Why Do Tornadoes Suck Things Up?

My six-year-old nephew spent the weekend at my house, which delighted my son to no end. The end result was the sort of excited chaos you might expect – lots of six-year-old bickering, and toys strewn everywhere, and strange non sequitur laced conversations. At one point, tornadoes came up. I don’t know why, because I wasn’t paying attention to the start of that conversation. But my nephew declared that he’d seen a tornado, and that his mom had made them get in the closet. And my son responded that you didn’t get in the closet, you got in the tub, because we’d had a tornado warning once and our front bathroom is the safest place in our condo for that sort of thing. So they argue the merits of bathroom versus closet for a few minutes, and then my son looks at me. I smile, preparing my “it depends on the house” explanation for the question I’m sure is coming.

“Dad?” my son asks. “Why do tornadoes suck things up?”

All right. So that isn’t the question I expected.

What is a tornado?

The National Oceanic and Atmospheric Administration has a page titled The Online Tornado FAQ, and I’ll be referencing it a lot over the course of this question. To begin with, I’ll just quote their answer to the question:

According to the Glossary of Meteorology (AMS 2000), a tornado is “a violently rotating column of air, pendant from a cumuliform cloud or underneath a cumuliform cloud, and often (but not always) visible as a funnel cloud.” Literally, in order for a vortex to be classified as a tornado, it must be in contact with the ground and the cloud base. Weather scientists haven’t found it so simple in practice, however, to classify and define tornadoes (per this essay by Doswell). For example, the difference is unclear between an strong mesocyclone (parent thunderstorm circulation) on the ground, and a large, weak tornado. There is also disagreement as to whether separate ground contacts of the same funnel constitute separate tornadoes. Meteorologists also can disagree on precisely defining large, intense, messy multivortex circulations, such as the El Reno tornado of 2013, compared to the parent mesocyclone and surrounding winds of damaging intensity. It is well-known that a tornado may not have a visible funnel. Mobile radars also have showed that tornadoes often extend outside an existing, visible funnel. At what wind speed of the cloud-to-ground vortex does a tornado begin? How close must two or more different tornadic circulations become to qualify as a one multiple-vortex tornado, instead of separate tornadoes? There are no firm answers.

In other words, a tornado is a vortex, very much like an atmospheric whirlpool. In an oversimplified fashion they form under basically the same conditions – our atmosphere is described by the same fluid dynamics that describes the behavior of water, after all. Moving air hits a barrier – in this case, denser colder air – and twists back on itself. The air is still moving into the barrier, however, so the air that is deflected back picks up speed thanks to the conservation of angular momentum, creating a vortex.

But, like I said, that’s the oversimplified explanation. Here’s what NOAA says on the subject:

The truth is that we don’t fully understand. The most destructive and deadly tornadoes occur from supercells–which are rotating thunderstorms with a well-defined radar circulation called a mesocyclone. [Supercells can also produce damaging hail, severe non-tornadic winds, unusually frequent lightning, and flash floods.] Tornado formation is believed to be dictated mainly by things which happen on the storm scale, in and around the mesocyclone. Recent theories and results from the VORTEX programs suggest that once a mesocyclone is underway, tornado development is related to temperature changes across the edge of downdraft air wrapping around the mesocyclone (the occlusion downdraft). Mathematical modeling studies of tornado formation also indicate that it can happen without such temperature patterns; and in fact, very little temperature variation was observed near some of the most destructive tornadoes in history on 3 May 1999. The details behind these theories are given in several of the Scientific References accompanying this FAQ

What this means is that they’re vortices, and they form just like any other vortex. But, like most things in nature, they’re super complicated and we don’t really quite understand what makes them start.

So how do these tornados suck things up?

The famous “sucking tornados” are “multiple vortex tornados“, and they create what is called a “suction vortex“. Interestingly, the suction vortex has little to do with air pressure, and everything to do with wind speed. That is, the lower air pressure within the vortex isn’t low enough to “suck” things up. Tornadoes aren’t straws. Instead, the speed of the winds traveling up the vortex funnel create the “suction” effect.

