Episode 154 - Impact Crater Pseudoscience Mishmash
Recap: Impact craters form the basis of, or fit into the claimed evidence for, several different kinds of pseudoscientific claims. In this episode, I review two of them and also discuss some sensational headlines and why those headlines were wrong.
- Audio Clips Used
- References and Resources
- Logical Fallacies / Critical Thinking Terms addressed in this episode: Misuse of Statistics, Gambler's Fallacy
- Relevant Posts on my "Exposing PseudoAstronomy" Blog
Introduction: I study impact craters in my day job. Much of that is spent literally drawing circles in order to map out craters on many different bodies in the solar system to do lots of different science stuff with them. Because the vast majority of my time is spent staring at a computer screen and tracing out these craters, I have a lot of time to listen to podcasts and radio programs, which is one way I get ideas for this show. Over my listenings, bits and pieces of different peoples' crazy ideas have used impact craters, and I've noted them down as potential podcast episodes. Unfortunately, when I went to do this episode, I couldn't find some of my notes, so I'm only going to be covering two claims today. The first one is going to be quick, and the second one is going to take some more time. And of course, I have clips for you from people making their claim, themselves.
Claim 1: First up is a claim that was so weird that I noted it down when I first listened to it in 2012. I'm going to let her make the claim herself because I can't really do it justice, but I have to give a bit of context. The claim is made by Rita Louise, who is a naturopathic physician (that's a different podcast) who was sharing her research into the genetic origins of humans through various ancient mythologies and cultures. She thinks that life started on Mars and then was transplanted to Earth. As justification for why we went from Mars to Earth, this is what she said. [Clip from Coast to Coast AM, 29 October 2012, Hour 3, starting 09:19]
"And when you look at the timeline on Mars, you find some really amazing things. Mars uh, formed like 4.5 billion years ago [...] within two million years, there was already blue-green algae on the planet. It was covered with water, and according to scientists, it was the period of time that life was most likely uh, would most likely be able to form on the planet. But then there was the Late, uh, Bombardment, meteor bombardment, which caused it to lose its magnetic core, and so it lost its gravitational field, which meant it lost its atmosphere. And so the planet became a dead planet."
Background: The Cratering Process
To understand this claim, I need to explain two pieces of background. First up is the impact cratering process itself.
Impact craters form when a bit of material from beyond the target body hits the target body with enough energy to excavate a cavity. This is pretty straightforward, and you can use the analogy of just throwing a really heavy weight into sand and see the process.
One place where the simple experiment that you can do yourself breaks down is the velocities involved. The material that strikes a planet or moon or whatever is moving really fast. We often can relate to things traveling at, say, 35 mph or 50 kph. That's driving around town speeds. Instead of traveling that distance per hour, though, now change it to per second. As in, the distance your car travels in town in one HOUR is the distance that a projectile in space will travel in one SECOND.
Roughly. It varies depending on where you are in the solar system because of our primary sponsor of this show, Johannes Kepler and his second law of planetary motion, where stuff at Mercury's distance from the sun travels up to about 70 kps and stuff out by Pluto closer to 2 kps. In comparison, New Horizons travels around 14-15 kps, which is similar to the average asteroid speed near Earth.
Getting back to how speed breaks things from the simple do-it-yourself analogy, when stuff travels that fast, it's called a "hypervelocity." Besides meaning that this is really fast, it means that special stuff starts to happen when you have a projectile that impacts a target at hypervelocity. The main thing is that the energy of motion is much, much stronger than the strength of the projectile and the target. They can both act not only like a fluid, but also can simply vaporize. This creates a tremendous explosion as all that energy is converted to the cratering process. This is how a projectile that's 50 m (150 ft) across can form a crater 1 km (0.6 miles) across and kill everything within a few miles in under a minute.
This also means that very little of the initial projectile will survive, and that much of the properties of the projectile will be lost, like its density, the material its made of, and even the impact angle. Unless the projectile hits the target at less than 5-10° relative to the surface, you're going to get almost a perfect circle in an idealized target. You only get a crater that looks like an obvious ellipse if the projectile hits at that almost glancing blow angle; otherwise, the hypervelocity impact and subsequent explosion is very close to symmetric.
