The Bad, Sad, Rad Red Dot

“Was it just my imagination, Kareem, or was there some side action going on in that Africa‑Eurasia nutcracker video?”

“Always the trained observer, eh, Sy? You’re right, India had an interesting life in the same era. Here, let me bring up another Gplates video on Old Reliable. I need to show both sides of the world so I’ll switch from orthographic to Mollweide projection. Aannd I don’t need to go quite as far back, only to about 120 million years. Mmm, yeah, I’ll squeeze in some special markings, give me a sec… There. This slick enough for you?”

India’s 120-million-year journey
rendered using the GPlates system
and configuration data from Müller, et al., 2019,

“Busy, indeed. Care to read out what‑all is happening?”

“Sure. The big thing, of course, is the new ocean opening up around the Mid-Atlantic Rift. Further south, by 120 million years ago Gondwanaland had already calved off South America and Africa so all it had left was Madagascar, India, Australia and the Antarctic.”

“Somehow I’d always thought that Madagascar was tied to southern Africa, but I guess not.”

“Hasn’t been for 175 million years, and back then it was up level with where Kenya and Somalia are now. OK, what caught your eye east of Africa was India zoomin’ on up there three times faster than South America was drifting away from Africa. What I’ve done here, I locked the display onto Antarctica so everything’s moving relative to that even though Antarctica wandered around a bit, too. Then I marked a spot in central India, dialed back to 120 million years ago and started scanning forward by three‑million-year increments. At each step I put an orange dot over my marked spot. The dot sequence shows the subcontinent’s motion up to today. You can see it’s not a straight line and the points aren’t evenly spaced.”

“The uneven spacing and wiggly line say that India didn’t move at constant velocity.”

“Spoken like a true physicist.”

“And like any physicist who sees a velocity change I wonder about the forces that make that happen. That red dot, for instance, why did it break the pattern?”

“The red dot is special because it marks 66 million years ago. Does that date ring a bell with you?”

“Umm … Ah-hah! That was the meteor that killed off the dinosaurs, right?”

“The Chicxulub impactor had a lot to do with it, but that wasn’t the whole story. The dot is already far ahead of where it should have been considering India’s previous vector. Something happened that sped that plate along a good three million years before the meteor hit. We’re pretty sure the something was related to massive continental volcanic activity on India just south of where my dots are. The lava covered half the continent, six hundred thousand square miles. All that molten discharge undoubtedly came along with toxic gases that would have fouled the planet’s atmosphere and troubled the dinosaurs and everything else trying to breathe,”

“And what caused the volcanoes?”

“Really bad luck. There’s an active hotspot, we call it Réunion after the French island that’s on top of it at the moment. India just happened to pass right over the hotspot between 69 and 63 million years ago. The spot’s rising magma punched through the subcontinent’s bedrock, ran all over the place and maybe lubricated the passage. Then along comes the meteor when India’s only halfway across the hotspot. The asteroid doesn’t hit India but where it hits is almost as bad — just off the Mexican coast, almost exactly on the other side of the planet from where India is at the time. Imagine a massive ring of violent earthquakes sweeping around the Earth’s surface and coming to a focus smack in the middle of the volcanoes. That’s my shooting red line, except the shakers really come at India from every direction. The magma outflow rate doubles. Altogether, the discharge finally lays over 1015 metric tons of lava on top of poor India and whatever’s living there at the time.”

“Wow. Talk about your perfect storm.”

“The only good thing to come out of it is all the minerals in the magma left India with incredibly fertile soil.”

“That’s something.”

~~ Rich Olcott


“Kareem, will you ever actually tell me what’s going on with the volcanoes in Italy and Greece and Turkey? And do it quick, I gotta start getting ready for the lunch trade.”

“Eddie, you’re the one who keeps asking the side questions. Sy, I see you’re carrying Old Reliable.”

“I always travel ready for action, Kareem.”

“You got the GPlates system loaded in there? It’s a go‑to tool in our Geophysics lab.”

“Matter of fact, I do, but I’ve not had time to start playing with it. Here, show us what it can do.”

“I’ve got a particular display in mind, give me a minute. <busy‑fingers pause> There. What you’re looking at is Planet Earth as we think it was 195 million years ago.”

“Is that Pangaea?”
 ”Is that Pangaea?”

“Sure is. Most of Earth’s high‑silica slag had sutured together in one big supercontinent that stretched from pole to pole.”

“What’s on Earth’s other side?”

“Mostly a huge ocean, which is why I colored it flat blue. There were probably seamounts and rifts and stuff scattered around the seabottom but all that high‑density low‑silica structure is long gone, shoved below by the continents that rode over it. This is a snapshot at the time when Pangaea was just beginning to come apart — you can see where South America is ripping away from Africa at their southern juncture, and North America’s just started to move off to the west.”