Here’s what happens. The secondary vortices of a multiple-vortex tornado orbit the axis of the primary vortex, increasing the wind speed around the primary vortex. When the wind from and around the secondary vortices “turns the corner” – that is, enters the primary vortex and suddenly changes from horizontal to vertical flow – angular conservation causes the wind to pick up an enormous amount of speed. It is this wind speed that lifts objects – cows, trucks, people, roofs, whatever – and hurls them into the air. Note that all tornadoes have this “turn the corner” effect, but it takes the secondary vortices to really get the wind moving fast enough to lift really heavy objects.

Waterspouts and fire tornadoes

My son had heard of waterspouts, and guessed that they were water tornadoes. He was right. A waterspout is literally just a tornado that forms over water and that sucks up water.

Fire tornadoes are a little different. They are similar to actual tornadoes in appearance – except, you know, for the fire – but are formed by rising surface winds (usually generated by the heat from the fire) that meet turbulent winds to form a spiral of rising flame. They aren’t formed by supercell thunderstorms and aren’t tornadoes. Doesn’t make them safe, mind.

 

How Many Spiders?

I’ve been sick for a few days now, so I haven’t put any real time into the “what are these fossils” article I promised last time. Instead, let’s look at something comparatively simple. I picked up my son from Kindergarten yesterday. Normally, since I was home and it’s only about a quarter mile, we’d have walked. But, like I said, I’ve been sick. So he’s in the back seat excitedly telling me about his Valentine’s Day party. “Dad?” he asks as we pull into our garage.

“Yes, son?” I respond.

“How many spiders can you carry?”

No, I have no idea where that came from. But I’ve gotten used to that by now. “Well,” I say, “that depends on how big they are, and how cooperative they are.”

So, how many could you carry?

“I could carry a hundred spiders!” he declares.

“Maybe,” I tell him. “If you could put them in a box. Or if they were tiny and well-trained.”

So, how many could you carry? Like I said, it depends on the spider. The good people at Guinness World Records say the Patu marplesi is the smallest spider, while Wikipedia contradicts them and states that a related species – the Patu digua is the smallest. Either way, it’s a tiny spider – the body size is only 0.37 mm – and the author of Catalog of Organisms states that “If one of these spiders crawled into your ear while you were sleeping, it could probably slip into your Eustachian tubes and tap on the back of your eyeballs.” So try not to think too hard about that.

patu-digua

“Peek-a-boo!”

I couldn’t find anything at all about how much (little?) this critter weighs. So, I’m going to run the risk of estimating. Here’s what I did, so that you can play the home game. I found an article titled “Estimating Live Spider Weight Using Preserved Specimens” from The Journal of Arachnology in 1996. It provides a formula for calculating weight from length for spiders: ln weight = 1.844 + 2.711(ln length), and seems to indicate that the weight is read in milligrams (mg) and the length in millimeters (mm). So, that would give us ln weight = -1.844 + 2.711(ln 0.37). That works out to… let’s see…

  1. ln weight = -1.844 + 2.711(ln 0.37)
  2. ln weight = -1.844 + -2.695
  3. ln weight = -4.539
  4. e^ln weight = e^-4.539
  5. weight = 0.010684 mg

So, one 0.37 mm spider appears to weigh 0.01 mg. How many of these could we move? Let’s find out?

Bare Hands

My palm is, roughly speaking, a 9 cm by 9 cm (90 mm by 90 mm) square. That gives me 8,100 mm of surface area, so I could stack a single layer of 8,100/0.37 = 21,891 well behaved Patu digua on one hand. Using both hands, I could carry 43,782 of them. The two-hand load would come out to 0.43782 grams, or 0.0015 ounces of spider.

Let’s try and do more. If I cup my hands, I get a sort of rounded cone that’s 7 cm (70 mm) in diameter by 7 cm (70 mm) deep. That gives me a volume of 359,189 cubic mm. Now, let’s assume that the Patu digua takes up the same volume as a sphere 0.37 mm in diameter. That’s 0.212175 cubic mm. So, in my cupped hands, I could carry 359,189/0.212175 = 1,692,890 Patu digua. Those guys would weigh in at 18.0868 grams (0.63799 ounces).