The second way this breaks down is how big these things can get. Impact craters scale in size from micrometers to thousands of kilometers across. It's seriously hard for any of us to wrap our heads around what happens when a projectile 10s of kilometers or miles hits a planetary body at a hypervelocity and what happens next. It's especially hard to understand what happens when the projectile is within a factor of maybe 10 of the size of the target.
With that in mind, tuck it aside.
Background: The Late Heavy Bombardment
The next piece of background information is about the Late Heavy Bombardment. Which may or may not have happened.
From the standard model of solar system formation, lots of material slowly comes together to form bigger objects, and this process continues as objects continue to grow. Eventually you get planets, but you still have a lot of potentially large left-overs from planet formation. Those left-overs keep hitting planets and moons in what we tend to call Early Bombardment or Late-Stage Accretion. It is really just stuff still coming together but instead of pea-sized bits of material, we're talking mountain- to moon-sized pieces of material coming together, in this gross over-simplification.
Models of solar system evolution then have the impact rate quickly slowing down as these left-overs are removed, either by hitting other objects that we still have, or by being thrown out of the solar system in the same way that we use the planets today to give our spacecraft gravitational boosts to get to higher speeds.
But, some models have something happening some time around 3.8 to 4.2 billion years ago, or about 300-700 million years after the planets and other stuff formed. There was evidence for this in samples from the Apollo missions, but reinterpretations of those with modern techniques are now suggesting that this evidence isn't really there. But there's also dynamic evidence for this which I'll hopefully get to in a later episode with an interview with one of the guys who wrote the original paper on this.
Anyway, whether or not this happened, it is called the Late Heavy Bombardment. Late because it was around half a billion years after solar system formation, and Heavy Bombardment because a consequence of whatever caused it was that we got a huge spike in the impact rate, including of big objects. IF it happened, it's when we think most of the large basins on the moon formed, many of which on the nearside are filled with dark lavas which you can see with the unaided eye from Earth. These are impactors which were 10s of kilometers or miles across up to maybe over 100. This would also have been a "reset" time for Earth, sterilizing the surface if life had already gained a foothold, because so many large impacts in such a brief time would probably have heated the surface too much to support life.
And so, with those two pieces of background information, let's get back to the claim. What Rita basically said was that the Late Heavy Bombardment, when it happened on Mars, caused Mars to lose its "magnetic core," which caused it to lose its gravity, which meant it lost its atmosphere. So, step 1 is the bombardment, step 2 is loss of magnetic "core" (whatever that means), step 3 is it loses gravity, and step 4 is it lost its atmosphere.
If she had just started with step 2 and used that to go to step 4, she'd basically be correct. We think that when Mars lost its inherent magnetic field, it could no longer protect its atmosphere from most of the sun's solar wind, which are mostly charged particles that stream out from the sun. Each molecule from the sun that then hits a molecule of Mars' atmosphere can give it energy, which then can give it enough energy to escape Mars' gravity, and that's how we think Mars lost most of its atmosphere.
But step 1 does not cause step 2. And step 3 never happened. Step 3 first -- Mars still has gravity. Gravity has nothing to do with a magnetic field. Gravity is an inherent property of matter. Period.
As for step 1, this is why I gave you that background information. The Late Heavy Bombardment, or LHB for short, must have happened on Mars if it happened on Earth's moon and at Earth. It would have created many large craters on Mars. But, those large craters don't affect the core of the planet. I have a friend from grad school who's gone on to actually do most of these simulations, and they show that unless you're making craters that are literally THOUSANDS of kilometers across on Mars, it is not going to affect the core, and therefore it's not going to affect the magnetic field.
On Mars, we have two known craters - maybe three - that are thousands of kilometers across. The possible one dates back almost to the planet's formation, and we know it had a magnetic field after that. The other dates to maybe 4.3 billion years ago and it's magnetized inside of the crater, so we know the planet also had a magnetic field after that impact. The other one is not magnetized. But it's also the smallest of the three, and it's the youngest. So we could say that maybe that killed the field, except that if it would have, then the other two which are larger should have. So instead, we say that it formed after the magnetic field died. I should note that I'm intimately familiar with this particular research because a pair of papers came out in 2013 on the magnetization of these large impact basins -- one of them I was first author on, and the other one I co-wrote.
So there's no evidence that these big basins affected the magnetic field in the way that Rita claimed. And, I left out an important part: What the real science research shows is not that giant impacts would kill the magnetic field, but they would restart the magnetic field. Rita is claiming the exact opposite.