“What’s the difference between the light blue and the darker blue?”

“Good eyes, Eddie, and it’s important. The light blue is the continental shelf.”

“It’s not part of the continent?”

“Oh, it is. The shelf’s the flooded margin, partly ancient consolidated rock and partly sediments that have washed down over the ages. There’s usually a steepish drop‑off from the shelf down to the abyssal bottoms. My hero Wegener is the guy who realized that when you’re putting the jigsaw puzzle together, the shelf is the border you need to pay attention to.”

“What’s the yellow-line kite shape?”

“It ties together some points that’ll help answer Eddie’s Italy‑Greece‑Turkey question. Let me put the video in motion…”

Earth from 195 million years ago to the present
rendered using the GPlates system
and configuration data from Müller, et al., 2019,

“I see you’ve got Africa in the center instead of the usual New World axis.”

“Why not? Anyway it’s convenient for Eddie’s volcanoes. See that fragment at the kite’s eastern corner? I marked it with dark circle. Watch what happened to it about 55 million years ago, and where it went after that.”

“It banged into what’s gonna be Turkey!”

“Mm-hm, and the land crinkled up and that’s the origin of Turkey’s volcano belt that I’ve marked purple. GPlates calls that chunk the Kirsehir plate. No connection with the vulcanism further west.”

“Wait. That little thing is a plate?”

“The definition depends on who you’re talking to and what about. Officially we’ve got cratons, major plates, minor plates, microplates and terranes, but there’s fuzzy lines between them. GPlates ‘plate’ list contains about a thousand chunks that have moved around independently and are big enough to pay attention to.”

“I can see why you called it the Africa‑Eurasia nutcracker, Kareem. It crunches right down on that continental shelf north of Africa.”

“That’s the planet’s oldest bit of seafloor, Sy, maybe 300 million years old, half again older than anywhere else. Maybe the rock got brittle with age, but the collision region’s faults and folds are incredibly complex.”

“It’s a hot mess, HAW!”

“Can’t say you’re wrong, Eddie. Anyway, south and west of Turkey there’s a whole series of trenches where north‑bound seafloor crust dives under south‑bound structures. The sunken material melts, puffs up and pushes up against what’s above it. All of that leaves beaucoodles of weak spots for magma to leak upwards and you get volcanoes throughout the red‑marked area.”

“One thing I get from this, Eddie, is that it’s not one long arc from Italy through Turkey. Kareem’s pointed out two different formation periods, 50 million years apart.”

“I get that, too, Sy. It’s amazing what you can see when you look close.”

“And when hundreds of researchers gather data over two centuries.”

“Thanks, Kareem. Gotta go.”

~~ Rich Olcott

The Tale of The Stripes

“Wait, Kareem, Eurasia and Africa acting like a nutcracker? I thought Africa is moving straight east, away from the Mid‑Atlantic Ridge.”

“Uh-uh, Sy, everything seems to be swinging around eastern Turkey, Africa going northeast—”

“Africa’s moving? How does anybody know that? How does this ‘continental drift‘ even work?”

“Eddie, those are the questions that messed up Alfred Wegener’s reputation.”

<Eddie settles back in his seat> “I can see this is gonna go on for a while.”

“A little bit. Don’t go throwing shade at my man Wegener, Sy. He wrote the standard textbook in meteorology. He was honored as a pioneer in polar weather studies. He even died saving other people during a polar expedition. His book Origins of The Continents And The Oceans went through four editions so it’s not like his proposals were ignored. The old-line geologists weren’t happy because he used evidence from outside their field and besides, they didn’t believe there was a power source big enough to move continents.”

“Evidence from outside the field?!! The nerve!”

“Nuts, huh? Like, <putting up fingers> Meteorology — glacier tracks from what are now tropical areas. Paleontology — fossils of animal and plant species found on multiple continents that are far apart today. Cartography — everyone who’s seen a world map has picked up on how South America almost fits into Africa’s west coast. Wegener showed that the fit’s much better when you work with the continental shelves. Better yet, he showed how all the major land masses could fit together that way into one big supercontinent.”


“Right, except being German he called it der Urkontinent, meaning the original continent. In his day there were well‑documented geological surveys that matched layers and faults between the North American Appalachians and the Caledonian formations in Scotland and Norway. Not even those forced the geologists to buy in until oceanographers in the 1950s came up with new kinds of evidence that sealed the case. Poor Wegener was 25 years dead by then.”

<Eddie sits up in his seat> “OK, everything moves, but how do you know what direction?”

