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Episode 41: Crater Age Dating and Young-Earth Creationism, Part 2

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Recap: A detailed look at a few different methods that young-Earth creationists use to try to show that craters really do indicate that the Earth-Moon system (and universe as a whole) is only 6000 years old.

Q&A: This comes from expat and a few other people: "Is there statistical information about the angle at which incoming rocks have struck, say, the Moon to create craters? Commonsense would suggest that a perfect 90° would be a rare event, and yet most craters seem to be perfectly circular or nearly so. I guess another way of asking this is, can an oblique impact create a circular crater and if so how?"

The answer to this question is that this particular aspect of the formation of craters is not intuitive. You'd think exactly as expat said, that only craters that hit something at a 90° angle are going to form a circular crater. The average impact angle is going to be 45°. Your common sense tells you that only a 90° impact should form a circle because if you chuck a rock at an angle into dirt, you form an ellipse, not a circle.

Instead, a better analogy is to throw a rock into a pond. You get a circle almost regardless of the angle. Unless the angle is VERY shallow, and we're talking somewhere around 10° here as "shallow."

This is a better analogy due to the viscosity of water versus rock, and the velocity of you throwing a rock versus a meteor about to strike a planet. The velocities are so high when a meteor strikes that it's effectively an explosion, and that explosion is going to be very close to circular almost regardless of the impact angle. As opposed to you throwing a rock into sand, that's not an explosion.

Experimentally, we expect that craters will start to look elliptical when the impact angles are below about 10°. This has borne out in both lab experiments and computer models.

It's also been shown to roughly be the case in observations. Surveys have been done - including my own research, and I've published twice on this - and these surveys generally back up the modeling and experiments.

It's also been shown to roughly be the case in observations. Surveys have been done - including my own research, and I've published twice on this - and these surveys generally back up the modeling and experiments.

There are also some subtle effects of crater diameter where the larger the crater is - and we're talking when you get on the size of 1000 km or more - the more elliptical it will be. So take, say, 10 km-diameter craters. Chances are only around 5% that the crater will form as an elliptical one. But once you get to 1000 km, chances are closer to 15-20%. Models show the distribution is pretty flat between about 5-100 km, is significantly less at smaller sizes, and significantly more at larger ones.

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Transcript

Intro: The topic I'm going to talk about today is the young-Earth creationist take on crater age dating. Unlike radiometric dating where the creationist arguments are incredibly varied and creationists will argue about everything from the fundamentals of whether radiometric dating even works to subtleties like carbon sinks, their arguments about craters are generally more subtle. This is probably because it's hard to deny the basic fact that craters form and if something has more craters it's older. So this episode is going to have around four different claims that creationists try to use to disprove old ages from craters.

And I'll say right off the bat that none of them are that the chronology from absolute dating of lunar samples that GIVE us those "billions of years" for the moon is wrong 'cause radiometric dating is wrong. I couldn't find that in ANY of the creationist sites that I looked at. I'm not sure why. Perhaps it's too obvious, or perhaps they are just unaware of the basic calibration of how we tie ages to crater densities. Maybe they should listen to my podcast.

Generic Quote Mining

I'm going to open this without a specific claim, but rather a few claims put out by the Creation Wiki against craters.

Their first objection is that our estimates of how long it takes craters to appear to degrade over time due to space weathering is wrong and that new research suggests it's much faster, quoting a NASA person who stated, that space weathering "takes place very rapidly on the Moon."

So you know the terms, space weathering is where tiny particles that are high energy stream out from the sun and can impact the surfaces of objects or atmospheres. These tiny particles don't do much of anything by themselves, but over many years and with so many of them, the effect adds up and can both chemically and physically change a surface.

Unfortunately, the wiki's reference for this is no longer active given that it's an internet article from 11 years ago. After a lot of searching, I was able to find the original story archived on a mailing list archive that I'll link to in the shownotes.

The article says absolutely nothing about space weathering beyond the non-quote. And, all the current research that I know of still says that it takes around a billion years for space weathering to remove just crater rays, to say nothing about the crater itself. So it's up to the creationists to still prove their point here.

The second of three problems that the Creation Wiki article points to is a claim from Peter Brown of the University of Western Ontario, where he "insist[s] that there is no absolute criteria for the dating of craters."

This would seem like a damning quote from a scientist that creationists are often fond of. But as with most creationist quotes from scientists, this one has been mined. The subject of Brown's quote is that he was discussing whether or not a 1953 photograph of the moon showed an impact event as it was happening.

If you read the actual article, Brown was saying this in the context of being able to date one specific crater to a 50-year time frame. In that sense, he is quite right, there is absolutely no criteria that we can use for getting an age like that unless someone saw it happening, which this article was talking about and looking for independent evidence. Even if we could get there and get a rock sample from that crater's melt sheet, we still would not be able to use any radiometric dating technique that we know of to get an age to the 50-year level of accuracy, and none of the techniques for dating rock let you get ages this young, either.

