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Go to Brilliant.org/SciShow to learn how you can take your STEM skills to the next level! [♪ INTRO] If we ever find a way to bring the non-avian dinosaurs back to life, there are probably some species better left as giant ornaments hanging in museum lobbies. Like the Tyrannosaurus rex, the so-called king of the tyrant lizards.

Well, according to a study published this week in Nature Evolutionary Biology, all those T. rex fossils may not actually be what we think they are. There may be at least two other members of this royal family. In your biology class, you may have learned about the systems scientists use to classify living creatures.

For example, humans are called Homo sapiens. The word Homo comes from the Latin for “human,” and that’s our genus, and the sapiens bit is the species within that genus. For a while, as far as we knew, humans had the Homo genus all to ourselves, but then scientists found the remains of extinct species similar enough to join the group, like the Neanderthal.

In other cases, scientists noticed that animals grouped into one big species actually turn out to be pretty different, so they break it up into different species. That’s what happened with giraffes back in 2016. Did you miss that news?

Because instead of just one big group of giraffes, scientists found there were actually four distinct ones. I know. You may have been a little busy in 2016.

I had a child. I wasn’t listening to the giraffe news. And now, it might be the Tyrannosaur’s turn…because the more the merrier, right?

As of right now, the T. rex is the only species recognized in the tyrannosaurus genus. But over the decades, paleontologists have noted that their fossils are pretty diverse. Like some specimens have just one set of long narrow incisors, and others have two.

Also, the size and structure of the femur bones can vary a lot, with some being more stocky and others more slender. Some paleontologists say these are merely differences between males and females. Meanwhile, others argue it has to do with how old a dino was when it died.

But are there enough differences in some of the T. rex fossils to be an entirely different species? One team set out to answer that question by studying about 40 fossils, most of which were excavated from around what is now the Rocky Mountain region in the US. About half of the dinosaurs had femurs to analyze, and it turns out that about two-thirds of them were the robust type.

If the difference was due to sex, they argue that the ratio should have been about 50/50. Also, some of the slender femurs were found in fully grown adults, while some of the robust ones were in larger juveniles, so age didn’t seem to answer the question, either. For twenty-eight of the fossils, the team was able to figure out how long ago they lived, based on how far down in the fossil record they’d been buried.

And while all of the oldest femurs were robust, the slender femurs became more abundant in younger layers of rock. But robust femurs were there, too, which suggests that Tyrannosaurs, at least in this part of the world, grew more diverse over a million years or so. And while only about a dozen fossils could have their dental records compared against their femur bones, there did appear to be a connection between the two.

The ones with more slender femurs were more likely to have one set of incisors instead of two. Now, is this enough evidence to suggest that the tyrannosaur genus evolved from one species into two over time? This team seems to think so.

They do acknowledge that the T. rex could have just come in way more shapes and sizes than might be expected for other species. Still, based on both the differences between fossils, and the differences over time, the team proposed adding two additional species to join the ranks of the T. rex, named T. imperator, and T. regina. T. imperator refers to the O.

G. Tyrannosaurus, which eventually evolved into the rex and the regina species. So you know…why worry about one Tyrannosaurus when you can have three!

I can see the Jurassic Park writers just goin’ for it, right now. They’re very excited. Our next story takes us even further back in time, to before any life existed on Earth at all.

This week in Nature, a team of scientists think that our planet became more habitable thanks to a wet, blob-filled layer of rock deep beneath the surface. Roughly four and a half billion years ago, our baby Earth was a giant ball of molten rock and metal. And because it was molten, different layers were able to separate out, metals sank toward the center to make our core, and light, silicon-rich minerals rose to form our crust.

And in the middle, there’s the mantle, which is made up of denser minerals. Over 500 million years or so, that molten ball of Earth turned into a vacant home. Geologists refer to this period of time as the Hadean eon, in reference to the hellish environment that any foolish time traveler would stumble into if they went then.

During that time, the planet’s atmosphere was mostly a bunch of carbon dioxide and water vapor that had bubbled out of the cooling magma; these greenhouse gasses were thick enough to keep surface temperatures at the current boiling point of water. But scientists estimate that around 4.3 billion years ago, Earth’s crust had solidified, and even managed to create an ocean. By the end of the Hadean, the climate had stabilized, and surface temperatures had mellowed out to levels similar to those today.

In fact, it had mellowed out so much it’s thought that life could have evolved as early as 4 billion years ago. But how exactly was the Earth able to make such a sudden shift, geologically speaking? Well, it’s possible that Earth itself was able to suck that CO2 out of the atmosphere.

So one team from the USA tried to figure out exactly how that could happen. Having a large amount of CO2 in the air means a lot of it is kept dissolved in the oceans…like a pressurized soda can. When that dissolved CO2 reacts with oceanic crust, it can form another carbon-based mineral called carbonate.

And as tectonic plates slide over one another, the newly formed mineral, with CO2 trapped in it, gets delivered back into the mantle. But if the uppermost part of the mantle is too dry and stiff, that tectonic movement can’t happen as fast. So the team proposed that the mantle had to have a special mineral composition.

Small blobs of iron-rich minerals were inconsistently mixed into one layer of the mantle, hanging out with other minerals high in magnesium. That composition would help prevent the creation of that drier, stiffer mantle by stopping it from growing too thick, and thus, it would prevent the slowing down of the crust recycling process. According to their research, this setup could extract the estimated amount of carbon dioxide in that early atmosphere in as little as 160 million years.

But this isn’t all just about removing excess greenhouse gas. This mineral composition can also release hydrogen and methane when it reacts with water. And methane is the simplest of the organic molecules.

It’s thought to have been used by early life to create energy before anything was capable of photosynthesis. So this model helps explain not just how the Earth turned on a geological dime from inhospitable to inhabitable, but offers up a source of fuel for those early Earth inhabitants. And if you want to branch out to models that are set up in modern times, you should check out the course “Computer Science Fundamentals” of today’s sponsor Brilliant.

They are a fully interactive online platform with science, engineering, computer science, and maths courses. And there’s no coding required for the computer science course, so it’s ideal for anyone that wants to learn the ropes or just strengthen their core computer science concepts. To sign up, visit the link in the description or visit Brilliant.org/SciShow to get 20% off the annual Premium subscription; and checking them out also helps us, so thanks! [♪ OUTRO]