“Magnetic measurements are a prime data source. When magma exits a volcano, its magnetic atoms like iron tend to align with Earth’s magnetic field and get locked that way when the magma freezes to become lava. Measure the magnetism of a good lava field, you know which way was north at the time of eruption. If it’s a continental lava field you can even grab rocks and assay their radioisotopes to date the field. Do that with two related fields and you can work out where the mass was going at the time and how fast it was getting there.”

<Eddie sits forward in his seat> “So what’s the answer to the geologists’ biggest gripe?”

“The power source? We didn’t have a clue until those 1950s oceanographics guys started mapping magnetic fields and comparing them with improved sonar maps of the ocean bottom. We’d long known about seamounts in the middle of the Atlantic, but sonar scans revealed they’re links in a continuous 10000‑mile chain centered on a broad ridge. It’s almost a single 10000‑mile‑long volcano. Meanwhile, magnetometer scans showed a strong signal right over the chain, just as you’d expect for a lava field. What researchers didn’t expect was two parallel sets of magnetic stripes on either side of the ridge. The stripes march all the way to the coasts on either side. That explained everything, almost.”

“Not to me, it doesn’t”

“Oh, I forgot to mention that we already had evidence from continental lava fields that Earth’s magnetic field flips every half‑million years about, and no, we don’t know why that happens, that’s the ‘almost.’ Anyway, each stripe echoes the field direction at the time it froze to make fresh seafloor. Each flip starts a new pair of stripes sliding away. It all fits a model assuming that below the seafloor there’s a 10000‑mile‑long roll of rising magma in the upper mantle. The rolling pushes up to create the ridge, which cracks open at the center to create the volcanoes. Meanwhile the magma diverges to either side and pushes the Americas apart from Africa and Europe.”

“But what about Italy and Greece?”

~~ Rich Olcott

Just Floating Along

Eddie gets impatient. “OK, I get why volcanoes don’t spit metal, but why do they line up like we got across Italy, Greece and Turkey?”

Kareem gets repetitive. “Like I said, tectonics.”

“Sounds like a brand name for fancy fizzy water. What’s that really?”

“Directly it’s a reference to mountain‑building. Really it’s about everything that happens when the continents move around. That starts with light things floating on top of dense things, like a planet’s rocky material floating on the core.”

“Wait, rocks are heavy. Why should they float on anything?”

“Depends on the rock. Pumice floats on water, but it cheats because it’s loaded with bubbles. Most rocks don’t have bubbles, though. I think of them as compact silicon dioxide structures with an optional sprinkling of metal ions. A silicon atom weighs twice as much as an oxygen, but single iron and nickel atoms weigh nearly as much as an entire SiO2 unit. When everything’s all molten, like back when the proto‑planet was being pelted with millions of asteroids and stuff, atoms can move around and dense ones tend to move downward. Light atoms in the way get shoved towards the surface. Geologists call the process differentiation. Anyway, what you wind up with is a hot core of iron, nickel and other heavy atoms. The core’s surrounded by coats of lighter atoms, mostly silicon and oxygen because those were the most common atoms in the gas cloud we started with.”

“Not hydrogen?”

“Hydrogen was there originally, Sy, but many geologists think that the metal‑silicate mishmash was so hot that most hydrogen atoms shot from the mix beyond escape velocity and just sped off. Solar radiation drove them out to where the gas‑giant planets could capture them. The same geologists think the hydrogen we have now came later, as H2O from incoming comets. There’s a lot of argument on the whole issue.”

“That’s all good, Kareem, but when does the tectonics happen?”

“About 4 billion years ago, Eddie, when the asteroid bombardment tapered off. That shut down a major heat energy source so things started to cool off. Each layer cooled off at a different rate. The silica‑rich slag that rose to the surface radiated heat directly to the Universe and formed a solid crust. Meanwhile the metal‑rich layers inside stayed fluid but contracted.”

“Wait, if the inside shrinks but the outside’s a solid it’d crinkle up like a grape going raisin.”

“Absolutely, and some of us think that’s what happened with Mars and maybe Pluto. That crinkle‑up kind of mountain building is called ‘thrust tectonics.’ There’s evidence that Mars now has a ‘tight cap’ structure with a continuous crust that completely envelops the planet. Along with volcanoes and meteor craters, thrust tectonism seems to have been a major landscape driver there.”

“If there’s a tight cap, there ought to be a loose cap.”

“There is, Sy, and we’re standing on it. About 30% of Earth’s surface is continental crust, high in silica and light metals like aluminum. The other 70% is oceanic crust, which is much thinner. It’s also denser because it’s richer in heavier metals like iron. Some people like the theory that Earth once had a tight‑cap crust of continental material, but a catastrophic collision tore off most of it and gave us the Moon. Anyhow, what continental crust we have is in pieces that are loose enough to wander across the surface.”

“This is starting to sound familiar. I bet they bump into each other, right?”

