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  • [ intro ] In a way, humans are part of the one percent.

  • The one percent of species that hasn't gone extinct... yet, that is.

  • There have been five major extinction events on our planet

  • which, combined, have wiped out at least 99 percent

  • of all species that have ever lived.

  • Lucky for us, humans weren't around during any of them.

  • Because, well, there's a decent chance

  • we wouldn't have survived if we were.

  • But, obviously, some animals did make it through.

  • In fact, some animals,

  • like jellyfish and comb jellies, have weathered all five.

  • And that may be thanks to the weird thing they have in common:

  • their jelliness.

  • The main difference between gelatinous animals and the rest of us is water content.

  • Most creatures, including humans,

  • are 60 to 70 percent water.

  • But animals that are consideredgelatinous

  • are 95 percent water or more.

  • And there's no doubt that being that gooey has its perks.

  • After all, gelatinous bodies have independently evolved

  • in almost every major phylum of animals

  • from protists to chordates.

  • And gooeyness might explain why species like jellies survived mass extinctions

  • when most other creatures didn't.

  • For example, during the late Devonian around 360 million years ago,

  • roughly three-quarters of Earth's species disappeared.

  • Many experts think pulses of low oxygen

  • or hypoxic events

  • were a big part of that, especially in oceans.

  • Which makes sense, because oxygen is kind of important

  • especially for animals.

  • For the past 800 million years or so,

  • we've been pretty dependent on the stuff.

  • But gelatinous animals can tolerate lower oxygen levels

  • than us firmer creatures.

  • In part, that's because they literally don't breathe.

  • They just soak up oxygen from their surroundings.

  • Because they're overwhelmingly made of water, O2

  • can diffuse directly from the water around them into the water inside them.

  • So there's no need for dedicated respiratory structures like gills, lungs, or noses.

  • They don't even need blood to shuttle oxygen around.

  • And that means they need less oxygen overall,

  • because those complex tissues require a bunch of it to function well.

  • Jellies are also able to store oxygen inside their structural goo,

  • or mesoglea.

  • So basically, they have a reserve tank that can help them make it through temporary oxygen

  • outages.

  • Of course, hypoxic events aren't the only thing animals have to survive during an extinction.

  • Sudden rises in seawater acidity have also been to blame for a lot of mass death.

  • These tend to be tied to pulses of volcanic activity,

  • because when volcanoes erupt,

  • they spew carbon dioxide

  • a lot of which ends up in the water.

  • And dissolved CO2 reacts with seawater to make it more acidic.

  • Acidification can also happen without volcanoes.

  • Like, that big asteroid that wiped out non-avian dinosaurs about 66 million years ago?

  • Researchers think it vaporized a bunch of sulfur-rich rocks.

  • That led to acidic rains, which caused the ocean's pH to plummet.

  • But whatever the cause,

  • acidification is a huge problem for lots of marine animals.

  • See, the chemical reactions that drive acidification

  • also reduce the number of carbonate ions in seawater

  • ions that many species need to build their shells or skeletons.

  • So in acidic waters, carbonate shells and skeletons dissolve or cost more to construct.

  • And that makes creatures like corals and clams extremely sensitive

  • to even the smallest changes in pH.

  • Even animals that don't build carbonate body parts

  • like fish

  • can struggle as seawater pH drops,

  • because the extra acid messes with their blood chemistry.

  • But acidification isn't such a big deal if you don't have blood or carbonate parts.

  • Some jellies, for instance, can grow and reproduce in extremely acidic conditions.

  • The low pH doesn't seem to bother them.

  • Finally, just in case acidification and hypoxia weren't hard enough to survive,

  • extinction events also tend to mean less food is available.

  • Because, you know, lots of things die.

  • That's kind of the definition of a mass extinction.

  • And that means anything still living has less to eat.

  • It turns out even that is not as big a problem if you're gooey.

  • One of the main reasons animals eat is to obtain carbon:

  • an essential molecular building block.

  • Gelatinous bodies contain very little carbon to begin with,

  • so their food demands are much lower.

  • Plus, when you're gooey, you can really maximize your food intake,

  • because every little morsel in the water sticks to your mucusy feeding parts!

  • Also, thanks to being mostly water, gelatinous creatures are close to neutrally buoyant

  • so, they don't really sink or float.

  • And that means they don't need to exert much energy to swim.

  • So basically, it seems like, if you're made of goo,

  • nothing can take you down.

  • Which might explain why gelatinous organisms

  • have outlasted everything from trilobites to T. rex.

  • And they might make it through the next extinction crisis, too

  • the one happening right now because of us.

  • We're already seeing signs of extreme biodiversity loss,

  • especially in the ocean.

  • So, there's less food to go around.

  • On top of that,

  • the nutrients in our sewage and spilling out from our farmlands

  • are driving massive blooms of algae

  • which use up the available oxygen in their waters

  • leading to huge, hypoxic dead zones.

  • And at least one quarter of the carbon dioxide that we put into the atmosphere from burning

  • fossil fuels

  • is absorbed by our oceans.

  • In fact, in the past 200 years, our oceans have become 30 percent more acidic!

  • So basically: less food, oxygen shortages,

  • and acidification are becoming the new normal in our seas.

  • And that means being made of goo might be more useful than ever.

  • [Optional: I, for one, welcome our gelatinous overlords.]

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  • [ outro ]

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