Planetary magnetic fields are caused by liquid iron and nickel moving around near the core and generating the field due to a pair of fundamental theories in electromagnetism that I'm not going to get into. We think that planetary magnetic fields die because the planet simply cools down, and the liquid iron and nickel simply solidifies and can no longer flow to produce the field. Hence, a bunch of impact energy delivered to the core could help keep it liquid and therefore help the magnetic field.
And so, that's the real science of what's going on here. Not only is Rita Louise wrong, but the real science pretty much says the opposite of what she claimed.
Claim 2: The second claim I want to talk about in this episode has to do with impacts on Earth around 12,000 years ago. Specifically, the Younger Dryas period, about 12,900 to 11,700 years ago. Many different "alternative" people have made various claims that all center around this period, but one of the common causes that they like to point to is some sort of impact event. This is especially promoted by people who claim things like ancient advanced civilizations that were lost, and they like to point to this period as when that loss happened.
Background: Younger Dryas
By way of background into this period itself, we had been coming out of the last glacial maximum that had started around 24,000 years ago and lasted until around 18,000 to 17,000 years ago. Earth was slowly warming back up, but some time around 12,900 years ago, over the course of just a few decades, Earth cooled by about 2–6°C (4–13°F), on average, which caused glaciers to advance back and the climate to be generally dryer.
This only lasted about 1200 years, and then Earth warmed back up and we've been continuing to warm since. With that in mind, I'm planning at least a four-part series on global climate change hopefully for 2017, so stay tuned for more on that.
Graham Hancock's Claims
With that background in mind, I'm going to play some clips for you from Graham Hancock. Some of you who listen to other shows may have heard of him. He's made his name in arguing for alternative history, where there were many advanced civilizations in the past that we have lost to history. His latest book, published in 2015, was a followup to his much more famous book from 1995, "Fingerprints of the Gods." The 2015 book is "Magicians of the Gods." He's one of the main promoters of the idea that the three main pyramids in Egypt align with the belt stars of Orion -- see episode 34 for more on that.
His 2015 book had the same basic thesis but updated to focus on the Younger Dryas period. He thinks that not only the start, but the stop of it was caused by a gagillion small fragments from a comet, both times. [Clip from The Higherside Chats, 25 November 2015, starting 06:20]
"I think NASA, in particular, which has– is charged with the responsibility and-and is the recipient of large amounts of public money, is charged with the responsibility of understanding our cosmic environment. NASA um is very, uh, misleading on the issue of the dangers that surround us in our cosmic environment. Um, it gives the impression um, you know, that-that there is no real danger to the Earth from comets or asteroids, and if there is a danger it's millions or hundreds of millions of years away. Um, and this is completely incorrect. We actually live in a very hazardous cosmic environment and a great many astronomers are drawing attention to this, and drawing attention in particular to what is the-the Taurid meteor stream which is this huge meteor stream 30 million km wide that is the debris trail of the comet that hit us not once, but twice, 12,800 years ago, 11,600 years ago, and as a matter of fact, a bit of that debris trail of that comet hit the Earth once more recently on the 30th of June, 1908, the so-called Tunguska event."
There are two things to say about this clip. First is the conspiracy about NASA. It's pretty much the exact opposite of what he says. NASA, as a policy, has been maintaining for years that we are going to be hit by an asteroid or comet, and that the only way to know when is to fund them to continue to do searches for potential impactors. But, NASA gets less than 0.5% of the US annual federal budget, and asteroid searches get cut just as everything else gets cut.
Second, there is, in reality, no evidence that what Graham Hancock said here is true about the Taurids. But I'm going to continue that line of thought after I play this next clip, which comes after the host asked about whether there was evidence for his claims from impact craters. [Clip from The Higherside Chats, 25 November 2015, starting 09:43]
"The impact, the primary impacts were into areas that don't leave massive craters. ... The primary impacts 12,800 years ago were on the North American ice cap ... . You have at least four objects in the range of half a mile to a mile in diameter coming in at 60,000 to 70,000 mph and impacting the ice cap. The craters are excavated in the deep ice. They cause a massive melting of the ice cap and the craters effectively vanish ... . What you get is shock effects under the ice and those shock effects, now that all of the ice is gone ..., can be measured on the ground. And in areas just outside the ice cap, in the northeast of North America, four distinct craters have now emerged that date back exactly to 12,800 years ago. So, so the question of craters is in the process of being answered by the team of more than 30 scientists who are working on this problem."