“On-target, Eddie. The big pieces are called plates. The study of ‘plate tectonics‘ is about the ways they collide.”

“Wait, they got different ways to collide?”

“Oh, yes. The simple case is an equal‑density collision, like north-bound India crashing into Asia. The edges of the plates crinkle up to make mountain chains like the Himalayas. More interesting things happen in a different‑density collision. The low‑density continental crust rides up over the high‑density oceanic crust, drives it down into the hot interior where it melts and rises up, burrowing through anything above it to make—”

“Volcanoes! And my Italy‑Greece‑Turkey line—”

“Is probably the leading edge of what may be the planet’s oldest ocean crust, squeezed in by the Eurasia‑Africa nutcracker.”

~~ Rich Olcott

An Italianate Mantle Piece

Eddie has set out some tables in the Acme Building’s atrium in front of his pizza place. Mid‑morning as I walk by he’s sitting at one of them, reading a newspaper. “Morning, Eddie. Ready for walk‑in customers now that things are opening up?”

“I sure hope so, Sy. The building’s still half‑empty ’cause of the work‑from‑homers but I got hopes thanks to folks like you comin’ in.”

“I’ll drop down for lunch later. Don’t see many actual print newspapers these days. What’s in there?”

“Oh, this is the weekly from my cousin in Catania. Etna’s acting up again, as usual.”


“City on the southeast coast of Sicily, about 20 miles away from the volcano. Even with the earthquakes and eruptions Catania’s almost 3000 years old. Funny, in Italy we got Etna and Vesuvius and Stromboli, Greece has Santorini and Methana, there’s a whole bunch strung out through Turkey — wonder why they all line up like that.”

A new voice behind me, but somehow familiar. “Tectonics.”

I turn. It’s the fellow with the dinosaur theory. “Hello, there. I thought you were a paleontologist.”

“Nah, I prefer really old rocks. The Paleontology course was part of my Geology program. You’re Cathleen’s friend Sy, aren’t you?”

“Guilty as charged. If I recall correctly, you’re Kareem who won the Ceremonial Broom?”

“Guilty as charged.”

“Will you guys quit playing games and just answer the question? What’s with those volcanoes?”

“Sorry, Eddie. You know about continental drift, right, that the continents are big slabs that float on top of the Earth’s molten‑metal insides?”

“Sort of, Kareem. Which brings up another question. If the layer underneath is molten metal, how come the volcanoes spit rock instead of metal? Anyway, how do we know it’s not rock all the way down?”

“Go easy on the guy, Eddie, you’re up to three questions already. Let him catch a breath.”

“Thanks, Sy. Last one first — we get a planet’s density from its size and orbit. For Earth it’s about 5.5 megagrams per cubic meter. For comparison, silicate rocks at the surface cluster around 2.7 and iron runs 7.9. Earth is just too heavy to be rock all the way down.”

“Those numbers put Earth almost exactly half-way between rock and iron. That tells me that half the planet’s mass is rocky. Surely the crust isn’t really that thick.”

“You might be surprised, Sy. Remember, volume goes up as the cube of the radius so it doesn’t take much crust thickness to make a large volume. Mind if I use a paper napkin, Eddie?”

“Nah, go ahead.”

“OK, here’s a really simplistic model. Suppose there’s just two layers, core and silicates, and density within each is uniform which means that mass is strictly proportional to volume times density. Let’s guess that core density is twice silicate density. If the core mass is half the planet’s mass, the core radius comes to … 69% of the total and the silicate layer is 1900 kilometers thick. That’s 2/3 of the way down to the bottom of the mantle, Earth’s real middle layer between crust and core. Almost embarrassingly good agreement, considering. Anyway, Eddie, it can’t be rock all the way down and the metallic component is pretty well trapped below megameters of rock. What escapes is the heat that melts the rocks for volcanoes to spit.”

“You started out with metal in the middle of the Earth and then you switched to iron. Which is it and how do you know?”

“It is metallic, mostly iron and nickel. We’ve got four lines of evidence for that. Meteorites are the oldest. Lots of them are stony, but about 6% are a combination of two nickel‑iron alloys. We think those came to us from planetoids that weren’t harvested when the planets were under construction. Second is Earth’s magnetic field, which we think is generated by currents of molten metal deep within the planet. Third is seismic data combined with lab data on how waves travel through different materials at high temperature and pressure. The observed combination’s consistent with a nickel‑iron core. Fourth comes from nuclear theory and astrophysical observation — iron’s by far the most common metallic element in the Universe. Build with what you got.”

“But what about the volcanoes?”