CreationWiki's third argument has to do with ghost craters, which is the main first solid subject I want to talk about in this episode.

Claim: Ghost craters on the moon mean that all the maria formed at the same time in just a matter of days, meaning the cratering rate was much higher than "secular scientists" think meaning that everything fits in a 6000-year timespan.

It's a claim put forward by the young-Earth creationist astronomer Danny Faulkner. It is quoted in almost all general discussions of craters and ages in young-Earth creationist literature.

Unfortunately for them, the entire idea behind this claim is based on a false premise. In the moon's history, we think there was a period of time around 4.2 to 3.8 billion years ago that corresponded to a heavy bombardment spike of impactors. One popular model to explain this is called the "Nice Model" because it was developed over beers by four dynamicists while at a conference in Nice, France. The model says that Jupiter and Saturn formed closer to the Sun and that a few hundred million years later, their orbits were excited, they danced around, and settled in their current orbits. This would have disrupted the asteroid belt and sent a lot of debris hurtling towards the inner solar system while this was going on, and caused the bombardment.

This bombardment corresponds with when the majority of the largest lunar basins formed, and those basins on the nearside are presently filled with flooded lavas and we see them as mare. Based on all the geologic evidence that most geologists and astronomers have, the basins formed and they thinned the crust under them. They were perfectly fine being big, deep craters for a hundred million years or so, but over time magma reached closer to the surface and was able to breach the crust in the thin areas - where these basins were on the nearside. That's what flooded them.

So there was a long time period still during the heavy bombardment when a lot of craters formed in the basins. After the flooded, the larger craters had rims that were high enough to sometimes still poke through, or to cause a circular hill in the solidified lavas. These are called "ghost craters."

What Dr. Faulkner says, though, is that the formation of the basins themselves almost immediately caused a breach of the crust that caused magma to pool and flood. The fact that ghost craters exists, according to Faulkner, means that the cratering rate must have been incredibly high so that enough craters would form in the day or two between the formation of the basins and the flooding of the volcanism. Hence why I said that this claim is based on a false premise.

Besides not fitting with the geologic evidence, it doesn't match with very basic physics. When a crater forms, it heats things up. When a basin forms, it heats things up A LOT and will melt the rock nearby, forming what we call impact melt. You can you very basic thermodynamics to calculate how long it takes the rock to cool. For basins 1000 km across, the timescale is somewhere on the order of thousands to tens of thousands of years. Again - this is very well-established physics that, if wrong, would have implications for how long it takes water to boil or soup to cool down.

Meaning, unless you had God cooling the rocks really fast, craters would not be able to form at all in the time between when Faulkner wants the basins to form and the magma to pool to form the maria.

Claim: Lunar craters were produced first during the Fall, then during the Flood, with the maria forming immediately after the Fall.

This is a model put forward by Danny Faulkner in the 1999 edition of the venerable "Journal of Creation." The basic problem, of course, is that normal scientists say that craters have formed over the past 4.5 billion years, but creationists somehow have to fit everything into 6000 years.

Faulkner uses the argument about ghost craters - that I just explained is a fallacious argument - to claim that the cratering rate must have been MUCH higher earlier on in the moon's history. This means that, if the rate was much much higher, you can compress 4.5 billion years into 6000. Very basic math indicates that you need a cratering rate around a MILLION times more than what we've estimated for the impact rate back then, which itself is around a 10,000-100,000 times more than what we think it is today.

That's an expletive-load of impactors. You'd think that the ancient civilizations that were around that we have real documentation for that creationists don't dispute would have noticed 100 BILLION times the impactors we see today. But anyway ...

The real crux of this argument requires that all of the lunar maria - those dark parts - formed at the same time and formed very quickly. Faulkner argues that it was the initial formation of these giant craters that actually CAUSED them to be flooded by volcanic material, but that's not what we really think. We know that the time the basins formed was separated in time from when they flooded with lava.

So, when Faulkner assumes that the impacts that formed these must have only happened in one small part of the moon and not at all on the far side, he's wrong. The impacts happened all over. It was the near side that later flooded with volcanism likely because the core is offset and the crust on the nearside is much thinner.

I realize the last minute or two may have sounded technical, so I'll summarize: Faulkner assumes one thing from science, but he is wrong. He takes that assumption from actual science and then uses it to shoehorn in a 6000-year timescale.

Faulkner does propose two tests of his model, but one of them produces something that is non-unique to it, and the other that he expects to be false is actually true.

