the modern Himalayas b. Hundreds of millions of years of erosion were required to achieve their present appearance. The volume of this impressive mountain is thus:.
Now, imagine a stream that flows down the side of this mountain. Mountain streams carry silt and sand downwards—a key factor in erosion. All of these sediments came from higher up the mountain, which is constantly being eroded away. To estimate how long a mountain might survive against erosion, consider a mountain with six principal streams.
A typical stream might carry an average of one-tenth of a cubic meter of rock and soil a few shovels full per day off the mountain, though the actual amount would vary considerably from day to day. Over a period of a year, the six streams might thus remove:. That means every year on the order of cubic meters of material, or about 20 dump trucks full of rock and soil, might be removed from a mountain by normal stream erosion. If the mountain streams remove about cubic meters per year, then the lifetime of the mountain can be estimated as the total volume of the mountain divided by the volume lost each year:.
This estimate is certainly rough and not directly applicable to any specific mountain. Nevertheless, a few hundred million years is but a small fraction of a few billion years. How can we say Earth is 4. The physical process of radioactive decay has provided Earth scientists, anthropologists, and evolutionary biologists with their most important method for determining the absolute age of rocks and other materials Dalrymple ; Dickin Trace amounts of isotopes of radioactive elements, including carbon, uranium, and dozens of others, are all around us—in rocks, in water, and in the air Table 1.
The rest of the uranium will have decayed to , atoms of other elements, ultimately to stable i. Wait another 4. Radiometric dating relies on the clock-like characteristics of radioactive decay.
In one half-life, approximately half of a collection of radioactive atoms will decay. Source: NCSE. The best-known radiometric dating method involves the isotope carbon, with a half life of 5, years. Every living organism takes in carbon during its lifetime. At this moment, your body is taking the carbon in your food and converting it to tissue, and the same is true of all other animals. Plants are taking in carbon dioxide from the air and turning it into roots, stems, and leaves.
But a certain small percentage of the carbon in your body and every other living thing—no more than one carbon atom in every trillion—is in the form of radioactive carbon As long as an organism is alive, the carbon in its tissues is constantly renewed in the same small, part-per-trillion proportion that is found in the general environment.
All of the isotopes of carbon behave the same way chemically, so the proportions of carbon isotopes in the living tissue will be nearly the same everywhere, for all living things.
When an organism dies, however, it stops taking in carbon of any form. From the time of death, therefore, the carbon in the tissues is no longer replenished. Like a ticking clock, carbon atoms transmute by radioactive decay to nitrogen, atom-by-atom, to form an ever-smaller percentage of the total carbon.
Scientists can thus determine the approximate age of a piece of wood, hair, bone, or other object by carefully measuring the fraction of carbon that remains and comparing it to the amount of carbon that we assume was in that material when it was alive. If the material happens to be a piece of wood taken out of an Egyptian tomb, for example, we have a pretty good estimate of how old the artifact is and, by inference, when the tomb was built.
The result: the two independent techniques yield exactly the same dates for ancient fossil wood. Carbon dating often appears in the news in reports of ancient human artifacts. In a highly publicized discovery in , an ancient hunter was found frozen in the ice pack of the Italian Alps Fig. The technique provided similar age determinations for the tissues of the iceman, his clothing, and his implements Fowler Carbon dating revealed that he died about 5, years ago.
Photo courtesy South Tyrol Museum of Archaeology, www. Carbon dating has been instrumental in mapping human history over the last several tens of thousands of years. When an object is more than about 50, years old, however, the amount of carbon left in it is so small that this dating method cannot be used. To date rocks and minerals that are millions of years old, scientists must rely on similar techniques that use radioactive isotopes of much greater half-life Table 1.
Among the most widely used radiometric clocks in geology are those based on the decay of potassium half-life of 1. In these cases, geologists measure the total number of atoms of the radioactive parent and stable daughter elements to determine how many radioactive nuclei were present at the beginning.
Thus, for example, if a rock originally formed a long time ago with a small amount of uranium atoms but no lead atoms, then the ratio of uranium-to-lead atoms today can provide an accurate geologic stop watch. When you see geologic age estimates reported in scientific publications or in the news, chances are those values are derived from radiometric dating techniques.
In the case of the early settlement of North America, for example, carbon-rich campfire remains and associated artifacts point to a human presence by about 13, years ago.
Much older events in the history of life, some stretching back billions of years, are often based on potassium dating. This technique works well because fossils are almost always preserved in layers of sediments, which also record periodic volcanic ash falls as thin horizons.
Volcanic ash is rich in potassium-bearing minerals, so each ash fall provides a unique time marker in a sedimentary sequence. The rise of humans about 2. Paleontologists rely on radiometric dating to determine the ages of fossils, such as this million-year-old trilobite, Ameura major , from near Kansas City, Kansas.
Photo courtesy Hazen Collection, Smithsonian Institution. The oldest known rocks, including basalt and other igneous formations, solidified from incandescent red-hot melts. These durable samples from the moon and meteorites are typically poor in potassium, but fortunately, they incorporate small amounts of uranium and other radioactive isotopes.
As soon as these molten rocks cool and harden, their radioactive elements are locked into place and begin to decay. The most ancient of these samples are several types of meteorites, in which slightly more than half of the original uranium has decayed to lead.
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