~~ Rich Olcott

Chutes And Landers

From: Robin Feder <>
To: Sy Moire <>
Subj: Questions

Hello again, Mr Moire. Kalif and I have a question. We were talking about falling out of stuff and we wondered how high you have to fall out of to break every bone in your body. We asked our science teacher Mr Higgs and he said it was something that you or Randall Munroe could answer and besides he (Mr Higgs) had to get ready for his next online. Can you tell us? Sincerely, Robin Feder

From: Sy Moire <>
To: Robin Feder <>
Subj: Re: Questions

Hello again, Robin. You do take after your Dad, don’t you? Please give my best to him and to Mr Higgs, who has a massive job. Mr Munroe may already have answered your question somewhere, but I’ll give it a shot.

You’ve assumed that the higher the fall, the harder the hit and the more bones broken. It’s not that simple. Suppose, for instance, that your fall is onto the Moon, whose gravity is 1/6 that of Earth. For any amount of impact, however high the fall would have been on Earth, it’d be six times higher on the Moon. So the answer depends where you’re falling.

But the Moon doesn’t have an atmosphere worth paying attention to. That’s important because atmospheres impose a speed limit, technically known as terminal velocity, that depends on a whole collection of things

  • the Mass of the falling object
  • the local strength of Gravity
  • the Density of the atmosphere
  • the object’s cross‑sectional Area in the direction of fall

The first two produce the downward pull of gravity, the others produce the upward push of air resistance. Fun fact — in Galileo’s “All things fall alike” experiments, he always used spheres in order to cancel the effects of air resistance in his comparisons.

Let’s put some numbers to it. Suppose someone’s at Earth’s “edge of space” 100 kilometers up. From the PE=m·g·h formula for gravitational potential energy and dividing out their mass which I don’t know, they have 9.8×105 joules/kilogram of potential energy relative to Earth’s surface. Now suppose they convert that potential to kinetic energy by falling to the surface with no air resistance. Using KE=m·v² I calculate they’d hit at about 1000 meters/second. But in real life, the terminal velocity of a falling human body is about 55 meters/second.

That Area item is why parachutes work. Make a falling object’s area larger and it’ll have to push aside more air molecules on its way down. Anyone wanting to survive a fall wants as much area as they can get. A parachute’s fabric canopy gives them a huge area and a big help. Parachute drops normally hit at about 5 meters/second. Trained people walk away from that all the time. Mostly.

Which gets to the matter of how you land. Parachute training schools and martial arts dojos give you the same advice — don’t try to stop your fall, just tuck in your chin and twist to convert vertical kinetic energy to rolling motion. Rigid limbs lead to bones breaking, ligaments tearing and joints going out of joint.

So let’s talk bones. Adults have about 210 of them, about 90 fewer than when they were a kid. Bones start out as separate bony patches embedded in cartilage. The patches eventually join together as boney tissue and the cartilage proportion decreases with age. Bottom line — kid bones are bendy, old bones snap more easily. For your question, breaking “every bone in your body” is a bigger challenge if you’re young.

But all bones aren’t equal — some are more vulnerable than others. Sesamoid bones, like the ones at the base of your thumb, are millimeter‑sized and embedded in soft tissue that protects them. The tiny “hammer, anvil and stirrup” ear bones are buried deep in hard bony tissue that protects them, too. Thanks to bones and soft tissues that would absorb nearly all the energy of impact, these small bones are almost invulnerable.

To summarize, no matter how high up from Earth you fall from, you can’t fall fast enough to hit hard enough to break every bone in your body. Be careful anyhow.

Sy Moire.

~~ Rich Olcott

  • Thanks to Xander and Lucas for their input.

Elementary History

<chirp, chirp> “Moire here.”

“Hi, Sy, it’s Susan.”

“Well, hello. Good to hear from you. What’s up?”

“I’m out here on my back porch, fooling around on my laptop. It’s too nice to work in the lab today.”

“I agree with you. I’m outside, too, enjoying the Springtime. What’s your fooling around?”

“I found a discovery date list for all the chemical elements. Guess which element was the first that humanity worked with in pure form?”

“Mmm, I’d say carbon, in charcoal.”

“Nope, it’s copper.”


“Mm-hm. Or maybe gold. They both occur as the raw metal but copper’s more common. There was a Copper Age before the Bronze age. The dates are fuzzy because they depend on what the archaeologists find after site scavengers have been there. I’m sending you the first few rows from the list.

years ago
1Copper (Cu)2910000
2Lead (Pb)826000
3Carbon (C)65750
4Silver (Ag)475000
5Tin (Sn)505000
6Antimony (Sb)515000
7Gold (Au)794500
8Iron (Fe)264000
9Mercury (Hg)803500
10Sulfur (S)162500

“You can win most of them from the right ore with relatively simple processing. It makes sense they’re the ones we got to first.”

