How Do Scientists Know?

Those scientists dudes–and dudenas–are so smart! They can tell you how much oxygen a dinosaur was using. They can figure out where the bubonic plague came from, 700 years ago. They can use new computers to rescan old pictures to look for earth-nudging asteroids. Exploring the universe with tools, logic, and an understanding of the behavior of things, they can describe what happened in places they can’t see and have never gone. Knowledge spreads ever-so-slightly outward into the vastness of the unknown.

Drawing of Dr. Jasmina Wiemann’s test subjects from

Strangely enough, it gives me a warm and fuzzy sense of comfort. As the kids say, Science gives you All the Feels. But let’s not get it tangled up with Belief.

Hot Blood Begets Hot Thoughts and Hot Deeds

Whether dinosaurs were hot-blooded or cold-blooded is a century-old argument. It was two whole classes in my semester of Paleontology 2A, back in the 1980s. Dr. Jasmina Wiemann at CalTech may have come across clues that explain why it’s been so hard to determine. The answer is a little of both.

Dinosaurs were reptiles. They lay eggs, and they don’t have fur/hair–I will spare you the much longer explanation involving clades. Modern reptiles are cold-blooded, ectothermic; they rely on external sources to raise body temperature enough to move around. They have slow metabolisms, so are very thrifty with their energy movements. Mammals and other creatures are endothermic or warm-blooded, with fast metabolisms. We can move around even when it’s not warm or sunny, even though we’d rather burrow under the covers. And some of us have such low metabolisms that even thinking about Cheetos causes bloating. But I digress.

It has always seemed confusing to paleobiologists that dinosaurs could be huge predators, fast-moving, while simultaneously being cold-blooded. But how would you evaluate metabolism in a fossil? In decades past, scientists evaluated mineral isotopes in fossil bones, then drew conclusions about the temperatures that were suggested, using bone fragments like “paleo thermometers.” The problem was that they didn’t know if fossilization itself–the bone turning to stone–changed the chemistry. So that process was imperfect.

Metabolic markers left in bone tissue of Allosaurus. Photo from

What Dr. Wiemann and her colleagues did was use a different kind of marker in the bone: signs of metabolic waste. Breathing oxygen triggers a chemical reaction that involves the body’s fat storage and sugar content. Creatures with high metabolisms use fat and sugars differently than those with low metabolisms, leaving behind different waste products. Those chemical waste products are very stable, enough to leave evidence in bone fragments that are 150 million years old.

Wiemann looked at different groups of reptiles: giant sea creatures (plesiosaurs), flying reptiles (pterosaurs), dinosaurs (allosaurs), as well as modern birds, reptiles, and mammals. By comparing markers, she was able to show that most dinosaurs had high metabolic rates and were warm-blooded. This included big predators like the T-Rex but also some large plant eaters, too. Some, like Velociraptors, had zippy metabolisms, almost as high as modern birds, which have some of the highest metabolic rates. Giant herbivores like Brachiosaurus coupled efficient digestive systems with high metabolisms. Their problem was cooling down all that size.

Other dinosaurs, however, developed low metabolic rates, like Triceratops and Stegosaurus even though they may have evolved from ancestors with higher metabolisms. These cold-blooded dinosaurs also developed body armor, horns, and hard-to-attack shapes because they wouldn’t have moved fast enough to outrun the warm-blooded predators. It must have worked because enough grew to adult size for us to find their bones, millennia later. Warm-blooded or cold-blooded? Dinosaurs included some of each.

Flea-ing the Fields

If 150 million years ago seems too long ago to contemplate, then how about 650 years? When I was researching the Black Death a couple months ago for fun, I was surprised that so much was known about the origins of Yersinia pestis, the bacterium that caused the bubonic plague. This was another kind of biological history, also relying on evidence from the past. This time the evidence was microscopic in a different way. It came from the DNA.

From Y. Pestis analysis in Nature Genetics, 2010.

A model like the one above, which describes the movement of Y. pestis over time, required multiple Lego blocks, multiple research studies, to build its foundation. Researchers needed to determine that Y. pestis was the cause of the plague, which they did by looking at the teeth of medieval skeletons. They needed to sequence the Y. pestis DNA: see skeleton teeth. Actually, they also needed to know how to sequence DNA and have big enough computers to do so: see the 1990s.

In 2010, a team of thirty researchers investigated the phylogeny of Y. pestis. The team had to be large and international because samples of the strain are under governmental lock and key, like small pox. They were able to identify the bacterium’s migration and mutation over time by looking at 933 samples and arranging them in sequence, or in order of tiny little variations. They could tell that the original root and several of the key nodes go back to China to the beginning of the Common Era (birth of Christ). But several other key strains also originated in China around 545 to 700 years ago.

From Y. Pestis analysis in Nature Genetics, 2010.

These clusters–namely 2.MED–spread east to west across what is now Siberia into the populated centers. The Black Death of 2.MED ! China lost some 60-80% of its population; Europe 30-70%, depending on whether you were in a city (Florence 80%) or countryside (15%).