I had a thought to continue from before this clip, and that's about the Taurids. The Taurid meteor shower is an annual meteor shower that we see on Earth that tends to peak around October 10 and November 12. It occurs no earlier than September 10 and no later than December 10. It's called the Taurids because if you trace the paths of the meteors across the sky, they all converge in the direction of the constellation Taurus.
The Taurids share an orbit around the sun with the comet Encke. Some astronomers think that both Encke and the Taurids are the result of a breakup of a larger comet. By looking at how spread out the particles are in their orbit, we can trace this breakup to about 20,000 to 30,000 years ago.
So that could fit with what Graham was saying. Except that there isn't any evidence for it. I know he tells what sounds like a convincing story, but it's really (mostly) baseless, despite the evidence he claims, especially for the Taurids being responsible. First off, there's no way we can say what month something happened 12,800 years ago, so even if an impact caused the Younger Dryas, we can't tie it to the Taurids. Second, the Tunguska impact happened June of 1908. That's well outside the range for when we can get the Taurids. So even the one event where we do have a date, it simply can't work with his model.
Third, he says that we have "four distinct craters ... that date exactly to 12,800 years ago." That's simply wrong. There are many, many lists that exist online of impact craters on Earth, along with their locations, sizes, and ages. I could find absolutely none that date to 12,800 years ago, much less find four.
But, what Graham might be referring to is what are known as the Carolina Bays.
Robert Felix's Claims
For that, we get into some statements made by many people, but in particular I'm going to get into clips made by Robert Felix. Robert is not an alternative history person, he's an alternative reality person. He believes that Earth is not currently warming, he thinks it's freezing. He was frequently interviewed by George Noory on Coast to Coast AM as a first-hour guest and because of his frequency, they tended to talk about random things not necessarily related to global cooling. The Carolina Bays were one of those things back in 2010.
As setup to this clip that comes after a commercial break, just before the commercial break he was talking about Earth's magnetic field reversing at the start of the Younger Dryas. Which didn't happen. But he said it did, and when that happens, you get giant explosions in the sky that cause holes in the ground. [Clip from Coast to Coast AM, 07 November 2010, Hour 1, starting 22:11]
"The other part was these hol— holes in the ground, the Carolina Bays that-that I write about those in the book, and I've talked about them. And now we're finding Carolina Bays in Australia— I've had readers that've sent me photos that are, you know, screenshots from Google Earth, where you can see these huge Carolina Bays. If-if, if you have Google Earth, and you go go for instance to Borough, Alaska, and then you scroll down just a little tiny bet south of Borough, you will see these oval shapes that are, these holes that are blasted into the ground that are far bigger than the city of Borough itself. And it looks like there's hundreds of them there, just in a small area. In the United States, there are more than 2 million of these Carolina Bays. They– some of them are only the size of an acre, but some of them are as much as 6 miles across. Now it used to be that scientists thought that ... they look like swamps in the ground, but when the airplanes were invented and people were able to fly over they realized that all of these oval-oval swamps are all oriented in the same direction, north and south, and that some of them actually overlap each other and-and even though they may be 6 miles across, they're only 50 ft or less deep. And scientists have dated them, and they date to the Gothenberg magnetic reversal of 12,000 years ago. So these holes, whatever caused them, were blasted into the ground at a magnetic reversal."
After that clip, and the transition from discussing Hancock, the obvious question is, "What are Carolina Bays?" To be honest, I had never heard of them until listening to these folks. They're pretty neat.
Carolina Bays are the name for more than 500,000 elliptical depressions along the eastern coast of mostly the United States, though the vast majority are concentrated in the Carolinas. They are very regular in shape, span in size from a few hundred meters to a few kilometers in their long axes, and they are all generally oriented in a northwest / southeast direction for their long axes. This orientation changes to be more west/east as you go northward, and they very roughly converge in southeastern Indiana and southwestern Ohio. But this is approximate and many vary by several degrees over just a small area.
And so the next question is, what formed them? This is highly debated. Clearly, Robert Felix is claiming they were caused by an extraplanetary impactor, either swarm or something that broke up in the atmosphere and created individual craters. And, he thinks this happened about 12,000 years ago to explain the Younger Dryas. It's possible that this is what Graham Hancock was also referring to. And many other alternative folks make this claim, too.
