Episode 137 - Why Earth Is Old, Without Radiometric Dating
Recap: Most often when discussing the age of the Earth or the solar system, scientists refer to radiometric dating. In kind, young-Earth creationists will try almost exclusively to poke holes in radiometric dating. But, before radioactive decay was discovered over one century ago, scientists in many different fields had already concluded that Earth was at least millions, if not hundreds of millions of years old. This episode discusses the reasoning they used.
- Wikipedia: Age of the Earth
- Scientific American: "How Science Figured Out the Age of the Earth"
- Talk Origins: Geologic History
- American Museum of Natural History: Harry Hess and the Discovery of Seafloor Spreading
- Logical Fallacies / Critical Thinking Terms addressed in this episode: Non sequitur (related to Episode 133)
- Relevant Posts on my "Exposing PseudoAstronomy" Blog
Claim: The basic, fundamental claim in this episode comes from young-Earth creationism: Earth is only 6000 years old, or at least less than 10,000. Modern-day creationist arguments against the scientific claims for the age of Earth almost exclusively focus on alleged flaws in radiometric dating methods. I already spent two episodes on that, back in #38 and 39. But, I haven’t really talked about other evidence that Earth is old. Why scientists think Earth is old comes from a large number of fields, and radiometric dating methods are really the new kid on the block. So this episode is going to focus more on those other reasons and lines of evidence, so that if you’re ever in a conversation with a young-Earth creationist, you don’t even have to touch on radiometric dating.
One of the most basic, early assumptions is that Earth is at least as old as the oldest recorded human civilization. Many will look to Egypt for that, but young-Earth creationists don’t have to do any real manipulation to get something less than 6000 years old: There is no continuous, recorded Egyptian history that goes past about 5000 years ago. However, there is plenty of evidence for civilization before recorded history, but it’s easier for young-Earth creationists to compress that time period. Where the YECs have to massage dates is to fit the chronology into the Genesis flood and Exodus.
We can also look to ancient Sumer. Unfortunately, that also gets us back to about 5000 years ago, though as with ancient Egypt, there is copious evidence of non-continuous written history before that. Unfortunately, much of it is impossible to date.
And so, with recorded history, we get to what young-Earth creationists would say is about the year 1000 for Earth’s existence, which is about 40 years after the death of Adam, if I remember correctly. If one were a cynical person, they might point out that this makes sense for a religious text to not start after continuous recorded records and not be incredibly surprised that this basic check doesn’t get us beyond 6000 years.
And so, Bishop Ussher, in his Annals of the World, volume 4, published in 1650, used the genealogy of the Christian bible to place the date of creation as, “The evening of Sunday, October 23, 4004 BC.”
With the scientific revolution in Europe, scientists were making names for themselves by rejecting previous assumptions and then examining what falls out of it. So, what happens if we reject recorded history as our benchmark for the age of Earth? Where else can we look to try to figure how old the planet is?
The obvious place is the planet itself.
Enter George-Louis Leclerc, Comte de Buffon (1707-1788), who was a French naturalist, mathematician, and cosmologist. He is credited as the father of all thought in natural history in the second half of the 18th century, and he wrote 36 volumes of his Histoire Naturelle during his lifetime.
He was one of the first modern scientists who look beyond religion to try to understand the world, and in the opening volumes of his natural history, he outlined a history of Earth with little relation to what was in the Judeo-Christian Bible. He was condemned by the Faculty of Theology at the Sorbonne, which was the University of Paris at the time. He retracted his claims to avoid problems.
In later volumes, specifically in 1778, he went as far as saying that the Bible was completely wrong with how Earth formed. He proposed that planets were created by a cometary collision with the sun, and he made many assumptions that led him to conclude that the center of Earth was composed of an iron sphere of a certain size. He had run experiments to see how fast different spheres of iron cooled in the lab, scaled up, and calculated an age for Earth of 75,000 years. He was again condemned by the Sorbonne, and he again retracted his claims.
Nearly a century later, in 1862, Lord Kelvin in Brittish-land tried to refine Leclerc’s models, and with the new mathematical models and based on the current temperature of Earth, he got an age of 20-400 million years. He assumed Earth had formed as a molten object and then he calculated how long it would take the near surface to cool to its current temperature.
This is a very large range. It is also based on assumptions that we now know are wrong because we have much better models for how Earth formed and we know Earth’s structure and temperature profile pretty well. But getting the “right” answer here is almost besides the point: It was some of the first serious, scientific attempts to start from non-dogma and try to figure out how old Earth is. Not only that, but the answers that they publicly published were significantly older than the biblical timeline, which contradicted the very powerful Catholic Church at the time.