Here, researchers built scientific models that string together mutations like individual frames in a projector film. Gather enough frames, and you can run the projector back and forth to see how things happened. Maybe scientists are just like nerdy movie directors, only they do it with data. If you do that with words, then you’re a storyteller. Add music and you’re a bard.

Run the Projector Over a MUCH Wider Area

Meanwhile, THOR is protecting us against asteroids. With Mjollnir, I presume.

Not an asteroid predictor, actually. But could you lift it? Photo of Mjollnir from Marvel cinematic universe fandom.

Actually, it’s not THAT Thor, but a system called Tracklet-less Heliocentric Orbit Recovery, the brainchild of Dr. Mario Juric and Joachim Moeyens at the University of Washington. They developed an algorithm, a computer program, that can identify asteroids among of a very crowded background of celestial objects.

Asteroids that are spotted moving–those which have “Tracklets”–are the typical ones identified. Easy is relative; it takes a long time and many observations to determine that something is moving. But THOR was developed to pick out objects moving that hadn’t been noticeable before. The system can calculate test orbits over a few observations then project additional movements. If guessed correctly, then suddenly something seen as a single blip could be connected from other views and be categorized as an asteroid.

Potential asteroids identified by THOR. Graphic from New York Times.

The project was funded in part by the B612 foundation, named after the asteroid home to the Little Prince, which just warms the cockles of my scientific heart. What’s especially cool, as the recent NYT story pointed out, is that the new science didn’t require a huge new telescope or use new telescope images. Instead, it applied some brain power via a computer algorithm to review existing images to discover potential celestial wanderers. Some of them might turn out to be problems that we’re better off discovering sooner rather than later.

Science comes in so handy! New technology coupled with different ways of looking at things can help understand the past, which in turn help predicts the future. Looking at animal metabolisms or the migration of bacteria on a flea can help us understand the impacts from climate change. Re-viewing old pictures to spot previously unknown objects might help us see where those objects are eventually going. You need data, tools, and new ways of thinking.

I Believe in Data

The illustrious Fandango wondered the other day what the blogosphere thought about people “believing” in certain persistent unscientific ideas, like a flat earth, ghosts, dinosaurs co-existing with humans and so on. The issue with many of those ideas is the lack of data or conflict with existing data. To my mind, we also have to distinguish between knowns and unknowns, between fanciful notions that are counteracted by known facts as opposed to ideas about things for which data is lacking.

As to the first, if you choose to “believe” in an idea that can be disproven by observation, then it’s similar to believing in a story. You like to think the earth is flat, that the earth was created 6000 years ago, or that dinosaurs co-existed with humans? I would love to tell you about Wonder Lesbian, who belonged to a race of superbeings that once ruled the universe, which was all lesbian. These superbeings became bored by their perfection and shifted into a different part of the multiverse, but Wonder Lesbian stayed to design our earth and its environments, playing around with male egos and volcanoes like a child makes mud pies. But because Wonder Lesbian was omnipotent, she erased all memory of her existence. Disprove me if you will! You can’t!

That doesn’t make it true. Believing in things in a story and then using other details from that story (i.e. using the Bible to “prove” other parts of the Bible) doesn’t make the story true. It’s silly to argue with someone who believes a story which is counteracted by data. People sometimes cling to such ideas because it makes them feel more secure. But it’s hard to take seriously enough to generate any kind of debate.

Do you believe in miracles? Sure. From Batwoman #17.

On the other hand, science hasn’t created models that explain everything, for example the afterlife. In order to do that, we’d have to examine data in the afterlife, and we have no system or frame of reference for that. It would be like time running backward or gravity running upward, like us remembering the future. We don’t know how to do that. Even if someone said they had data from the afterlife, how could we verify it? I’m not saying I “believe” in ghosts; it has nothing to do with belief. I’m saying it’s not verifiable.

Maybe we just don’t know how to do it–yet. Germs were once unexplained phenomena. Einstein and others came up with models that explained gravitational anomalies. Others are working on theories where time works differently than in our universe. Perhaps someone will come up with models that explain post-death anomalies. As of now, there isn’t any data to model it. We can’t run a projector or algorithm on data that we can’t collect.

But scientists are pretty darn smart. Maybe they’ll figure out how to do that. Then, we can ask Jacob Marley or Patrick Swayze what it’s all about. But humans and dinosaurs? Fugeddaboutit.

2 Replies to “How Do Scientists Know?”

  1. 👍🏻

    I’m enjoying Prehistoric Planet, appleTV, for which I’m guessing they (the outstanding scientists) know some things and make up others realistically; first episode a couple nights ago. I watched it sort of like a fairytale, or simply from a child’s perspective. I’m appreciating the different perspective or universe, so to speak, for life on this planet.

  2. I didn’t know that some dinosaurs were warm blooded, but after reading this post, it makes sense that not all of them, as I thought, were cold blooded. And thanks for your very interesting response to my provocative question. I still don’t believe there’s an afterlife (or a god, for that matter), but if someday some smart scientists can definitively prove that an afterlife (or a god) does exist, I will consider that it possibly does.

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