We’re not savages, you know

Yes, I know. So let’s fill a box. A standard U-Haul shipping box is 41.5″ (1054.1 mm) x 38.5″ (977.9 mm) x 18.75″ (476.25), for a volume of 429,072,327.3375 cubic mm. That means I could carry 429,072,327.3375/0.212175 = 202,256,756 of the little spiders – 21.606 kg (47.6 pounds) of Patu digua. My son weighs more than that, so I know for a fact that I could easily carry that box of spiders from my house to my car, and then from the car to the Post Office, and then from the Post Office back to my car because the USPS would most likely refuse to accept that package.

Cool. What about big spiders?

National Geographic informs me that the South African Goliath Birdeater Tarantula is the biggest spider in the world as measured by body size. Nothing I could find gave me an explicit size, but terms like “puppy sized” and “the size of a dinner plate” were bandied about with distressing familiarity. National Geographic also states that:

Many of the locals in northeastern South America regard T. blondi as a tasty snack. They first singe off the urticating hairs, then wrap the spider in banana leaves to roast it. Tarantula expert Rick West, who once sat down for a meal of these spiders with the local Piaroa people of Amazonas in Venezuela, says T. blondi can be surprisingly tasty and moist. (Also see “UN Urges Eating Insects; 8 Popular Bugs to Try.”)

“The white muscle ‘meat’ tastes like smoky prawns, while the gooey abdominal contents is hard-boiled in a rolled leaf and tastes gritty and bitter,” West says. “The three-quarter-inch [two-centimeter] fangs are used after the meal as toothpicks to remove T. blondi exocuticle from between one’s teeth.”

goliath

“I’m tasty!”

On the other hand, if you’re measuring by legspan the prize goes to the giant huntsman spider, with a leg span over one foot (30.48 cm) across. No word on how they taste, though.

huntsman

“Come on and have a go, if you think you’re hard enough!”

Without specifics, I can’t tell you how many I could handle. One per hand, maybe, and maybe four in a shipping crate. But, on the other hand?  Oh my god no.

What Is A Fossil?

A couple of days ago the weather was nice enough that I walked to my son’s kindergarten to pick him up. As we walked home, he declared that he was “collecting nature” and picked stuff up. Pine cones (which he rejected after a minute as being “squishy”) and sticks, things like that. Oh, and a rock. He picked up a largish, flat rock that got him asking if we could eat off a stone one day. “People used to do that,” he assured me. “Can we?”

“Maybe,” I told him, turning the stone over in my hands. He’d asked me to carry it, so he could climb a retaining wall. “But we’ll have to clean it well first.” Then something caught my eye. “Hey, look,” I said. “Fossils!”


His eyes went big, and he scrambled over to see what I was talking about. Impressions of shells in the stone. “My first fossil!” he declared, taking the stone back. “I found my first fossil!” And suddenly, he had to carry the stone, and he told me he wanted to get a paint brush out.

“Why?” I asked, puzzled.

“That’s what paleontologists use to clean stones!” he told me.

At the end, we settled on using an old toothbrush of his to scrub the dirt away. And that is how we found the thing that will be at least two entries for this blog.

What is a fossil?

If you’re reading a blog like this, you probably have a passing familiarity with what a fossil is. If nothing else, you’ll be thinking about dinosaur bones that have turned to stone and then been dug up and assembled to display in a museum. A fairly succinct definition of the word comes from Biology Online, which states:

noun, plural: fossils

(1) Any preserved evidence of life from a past geological age, such as the impressions and remains of organisms embedded in stratified rocks.

(2) The mineralized remains of an animal or plant.

adjective

Having the characteristic, or pertaining to the nature, of a fossil.

Supplement

Fossils include shells, imprints, burrows, coprolites and organically-produced chemicals. The oldest fossils were bacteria that existed 3.8 billion years old. Fossils are once thought of to be all from extinct species until some were found to belong to species that are still living.

Word origin: from Latin fossilus, (something dug up)

In other words, fossils aren’t just bones, and they aren’t even necessarily pieces of living things. The Sam Noble Museum in Oklahoma follows what appears to be a common practice of breaking fossils into three broad categories: body fossils, molds and casts, and trace fossils.