But, there are problems with this, and I say that as a person who sees a circular feature on a planet and tends to think it's a crater first and ask questions later. But geologic context matters, and the standard things we have learned about cratering throughout the solar system still apply. As does methods of dating them.
First off, dating. Many different techniques have been used to try to date these features. To give you the answer first, NONE of them come even close to 12,800 years ago. Studying pollen trapped in the rims of these features gives ages around 75,000 to 134,000 years ago. Using principles of stratigraphy (see episode 137 for more on that), we get ages of about 27,200 to 36,000 years old. Using optically stimulated luminescence dating, we get 80,000 to 100,000 years old. And using radiocarbon dating, again of material trapped within the rim as well as core samples, we get ages for some of them of 440±50 years, most of them more than 14,000 years old and some ages of 27,700±2,600 years old.
In other words, while these different methods tend to disagree, they were mostly sampling different bays, and so they have a range of ages, anywhere from maybe 500 years ago for some, but most at least 27,000 years old and potentially more than 100,000 years old.
Note that no where there did I say that they were all 12,800 years old, 12,000 years old, nor 11,600 years old. So even if they are impact craters, they are not the age required and claimed by various alternative people.
But there are reasons to suspect they are not impact craters. Well, one in particular which I'll discuss here, and that's their shape. I've studied a lot of impact craters. I have traced the rims of over 2.6 million craters across the solar system, cataloging literally more than anyone else has manually done, ever. Never have I seen so many regularly elliptical-shaped craters on any planetary surface. Granted, I have never really studied Earth impact craters, and one could argue that Earth would be different than airless bodies like the moon, or nearly airless bodies like Mars. But that works both ways: Earth has an atmosphere and it has a very active set of surface modification processes. Even if these all date to 12,800 years ago - which they don't - but if they did, that's 12,800 years of active erosion that should have modified them. And these aren't in places that get little erosion: These are in wetlands and the alternative researchers have them sometimes forming from airblasts that hit in glaciers miles thick that then would retreat and melt, further modifying these features.
To put this succinctly: They are too regular at this point in time, in my opinion, to be impact craters.
Also, we don't need an impact event to explain them. Plenty of terrestrial geologic processes can explain these, primarily with periodic local wind patterns and lake formation. The orientation of the bays are consistent with wind patterns that were present during the previous-previous glaciation, the Wisconsin Glacial episode, which occurred around 150,000 to 50,000 years ago, so the non-impact model can explain even the seemingly weird and regular orientation of these features.
Mainstream Explanation for Younger Dryas
As for the Younger Dryas itself, there are mainstream researchers who think that it may have been caused by an impact event. Evidence for this comes from concentrations of material often attributed to terrestrial impact events in layers of rock that date to about 12,800 years ago, such as a concentration in platinum, nanodiamonds, and carbon.
However, this is not conclusive, and those who study the Younger Dryas do not have a consensus yet. Criticisms of the impact idea come from claims of incorrect dating of the layers and lack of other events that one would expect, such as a decline in the population of the native population in North America that can be linked to that time. In terms of the dating, when other researchers went back to the sites that people had claimed showed these increases in material linked to an impact, they found that very few - if any - of them actually dated to the Younger Dryas. These papers are as recent as 2014 and 2015, so as I said, this is still an active area of research.
The perhaps mainstream explanation for the Younger Dryas is changes in ocean currents, specifically the North Atlantic "conveyor" current which circulates warm waters from the equator northward. This could have been disrupted by an influx of fresh water due in part to us coming out of the previous ice age -- as the glaciers melted and deposited their water into the ocean, this could have disrupted the important ocean currents that help regulate temperature on our planet. Another probably less mainstream idea is that the jetstream changed due to changing topography as miles of ice melted, and this changing of the jetstream disrupted that important temperature regulator.
And finally, what about the Gothenberg magnetic reversal that Robert talked about? Long-time listeners may remember my episode about a magnetic pole flip not happening in 2012, and I stated in that episode that the last pole flip was 780,000 years ago. But, there have been geomagnetic excursions since then. A magnetic excursion is when Earth's global magnetic field stays intact, but may lessen somewhat, the pole may migrate a significant amount, and in SOME areas of the planet, it may change orientations. But, after this excursion, which may last a few thousand years, it goes back to the way it was. There was a geomagnetic excursion within 1000 years of the start of the Younger Dryas period. But that can't cause it, and it certainly can't cause a comet impact like what Robert is saying. A comet doesn't care about a planet's magnetic field. Not only is a comet not magnetically charged, but a comet is moving way too fast to have the field do much of anything, especially to prevent it from hitting a planet. So Robert is pretty much wrong on every count.