And, other physical arguments were made. Physicist Hermann von Helmholtz in 1856 calculated an age of 22 million years, while astronomer Simon Newcomb in 1892 calculated 18 million years. They both used the same mechanism, assuming that the sun formed from a vast nebula and calculating how long it would take to condense to its current diameter and brightness. We now know that at least one of their major assumptions was wrong, since they assumed the sun was only glowing because of gravitational squeezing rather than by nuclear fusion, since they didn’t know of the fusion process.
Astronomer George Darwin, son of Charles Darwin, entered the fray as well, and he calculated around the turn of the century an age of 56 million years. He got this from a faulty method for how the moon formed (unless you’re Mike Bara), that it formed from a molten, rapidly spinning Earth. He then calculated the amount of time for mutual tides to slow down the rotation rate such that Earth would have its current 24-hour day.
Again, the point so far is not necessarily that these scientists used faulty assumptions, but that they were trying to do things from first principles, and they were getting ages far, far older than what the Church was teaching.
Geologic Processes and Uniformitarianism
If you want to try to understand the age of the Earth, perhaps the logical first step is to avoid physics, avoid archaeology and history, but rather look to Earth itself. Geology was becoming a legitimate scientific field in the 1700s and 1800s, and these scientists were traveling the world and made many different discoveries.
For example, one discovery was that parts of Earth that were now clearly barren had once been covered by water. While one could explain this biblically with Noah’s flood, geologists were starting to understand sedimentology - how material is laid down by water - and they could easily tell the difference between single, massive, catastrophic events (like a world-wide flood) versus years upon years of slow deposition. And they saw slow deposition. This meant that at some point in the past, there had to be a very different climate in the area. And that during that very different climate, there had been many years worth of very slow deposition of rocks by water.
Another line of evidence was mountain ranges. Geologists were beginning to understand that mountains were not static, that they grew and eroded with time. They also realized that at some point in the past, the tops of many tall mountains must have been at sea level, for the tiny fossils of sea life could be found now many thousands of feet off the ground. With current maximum growth rates for mountains, one can then easily determine that Earth must be very old.
Those two examples skip some steps in between that I’m now going to go back to and motivate. One of the fathers of modern geology was James Hutton, who perhaps was the Scottish counterpart to George-Louis Leclerc, living from 1726 to 1797, and he originated the idea of uniformitarianism: Earth’s crustal features formed by relatively slow means of natural processes over long periods of geologic time, and those processes that we observe today were taking place in the past. Hence, uniform with time. Because of his work, he is often called the “Father of Modern Geology."
But Charles Lyell is usually better known, and he was born the year Hutton died, and he lived until 1875. Lyell rapidly became the foremost geologist of his day, literally writing the book on Geology: Principles of Geology, ©1830, with later volumes, editions, and follow-up work throughout his life. He popularized Hutton’s uniformitarianism ideas which were in marked contrast to what Christianity was teaching.
Lyell used uniformitarianism along with the two other principles of geology: Superposition and original horizontality. Superposition means that if something is on top of something else, it happened after the thing below it. In other words, if I see many layers of rocks in a roadcut, then the ones on top formed later than the ones on the bottom. The axiom of original horizontality is that stuff is deposited horizontally. In other words, you’re not going to see sediments from a river form in vertical layers. So if you see layers of rock that are not horizontal, than something happened to lift one end more than the other. Living in the Rocky Mountains, I see this all the time.
So, Lyell used these three principles of geology, or axioms of geology, and he traveled the world looking at different geological formations and mapping them. Over the course of those observations over his lifetime, he came to think that the Earth was at least 300 million years old.
The influence of the principle of uniformitarianism is hard to understate, for it influenced much of the field of geology and still influences it today: We assume uniformitarianistic processes unless there is evidence to the contrary. And there is, in many cases, and those cases are well known. For example, many volcanoes tend to give you a punctuated equilibrium, where you have a catastrophic event that changes things very rapidly, and then things are fairly static for a much longer period of time. Young-Earth creationists will often point to these events as clear evidence that uniformitarianism is wrong, but in doing so, they willfully ignore two key points: First, that geologists know about these exceptions and don’t claim them to be non-catastrophic events; and second, that most events in geology are still uniformitarianistic, and not catastrophic.
Other Geologic Reasons
To regroup a bit, I told you that the point of this podcast episode was to tell you how to argue how old Earth is without using radiometric dating to get an old Earth. So far, I’ve taken you through some of the history, and some of the arguments from early physicists and astronomers that were wrong but still got very old ages, relatively speaking to 6000 years. The best arguments for an old Earth, I think then, still come from geology. I already told you about mountain building and sediment deposition, but there are other good arguments to be made.