“Susan, I’m surprised it took a thousand years to realize you can get sulfur from cinnabar ore at the same time you’re cooking the mercury out of it. I wouldn’t want to be downwind from that process or most of the rest.”

“Sure not. I’ll bet there just wasn’t much interest in sulfur until the alchemists started playing with it. Anyhow, I dumped the element data into a spreadsheet and got some fun facts when I graphed it. Look at this. Eight thousand years for 10 elements through sulfur, then 1800 years of nothing. Arsenic doesn’t show up until the Thirteenth Century when I guess royalty started using it to poison each other. And phosphorus — have you read Neal Stephenson’s Baroque Cycle trilogy?”

“Yes, and I know the episode you’re thinking of, where the hero routed a gang at night by coating himself with glowing phosphorus and bursting out of a cave pretending to be a demon. Stephenson put a lot of words into describing how factories obtained mercury and phosphorus back then.”

“Stephenson puts a lot of words into most everything nerdy. That’s why I enjoy reading him. Oh-ho, now I know how you knew about cinnabar being the source for mercury.”

“Hey, Susan, I don’t only do Physics, but yeah, that was from another Baroque Cycle episode. … Looking at your graph here — things certainly took off at the start of the Eighteenth Century.”

“Yes, indeed. Seventy-four elements, everything that’s not radioactive plus a couple that are. I get a chuckle from cobalt being the first element in that wave after phosphorus. You know the story?”

“What story is that?”

“Seventeenth Century miners kept digging up nasty rocks that emitted poisonous gas when smelted along with the desirable copper and nickel ores. They called the bad stuff kobald Oren, German for ‘goblin ores.’ When a Swedish chemist finally purified the material he simply re-spelled the adjective and called the metal cobalt. I love the linkage with Stephenson’s fictional phosphorus-covered demon.”

“Cute. Why the break between rhenium and technitium?”

“That second wave after 1935 is all radioactives. Funny how the timing paralleled Seaborg’s research career even though he never got involved with technitium, the first artificially-produced element. Imagine being the discoverer of ten different elements.”

“Seaborg practically invented that funny bottom row of the Periodic Table, didn’t he?”

“Oh, yes. Not only did he discover or co-discover more than half of those elements, he was the one who proposed setting off the entire group as Actinides, in parallel with the Lanthanides above them. Oh, that reminds me, I meant to show you the other display I built. You’ve probably never seen one like this.”

“Whoa, you’ve colored each element block by how long we’ve known about it. That’s not the kind of thing you can do with crayons.”

“No, I had to do some programming to get the right tints.”

“What’s the little star for in the middle of the scale?”

“That’s when Mendeleev first proposed the Table, smack in the logarithmic center of my timeline. Don’t you love it?”

~~ Rich Olcott

Rotation, Revolution and The Answer

“Sy, I’m startin’ to think you got nothin’. Al and me, we ask what’s pushing the Moon away from us and you give us angular momentum and energy transfers. C’mon, stop dancin’ around and tell us the answer.”

“Yeah, Sy, gravity pulls things together, right, so how come the Moon doesn’t fall right onto us?”

“Not dancing, Vinnie, just laying some groundwork for you. Newton answered Al’s question — the Moon is falling towards us, but it’s going so fast it overshoots. That’s where momentum comes in, Vinnie. Newton showed that a ball shot from a cannon files further depending on how much momentum it gets from the initial kick. If you give it enough momentum, and set your cannon high enough that the ball doesn’t hit trees or mountains, the ball falls beyond the planet and keeps on falling forever in an elliptical orbit.”

“Forever until it hits the cannon.”

“hahaha, Al. Anyway, the ball achieves orbit by converting its linear momentum to angular momentum with the help of gravity. The angular momentum pretty much defines the orbit. In Newton’s gravity‑determined universe, momentum and position together let you predict everything.”

“Linear and angular momentum work the same way?”

“Mostly. There’s only one kind of linear momentum — straight ahead — but there are two kinds of angular momentum — rotation and revolution.”

“Aw geez, there’s another pair of words I can never keep straight.”

“You and lots of people, Vinnie. They’re synonyms unless you’re talking technicalese. In Physics and Astronomy, rotation with the O gyrates around an object’s own center, like a top or a planet rotating on its axis. Revolution with the E gyrates around some external location, like the planet revolving around its sun. Does that help?”

“Cool, that may come in handy. So Newton’s cannon ball got its umm, revolution angular momentum from linear momentum so where does rotation angular momentum come from?”

“Subtle question, Vinnie, but they’re actually all just momentum. Fair warning, I’m going to avoid a few issues that’d get us too far into the relativity weeds. Let’s just say that momentum is one of those conserved quantities. You can transfer momentum from one object to another and convert between forms of momentum, but you can’t create momentum in an isolated system.”