  • Body Fossils are what you usually think of when you think of a fossil, the fossilized remains of an organism (or part of an organism). Usually, it’s just the bones or other hard parts of the animal because the soft tissues rot and/or get eaten.
  • Molds and casts are a type of body fossil, but they aren’t directly the remains of the organism. A mold is rock that has formed around the body fossil, making an imprint of the fossil’s shape. A cast is what you get if new rock forms in that mold, or more commonly if sand or mud fills the inside of a hollow structure (such as a shell) and becomes rock. Interestingly, sometimes you get molds of the soft tissues of the dead animal. When found, these allow insight into what the animal’s skin was like.
  • Trace fossils are indirect signs of a creature, such as footprints or coprolites (fossilized waste) or burrows or nests.

How Do Fossils Form?

I’ll be honest, and tell you right here and now that I’d assumed that there was a whopping one single way that fossils form. The classic “bones get covered and minerals slowly leach into them over time, replacing the calcium in the bone” routine you probably learned about in elementary school (or, if you’re like me, from reading a ton of dinosaur books in kindergarten). This is certainly one way to do it, but it isn’t the only way. The most common methods are petrification and carbonization, but there are most certainly others.

Petrification is the most common variety of fossilization, and (as you might guess) it’s the classic “bone or shell to stone” form of fossilization. It comes in at least two forms, replacement and permineralization.
replacemnet-fossil-galleryimage

  • Replacement is the best known of the best known methods, because it’s the one you always hear about. Water dissolves the original hard structures, replacing them with different mineral matter. What kind of mineral matter depends on the mineral content of the water, but calcite, silica, pyrite, and hematite are most common.
  • Permineralization happens when ground water infiltrates microscopic pores and cavities in the hard structure, depositing minerals. This results in a fossil that still has much of the original hard material left behind, mingled with the deposited mineral.

Carbonization is a form of fossilization most commonly found in plants, although animal can do it as well. Under the right conditions the organic substances of the organism decay but the carbon in the organic molecules is left behind in the shape of the fossilized structure.
carbonized-fossil

There’s also a few types of fossil that you might not think of as “fossils”, because they don’t turn to stone. Plants and animals trapped in amber are fossils, for instance. So are the animals that got trapped in tar pits (La Brea being the famous example here in the United States), and the animals that froze and then freeze-dried in the Arctic (such as mammoths). They’re still preserved evidence of life, even though they didn’t turn to stone.

So, that’s a really high level look at fossils. Tune in next time, when we try to work out what fossils he has. Because trust me, my son has been asking.

Who Was The First Person?

That was the question my son asked, from the back seat of my wife’s car. I don’t remember the context, but I think we were talking about his grandparents. Things my dad had done, things my wife’s father had done, sharing family stories. That sort of thing. And then he asked it. “Who was the first person?”

That is a hard, heavy question.

What is a “person”?

Merriam-Webster gives multiple definitions for the word “person”:

  1. human, individual —sometimes used in combination especially by those who prefer to avoid man in compounds applicable to both sexes <chairperson> <spokesperson>
  2. a character or part in or as if in a play : guise
  3. a : one of the three modes of being in the Trinitarian Godhead as understood by Christians; b : the unitary personality of Christ that unites the divine and human natures
  4. a archaic : bodily appearance; b : the body of a human being; also : the body and clothing <unlawful search of the person>
  5. the personality of a human being : self
  6. one (as a human being, a partnership, or a corporation) that is recognized by law as the subject of rights and duties
  7. reference of a segment of discourse to the speaker, to one spoken to, or to one spoken of as indicated by means of certain pronouns or in many languages by verb inflection

For these purposes, we’ll focus on the first definition: “human, individual”. Which shouldn’t be a surprise, as it’s pretty clear from the context that my son’s question should be understood as “who was the first human”.

Human beings are formally known Homo sapiens, with contemporary human beings classified in the subspecies Homo sapiens sapiens – a rather arrogant sounding name, since it means “Wise wise man” when translated from Latin. We are part of family Hominidae (also known as “great apes”), a family that includes Homo (us), Pongo (orangutans), Gorilla (gorillas, go figure), and Pan (chimpanzees). Hominidae is part of the Primates, which is an order of the class Mammalia. At present we are, arguably, the most successful branch of both Primates and Hominidae, as we have a globe-spanning range of habitation. We’re certainly the most successful current branch of Homo, as we’re the only extant branch of that genus.

primate-cladogram-2_med

Our family tree

So, who was the first Homo sapiens?