One such argument is ice core samples. In arctic areas with permanent snow and ice coverage, every year there is a layer of snow that is deposited. In summer, when it heats, the upper parts can melt a bit and form a crust. The next year, more snow falls on top, and the cycle repeats. After a few decades, the weight of the overlying layers compacts the snow below it into a single and distinct layer of ice, one for each season. By a process very analogous to tree ring dating, we can simply count the layers of ice in ice cores and get back literally hundreds of thousands of years, showing that these currently permanently iced over areas must have existed at least that long.
Another argument for the age of Earth comes from the salinity of the oceans, and this was used over a century ago, in 1899 and 1900, by John Joly. He observed current erosion rates of salt-bearing rocks. He estimated the volume of Earth’s oceans. Assuming you start with fresh water and that salt is added by erosion of rocks into the oceans, you can calculate an age of the oceans of 80 to 100 million years.
A problem with this technique is that it ignores that water is cycled into subduction zones in Earth, effectively including a source for salt, but ignoring a sink. But this doesn’t hurt the technique as a MINIMUM age estimate: While we now know that the oceans have reached a roughly steady-state for salinity, it probably took 80-100 million years to get to that salinity in the first place.
A third extra geology argument comes from seafloor spreading, a relatively late argument to the field, and one that only gives you the age of the Atlantic ocean if you assume uniformitarianism. But it’s a method nonetheless. Harry Hess was a World War II naval officer. He did something he wasn’t supposed to do: He left his vessels’ sounding gear on constantly, bouncing sound waves off the ocean bottom, effectively mapping it. This later led to the discovery of the mid-Atlantic ridges, which held between them a valley. In 1962, Hess proposed that the ocean floor is only a few hundred million years, much younger than the rest of the Earth’s crust as known at the time, but that it was continuously replenished from this rift running through the Atlantic ocean, and connected with other rifts throughout the world. This supported the relative young theory of continental drift, but more importantly, from current spreading rates, we could again arrive at a minimum age for the Atlantic Ocean, and it was many tens to hundreds of millions of years, in marked contrast with less than 10,000.
Throughout the last few hundred years, in response to the mounting evidence from geology, young-Earth creationists by and large responded to these ideas by claiming Divine Catastrophism: that one or two major, catastrophic events were responsible for everything that geologists were seeing. Mainly Noah’s flood, explaining everything. Sometimes events of the Fall were also linked in.
But unless the flood was magic, it really could not explain everything. And I mean that. The Flood would somehow have to, for example, lay down sediments in one go but make it look like they were laid down over many years. Somehow make it look like ice cores had yearly layers that went back tens of thousands of years. Raise some mountains while lower others. Flip Earth’s magnetic field many different times, all in a year, while spreading out the sea floors very rapidly and shifting continents to make it look like they were laid down over millennia.
And that’s why I summarized the argument this way in a presentation I gave at Skepticamp a few years ago: If you want to believe in Young-Earth creationism, then at this point, your God is a dick. If I’ve offended some listeners, you should re-examine your beliefs at this point, because there’s simply no other way to think about it. Your deity created a world with the appearance of vast, old age. Everything - except for the writings in one book - tell us that it is old. All of the curiosity, ability to reason, and ability to explore that your deity gave us tell us that it’s old. And yet, it’s young. Just to prove some point? To me, that’s a pretty dickish move.
I’ve skipped over a lot of interesting history of science in this podcast episode. I have a few links to more resources in the shownotes at podcast.sjrdesign.net, and in particular, there’s a good Scientific American article that I’ve linked to that gives a more chronological version of the story, leading up to radioactivity.
And radioactivity is really where it’s at. Very few places on Earth show areas that are more than a few tens to hundreds of millions of years old, and that’s because geologic processes on our planet happen so quickly that you do reach a steady-state, where you can only get a minimum age of how long it took to at least get to that steady-state. While that gives us 10s to 100s of millions of years, it’s radioactivity that lets us date the rocks to get to billions of years.
But even that is unimportant when you contrast it with the young-Earth creationist viewpoint of only a few thousand years. Tens of millions is enough to say that the young-Earth creationist age is wrong.
And, besides radioactivity, I’ve left out arguments from several other fields. In particular, I’ve left out astronomical arguments, like the speed of light (discussed in Episode 81). I’ve also left out biological and evolutionary arguments. Though that field in particular is key to leave out of this discussion because it is a non-starter if you were to try to have this discussion with a young-Earth creationist.
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