“That sounds a lot like energy, Sy.”

“You’re right, Al, the two are closely related. Newton thought that momentum was THE conserved quantity and all motion depended on it. His arch‑enemy Leibniz said THE conserved quantity was kinetic energy, which he called vis viva. That disagreement was just one battle in the Newton‑Leibniz war. It took science 200 years to understand the momentum/kinetic energy/potential energy triad.”

“Wait, Sy, I’ve seen NASA steer a rocketship and give it a whole different momentum. I don’t see no conservation.”

“You missed an important word, Vinnie — isolated. Momentum calculations apply to mechanical systems — no inputs of mass or non‑mechanical energy. Chemical or nuclear fuels break that rule and get you into a different game.”

“Ah-hahh, so if the Earth and Moon are isolated…”

“Exactly, and you’re way ahead of me. Like we said, no significant net forces coming from the Sun or Jupiter, so no change to our angular momentum.”

“Hey, wait, guys. Solar power. I know we’ve got a ton of sunlight coming in every day.”

“Not relevant, Al. Even though sunlight heats the Earth, mass and momentum aren’t affected by temperature. Anyhow, we’re finally at the point where I can answer your question.”

“About time.”

“Hush. OK, here’s the chain. Earth rotates beneath the Moon and gets its insides stirred up by the Moon’s gravity. The stirring is kinetic energy extracted from the energy of the Earth‑Moon system. The Moon’s revolution or the Earth’s rotation or both must slow down. Remember the M=m·r·c/t equation for angular momentum? The Earth‑Moon system is isolated so the angular momentum M can’t change but the angular velocity c/t goes down. Something’s got to compensate. The system’s mass m doesn’t change. The only thing that can increase is distance r. There’s your answer, guys — conservation of angular momentum forces the Moon to drift outward.”

“Long way to the answer.”

“To the Moon and back.”

~~ Rich Olcott

Several Big Sloshes

“I call distraction, Sy. You were going to explain how come the Moon’s drifting away from us but you got us into radians and stuff. What’s that got to do with the Moon flying away by dragging a big wave around the Earth?”

“It’s not dragging a localized bulge of water like you’re thinking, Vinnie, nothing like that wave on Miller’s Planet. For that matter, the Miller’s Planet wave had a sharply‑rising front which also doesn’t look like the textbook tidal bulge.”

“There’s a textbook on this stuff?”

“Many, Al. Heavy-duty people have spent a lot of time on tides. Think about all the military and commercial navies that depend on boats being able to leave port and dock on schedule.”

“And not run aground <heh heh>”

“Well, yes, Vinnie. Anyhow, like a lot of pre‑computer Physics, that work was based on a simplified ideal system — a moon orbiting a smooth planet with a world‑covering ocean. Water’s drawn horizontally towards the sub‑lunar points making an egg‑shaped surface and everything’s neat.”

“Probably nothing like real life.”

“Of course. Here’s a video I built from satellite altimetry data. The grey dot is roughly the point underneath the Moon as that day progressed. The red‑to‑blue height scale’s in meters.. Not as neat as theory, is it?”

“Wow, that’s a mess. Looks like the Moon’s pulling water along the Canada‑Alaska coast okay, and the western Pacific starts to get a dome going. But the water never catches up before the Moon’s gone.”

“Hey, Vinnie, look how the tides just go round and round New Zealand. And what’s that, Hudson Bay, it’s a pinwheel.”

“Yeah, and in between Africa and Madagascar it’s completely out of phase from what it oughta be.”

“What you’re looking at is slosh. Once again, reality overwhelms a pretty theory. Each basin has its own preferred set of oscillations. None of them match up with the Moon. But the other thing — “

“Tiny numbers. Everything’s like less than a couple meters, not not a big bulge at all.”

“Bingo, Vinnie. Against Earth’s 6.4‑million‑meter radius, those small chaotic sloshes don’t make for effective energy transfer driving the Moon away from us. That theory’s toast.”

“So what’s doing it?”

“There’s two theories that I know of, and they’re probably both right. The first one is Earth tides — that bump you think of as traveling around the planet, but the bump is rock instead of water.”

“That can’t be a big effect. Rocks don’t bend.”

“On a planetary scale they’re not as solid as you think, Vinnie. The rock crust is brittle and really thin, less than half a percent of Earth’s radius. It floats on molten outer mantle which has the fluidity of tapioca pudding. When that structure gives under stress the crust layer cracks. The seismologists and GPS techs have measured surface motion all over the world. When they analyze the maps, the lunar component accounts for up to a meter of coordinated vertical daily movement. Figure the whole Earth is continually being squeezed and pulled to that extent and you’ve got a lot of energy being expended every 24 hours.”

“How about the other theory?”