Something that Faulkner's model cannot explain is that craters that formed AFTER the maria, which are all supposed to have been emplaced during Noah's Flood and so formed at the same time, actually show a range of ages. This range is seen in the brightness of the rays from the craters. Craters that still have bright rays, such as Tycho that has rays that can be seen over the entire near side of the moon, are younger than those that don't have rays because the rays disappear over time. We estimate that craters with rays on the moon are about 1 billion years old, while those that don't have rays are older. Since the maria formed about 3.5ish billion years ago, we do see both kinds on top of the maria, but Faulkner's model is that there should only be one.

Claim: Secondary craters means there is a literal "crisis in crater count dating."

The final claim I want to talk about in this episode is about secondary craters, something I mentioned at the end of the last episode. To recap, the basic idea behind crater age-dating is that craters form randomly over a surface and they form at a statistical rate through time. A primary impact crater forms when an extraplanetary bollide hits a surface and the energy of impact excavates a crater. This will launch an ejecta blanket, and there can be cohesive blocks of ejecta that are launched as part of it. If those blocks are large enough, they will form their own craters and we call those secondary craters. Secondary craters violate both tenants of crater age-dating because they occur neither randomly with time nor across the surface.

Secondary craters can be separated into two artificial classes - what I call near field and far-field. And I should also mention that I've published on both, and the reason this podcast is two days late getting out is that I'm near the end of writing a grant to fund me to study these in more detail. Near-field secondary craters generally form in a ring around the primary crater and are within about 3 crater diameters of the primary. They look different because they're formed from lower energy impacts, and they're often asymmetric, highly elliptical, and found in chains and clusters.

Far-field secondary craters are usually harder to find and to trace back to a parent primary because, by definition, they're far from their parent. The large, 1000-km Orientale Basin on the moon launched secondary craters over half-way around the planet. I published a paper last year where I identified around 20,000 far-field secondary craters from a 220-km primary on Mars, and these far-field craters were up to 25% of the way around the planet, or around 5000 km.

The issue of secondary craters was first pointed out in the 1960s by Eugene Shoemaker. It was generally ignored by most of the community until the past decade when higher resolution images for many of the solid surfaces in the solar system showed that this is actually a problem that we need to understand.

And it's still hotly debated in the community. One group says that these are a huge problem with smaller craters and that any craters smaller than a kilometer or so can't be used for age-dating because they're likely to be secondaries. Work on Mercury done by people I work with suggests the cut-off there is more like 10 km. The other group says that there's such a pervasive "background field" of secondary craters that these were included in the standard functions we use for assigning absolute model ages, and so we don't have to worry about them 'cause they're already in the counts.

The creationists locked onto two 2005 papers that really set the planetary community on notice that these were an issue we needed to deal with. One paper was by Bierhaus et al. who looked at craters on Jupiter's moon Europa and found evidence that up to 95% of all small craters on the moon were secondaries. The other paper was by McEwen et al. who studied a fresh, young crater named Zunil in one of the youngest areas of Mars and estimated that up to 10 million small - as in, meter-sized - craters surrounding Zunil were secondary craters.

For a quote-mining creationist, this was perfect news to write an article titled, "Crisis in Crater Count Dating." And one did.

But, if you've been following this discussion you'll see that there is NOT a crisis in crater count dating. The issue is that we don't know the level of contamination to what diameter range AT SMALL DIAMETERS. ALL research has shown that on EVERY solid surface with the exception of Mercury, you are quite safe from almost all secondary craters if you are using craters that are larger than about 5 km. Which most people do.

The fine print is that there are always some exceptions; for example, that 1000-km-diameter Orientale Basin on the moon has nearby secondary craters in long chains where each crater is around 20 km across. But, a happy feature of secondary craters is, as I said earlier, they look different from most primary craters, and the Orientale secondaries can easily be excluded from any crater counts by anyone who knows what they're doing.

Disproof: Venus lacks craters.

Something that's discussed even more rarely than craters in creationist writings is Venus craters. As an overview, Venus has very few craters on its surface, though it does have more than Earth. The number is around 1000. Based on our choronology from the moon that I talked about last episode, this mean that Venus' surface is only around 700 million years old. The current thinking is that Venus suffered catastrophic flood volcanism around 700 million years ago because it doesn't have plate tectonics to release heat - it just kept getting hotter and hotter until finally the crust cracked and the planet was resurfaced.

Obviously, 700 million is not 6000. But, there's a deeper problem here. If you want to have a consistent chronology between the moon and Venus, then you have to take the creationist idea of the moon and scale the number of craters forming per time interval UP by a million. Meaning that Venus was completely resurfaced 700 years ago or less.

That raises problems for the formation timescale of a lot of other geologic features that happened after the resurfacing.

A way around THIS for creationists is to argue that Earth and the Moon are, of course, special. That God caused just Earth and the Moon to experience a huge flood of impactors, much as I discussed earlier in this episode. So you then get back to the problem of the chronology for how quickly craters form. It's something of a back-and-forth argument that, in the end, won't really leave anyone happy.

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