For a mid-episode wrap-up then, we have a few cases of crater-based claims that are more based in fancy than in sound science. It doesn't matter how sincere nor genuine the claimant may sound, that doesn't mean they are correct. It also shows that even some of the most basic claims they make that are then used to support their idea may not be correct in and of themselves. You really have to examine each and every part of what someone says to see if it's correct.
Or, to put it a different way, I just started to re-watch The X-Files, for I was a child of the 1990s but never made it through the whole series. I just watched an episode where Agent Scully had an apt quote: "The truth is out there, but so are lies."
New News: Impact Imminent!
With that in mind, reports emerged about two weeks ago as I record this, in mid-December 2016, that NASA claims an asteroid collision that will kill us all is imminent. At least, those were the headlines at the time. As I write and record this episode two weeks later, at the end of December, the headlines have been changed to things like, "NASA scientist warns we're not prepared for surprise asteroid or comet impact." This is going from, instead of NASA saying "the big one" is going to hit tomorrow, that we're just unprepared.
It's of course important to note this is in marked contrast with what Graham Hancock claimed that NASA says everything is rosy for the next few million years.
That gratuitous note aside, what was going on was that at the meeting of the American Geophysical Union that week, a scientist, who happened to be employed by NASA, gave a talk that the news media blew way out of proportion and then back-tracked on. The researcher was Joseph Nuth, who made a point of his talk to say that at this point in time, we don't have any viable method to deflect an asteroid that could cause a planet-wide, or really even city-wide destructive event.
What was taken out of proportion was his statement that catastrophic impacts are rare, "But on the other hand, they are the extinction-level events, things like dinosaur killers, they're 50 to 60 million years apart, essentially. ... You could say, of course, we're due, but it's a random course at that point."
So what the news media does in click-bait headlines is say that a NASA scientist says we're due for a dinosaur-killing extinction level impact into the planet.
This gets to what I said I'd talk about last episode in this episode, the misuse of statistics, specifically the Gambler's Fallacy. The Gambler's Fallacy can be most easily thought of with a coin toss. If I toss a coin one time, the chances of it being heads is 50%. Let's say it came up tails. If I toss a coin a second time, the chance of it coming up heads is also 50%. But under the Gambler's Fallacy, one would say that because it came up tails before, and the odds are 50%, then it's more likely to come up heads this time to even things out in the average. In fact, they would say it's a 3 in 4 chance to come up heads. But let's say it came up tails again. Well, on the third flip, under the Gambler's Fallacy, we'd think that this time it must have a 7 in 8 chance to come up heads. Even though in reality, it still has just the same chance of being heads or tails because each coin flip is independent.
As another example, I remember a sitcom from about a decade ago where a man went to the doctor to get a vasectomy. Being a stereotypical American male, he wasn't that happy about it and was trying to get reassurance from the doctor that it'd be fine and nothing would go wrong. He asked the doctor what his chances were of something going wrong, and the doctor said about one in 5000, but not to worry that none of his patients had ever had complications. He asked how many the doctor had done, and the doctor responded, "Oh, about 5000." The man got up and walked out.
That's the Gambler's Fallacy because he incorrectly thought that if his chances were one in 5000, and the doctor had done 4999 without a problem, that meant that by the 5000th, there would be a problem and because he was number 5000, he'd be the one with complications.
The exact same thing applies to asteroid impacts. Let's say that the numbers are correct, and Earth faces an impact event of a 10-mile-wide asteroid every 50 million years. But, we haven't had one in 65 million years. It's the exact same Gambler's Fallacy thinking to say that we're "overdue." The odds of getting hit any one year are exactly the same as the previous, about one in 50 million. It's only when we look at very long timescales, like in this case, a few billion years, that we can say there are this many hits in that time, and so the average is one per 50 million year time period.
So, that's the story behind those recent claims you may have heard about, or if you're listening to this in the far future -- yes, I'm talking to that listener who just picked up the show in 2018 and has been binge-listening to me for 20 hours -- then you know what's going on with this kind of claim.
Provide Your Comments:
No comments have been provided.