NOVA; To the Moon; Interview with Graham Ryder, Geologist and Lunar Scientist, part 2 of 2

Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till Till The Highlands, which really should be taken to mean the entire crust not counting the lava planes that are on top of it, were formed rather early for the

most part in lunar history. And it seems as if it must have been a massive system that formed them, a massive silicate melt system that formed them, because they consist to a large extent of the one mineral plagioclase, which is a calcium aluminum phase, and it appears that these must have floated to the top because it's a very lightweight mineral of a large system. We don't see the other stuff that would have crystallized from that melt, which must have crystallized from that melt. And so it appears that it's a flotation mechanism to create the original crust. After that, the moon cooled down a little, but then the interior re-melted, and more stuff came out of the interior and was added to the crust into the crust, as well as perhaps on top of the crust over the next couple of a hundred million years. And so it's not a simple, one-stage process that produced the Highlands, but a complicated set of events over a period of 200, 300 million years. And then, of course, during that time, there was

substantial impacting, or some impacting, which churned the crust up a little bit. But amazingly, despite the battered look of the crust at the moment, the Highlands actually seemed to have preserved quite a bit of the original stratigraphy, the original layering, or different rocks in different places that it originally had, as we can now tell by the data that we have from the Clementine mission, and that we're probably going to improve by looking more at the Prospector mission data. Let's talk about the individual Apollo missions. Is there a way that you can fairly quickly sum up? Did each one contribute its own special awareness? Yes, each mission was planned very much to go to a different kind of site, rather than, except for the first two, which were both oriented towards a nice flat, safe surface to land on. But they turned out to go to somewhat different kinds of basalt types, or the Maury basalt. Those first two landed on the flat Maury basalt plains, but they were different kinds of Maury

basalt. And so they told us quite a bit different about what was happening inside the moon. But subsequently, the missions went to very different Highlands sorts of places. Apollo 14 mission to the Emberium blanket, the debris blanket from the large Emberium impact that occurred. The Apollo 15 mission right onto the edge of the Emberium basin, but it also collected yet another kind of Maury basalt. The Apollo 16 site was on the deep highlands as much as you could get it on the front side of the moon. So it was quite different. And then at Apollo 17, it went to the rim of yet another basin. So the six missions really gave us quite a diverse collection of sites and rocks to work with. It wasn't as if we went to the same place six times, almost. It was nothing like that. Any anything stand out in your mind about those last four that actually went to geologically significant areas? I mean, in terms of did a particular mission yield a particular conclusion or awareness. That's a complicated one actually. You can think about some of the past conferences. Okay. Okay, individual missions

and findings from them. The Apollo 15 mission brought back samples which confirmed the hypothesis very strongly that the Highlands consisted of this Plagiclase-rich rock type, which had been guessed that pretty much from the Apollo 11 and even the Apollo 12 site, but not much from the 14 site. There wasn't so much of that very felt spathic material there. But at Apollo 15, samples brought back which were of that rock type. And when Apollo 16 landed, then those sorts of rock were fairly common among the samples brought back. So it was obvious that that original idea of a Plagiclase-rich crust was in fact correct. There was no doubt about it. That was a fundamental break, I think, in understanding the moon. You confirmed that this crust really existed in the way that we thought it did. I got the sense this morning that the Kona conference was also a fundamental break in understanding the moon, or at least there

was more acceptance in terms of origins of this cataclysmic beginning. You were there, right? Yeah. Did you sense that that was a watershed event in studying the moon? Yes, it definitely was. And it was not because there was any new data or specific data at that time that came along. It was a sort of mindset. Everybody had come to realize 10 years, more than 10 years after the last Apollo mission, that there was old ideas for understanding the moon's origin, the capture, the co-occretion, the fission, just didn't work for what he knew about the moon. And at the same time, there were new ideas of what was happening in the entire solar system, basically, about how planets were built that sort of gel together to produce this giant impact model, which had been proposed earlier, but nobody had paid any attention to it whatsoever hardly. And then at Kona, it just all came together, and people started to be exposed to this and realizing that it fitted a lot of stuff. Now, I'm not sure that that still holds, because there are a lot of problems with that now, that not everything