“There’s no direct evidence, so far as I know, but it seems reasonable on physical grounds. We’ve got two gyrations going on here, right? The Moon is on a 29½‑day orbit while the Earth rotates about thirty times faster. But the two motions use different frames. The Earth’s spin axis runs through the geometric center of the planet and tilts 23° from its orbit axis. Meanwhile the whole Earth‑Moon system rotates about its barycenter, their common center of gravity, which stays inside the Earth about ¾ of the way moonward from the Earth’s middle. That rotation is about 5° away from Earth’s orbit’s axis. Imagine a molten blob near the barycenter, happily following the Moon in the Earth-Moon frame, but the rest of the planet is saying, ‘No, no, you’re supposed to be moving hundreds of miles an hour in a different direction!‘ If the blob’s the least bit lighter or heavier than its neighbor blobs, inertial forces expend energy to kick it out of there.”

“So we got two ways to transfer energy steady-like.”

“I think so.”

~~ Rich Olcott

Here’s a Different Angle

“OK, Sy, so there’s a bulge on the Moon’s side of the Earth and the Earth rotates but the bulge doesn’t and that makes the Moon’s orbit just a little bigger and you’ve figured out that the energy it took to lift the Moon raised Earth’s temperature by a gazillionth of a degree, I got all that, but you still haven’t told Al and me how the lifting works.”

“You wouldn’t accept it if I just said, ‘The Moon lifts itself by its bootstraps,’ would you?”

“Not for a minute.”

“And you don’t like equations. <sigh> OK, Al, pass over some of those paper napkins.”

“Aw geez, Sy.”

“You guys asked the question and this’ll take diagrams, Al. Ante up. … Thanks. OK, remember the time Cathleen and I caught Vinnie here at Al’s shop playing with a top?”

“Yeah, and he was spraying paper wads all over the place.”

“I wasn’t either, Al, it was the top sending them out with centri–…, some force I can never remember whether it’s centrifugal or centripetal.”

“Centrifugal, Vinnie, –fugal– like fugitive, outward‑escaping force. It’s one of those ‘depends on how you look at itfictitious forces. From where you were sitting, the wads looked like they were flying outward perpendicular to the top’s circle. From a wad’s point of view, it flew in a straight line tangent to the circle. It’s like we have two languages, Room and Rotor. They describe the same phenomena but from different perspectives.”

“Hey, it’s frames again, ain’t it?”

“Newton’s inertial frames? Sort‑of but not quite. Newton’s First Law only holds in the Room frame — no acceleration, motion is measured by distance, objects at rest stay put. Any other object moves in a straight line unless its momentum is changed by a force. You can tackle a problem by considering momentum and force components along separate X and Y axes. Both X and Y components work the same way — push twice as hard in either direction, get twice the acceleration in that direction. Nice rules that the Rotor frame doesn’t play by.”

“I guess not. The middle’s the only place an object can stay put, right?”

“Exactly, Al. Everything else looks like it’s affected by weird, constantly‑varying forces that’re hard to describe in X‑Y terms.”

“So that breaks Newton’s physics?”

“Of course not. We just have to adapt his F=m·a equation (sorry, Vinnie!) to Rotor conditions. For small movements we wind up with two equations. In the strict radial direction it’s still F=m·a where m is mass like we know it, a is acceleration outward or inward, and F is centrifugal or centripetal, depending. Easy. Perpendicular to ‘radial‘ we’ve got ‘angular.’ Things look different there because in that direction motion’s measured by angle but Newton’s Laws are all about distances — speed is distance per time, acceleration is speed change per time and so forth.”

“So what do you do?”

“Use arc length. Distance along an arc is proportional to the angle, and it’s also proportional to the radius of the arc, so just multiply them together.”

“What, like a 45° bend around a 2-foot radius takes 90 feet? That’s just wrong!”

“No question, Al. You have to measure the angle in the right units. Remember the formula for a circle’s circumference?”

“Sure, it’s 2πr.”

“Which tells you that a full turn’s length is times the radius. We can bridge from angle to arc length using rotational units so that a full turn, 360°, is units. We’ll call that unit a radian. Half a circle is π radians. Your 45° angle in radians is π/4 or about ¾ of a radian. You’d need about (¾)×(2) or 1½ feet of whatever to get 45° along that 2-foot arc. Make sense?”

“Gimme a sec … OK, I’m with you.”

“Great. So if angular distance is radius times angle, then angular momentum which is mass times distance per time becomes mass times radius times angle per time.”

“”Hold on, Sy … so if I double the mass I double the momentum just like always, but if something’s spinning I could also double the angular momentum by doubling the radius or spinning it twice as fast?”

“Couldn’t have put it better myself, Vinnie.”

~~ Rich Olcott