This is where things get tricky, because “species” is a difficult concept to pin down. You’re probably familiar with some version of Mayr’s Biological Species Concept, which defines a species as “groups of actually or potentially interbreeding natural populations, which are reproductively isolated from other such groups”. The problem with this definition, and this is a problem biologists are well aware of, is that nature is “squishy”. Not all species reproduce sexually, for instance. Does that mean they aren’t a species because this concept doesn’t apply? If two different species can successfully breed, even if they wouldn’t normally do so in the wild, does that make them different speices because they’re usually reproductively isolated or does it make them the same species because they can still produce viable offspring? The answer is the subject of a lot of arguments among biologists.

This “squishiness” combines with evolution to make it impossible to pin down a “first” Homo sapiens, or even to say for certain what was H. sapiens and what was a different Homo species. The Neanderthals, for instance, were Homo neanderthalensis, a different species from Homo sapiens, but there is enough genetic evidence to make an argument that they certainly weren’t reproductively isolated from our species. The jury is still out on that, but given some of the other things humans will do today it’s certainly not unreasonable to assume that our ancient ancestors were open to having sex with another species of Homo.

All we can say for certain is that our species differentiated itself from our direct ancestor species – Homo erectus (“upright man” – somewhere between 1.8 million years ago and 200,000 years ago. Which means that we likely overlapped with H. erectus for a significant amount of time, as the oldest fossils of H. erectus are around 1.9 million years old and the youngest are around 70,000 years old. So, worst case, we overlapped with H. erectus by some 130,000 years, which is significantly longer than recorded human history. But we can certainly speculate. There wouldn’t have been a sharp dividing line between H. erectus and H. sapiens, and certainly no moment where a H. erectus mother looked at her baby and said something like “hey, this is different“, because evolution doesn’t work like that.

The lineage that gave rise to H. sapiens would likely just have started off as just another subspecies of H. erectus, like H. erectus erectus (“Java man”), H. erectus nankinensis (“Nanjinj man”) or H. erectus georgicus. That subspecies would have been somewhat geographically and/or culturally isolated from its neighbors – although possibly still indulging in the occasional opportunistic “gene swapping opportunity” – until, over time, it became different enough that it became a distinct organism. Could the new archaic H. sapiens have successfully interbred with H. erectus at that point? Possibly. We could have interbred with H. neanderthalensis, after all. But since all we have left of H. erectus is fossil bones, we’ll probably never know for sure.

That said, genetic studies have indicated that there is something approximating a “first” human man and a “first” human woman.

It’s fun to stay at the MRCA!

MRCA is the Most Recent Common Ancestor, and it’s exactly what it sounds like: the most recent individual from which all members of a set group are descended. For you and your siblings (if you have any), your MRCA is your father and mother. For you and all of your cousins on your mother’s side of the family, your MRCA is your maternal grandparents. And so on. Generally speaking, the larger the group the further back you have to go to get a MRCA. Also, the paternal and maternal MRCA need not always have lived at the same time. Imagine yourself as having a half-brother because one of your parents divorced and remarried. YOu might share a father with the half-brother, making your father the paternal MRCA for that group. But you might have to go back dozens of generations to find a maternal MRCA.

The maternal MRCA for all of H. sapiens is nicknamed the Mitochondrial Eve, and she lived in Africa quite some time ago. How long? well, depending on the type of analysis applied, it could be as long ago as 234,000 years ago or as recently as 99,000 years ago. I won’t pretend to understand the details of how that was calculated, beyond the simple statement that it has to do with mutation rates in mitochondrial DNA – the DNA of the little organelles that our cells use to convert oxygen and sugar into energy. I’m a stockbroker, after all. Not a geneticist or cell biologist.

Our paternal MRCA has been nicknames the Y-chromosomal Adam, and is currently estimated to have lived around 200,000 years ago. Also in Africa, so there is a slim possibility that our paternal and maternal MRCAs knew each other. Don’t count on it, though.