does fit. There's so much that we don't understand. But Kona, yes, was a different thing. And partly, it was because people were now willing to spend more time thinking about the origin of the moon, whereas during the Apollo days, people were still just basically studying samples and trying to get as much information out of them as possible. But those samples are mainly formed in a period way after the origin of the moon. So by 1984, people were able to sit back and look at the whole thing with some new sorts of information in mind, plus more computing ability was available at that time, so that people could model some of this stuff numerically, which wasn't able to have been done before. Was there a real sense of excitement at Kona in 1984? Oh, I think there very definitely was a sense of excitement that something was different, and that we had made some kind of a breakthrough that we'd gotten out of this idea that there were only three concepts for the origin of the moon at least. And at least now, we had a fourth, which was at least as valid as

those three. And actually, at that time, at least, seemed to make a lot more sense that it worked. Okay, Monterey, 98. Now, you sound not so sure. Well, things develop, and people really try to hammer at a thesis, a theory that hypothesis that comes up, try to figure out if it fits everything, and now there are lots of things, which we don't understand. I'm not saying that they prove that their idea is wrong, but it's obviously there's a lot of work to be done to make sure that we understand that things fit. And it's very difficult because we're obviously looking at something which we can never, ever really check. Nobody was there. A lot of the evidence has been reworked and destroyed. It's like trying to find out what's behind a painting. You just can't see. You peel off so many layers, but ultimately you can't always see what was there. And so we don't know how to approach some of this, but there are many things that we don't seem to fit right now in some respect.

Oh, specifically, you told me. I mean, you say, I'm coming away from this conference here today with a lot more doubt. And why? One of the things which would seem to happen with the origin of the moon by a giant impact is that the earth should melt at the same time because the impact was so big. And yet, the earth does not show real evidence that it ever did go through that stage of totally melting. Despite the fact that it has a big metal core, it's not clear that it did. There's quite a bit of evidence that suggests that it didn't. And some of that has been gone into at this conference. And so that's a problem. Another problem is that the dynamical model suggests now that the giant impact didn't take place when the moon was, when the earth was completely made, but when it was partly made. And so you still have to accrete stuff onto the earth after that. If you do that, you accrete stuff onto the moon as well. And that's an even bigger problem because we don't see any evidence that that happened. The moon does not seem to have accreted

the sorts of things that would have accreted to the earth after that time, after it formed. And so there are one or two holes to say the least. In fact, there are dozens so holes. But we will probably work them out one way or the other before too long, or at least some of them. Great. Great that you're doing. Yes, please. Tell me about the laser dating on the sample. The dating technique that I am part of a team of, the actual work is done by Brent Darryl. That actual work is done by Brent Darryl. And the technique involves radiogenic isotopes of potassium, which decays to produce argon. And all rocks, when they melt, pretty much get rid of any old argon that they have in them. But they retain the potassium that was in the melt as they solidify. That potassium then starts to break down to produce argon. So basically it's a method of measuring the ratio of potassium to argon in the rock, specific isotopes of those

elements. And using that to figure out how long that process has been taking place, which then gives you the age of the rock. With large impacts, you produce a melt, a silicate melt, which degasses the old argon and produces a nice solid rock with no argon in it, or very little. And then the argon is produced by a radioactive decay. The laser argon technique involves neutron activations. And it becomes an argon argon technique in actual fact. And the laser technique is used to, you can use very small samples of rock less than a millimeter in size. And the laser heats that sample. To give off the argon, of which the isotopes are measured. With that technique, we can get ages that are very, very precise. So it's that Brent has managed to date the serantatus impact event to within about 20 million years, at over 3.8 billion years ago. So it's a very, very accurate technique. I know I asked you before, but again, you seem to believe that there's a need

to go back to the moon. And I'd like to hear that. Apollo only went to six land insights, and we have some meteorites from unknown places. But that is barely enough to understand any planet. Many people think that the moon is fairly simple, but it isn't. All the sites that we went to had something different to offer. I'm fairly sure that if we go to other sites, there will be more to offer. But we also have some specific targets in mind. Apollo managed to produce lots of ideas in it.