In 2017, a team of scientists  reported a strange discovery   deep in the bamboo forests of  Anji county in Eastern China.

Sections of a layer of mudstone 10 meters thick  were spread across 10 kilometers of the forest.

This had once been a deep-water ecosystem,   some 445 million years ago, right  at the end of the Ordovician period.

And it’s one of the few fossil sites that shows  us the direct aftermath of the first - and   one of the worst - mass extinctions  that the planet has ever experienced.

But to the surprise of the researchers,   this site didn’t paint a picture  of an apocalyptic wasteland… Instead, it preserved the remains  of a thriving and diverse community:   thousands of big, complex animals that  seemed to have been living their best lives.

And those animals were almost entirely sponges.

Hidden in the forest, the researchers  had discovered a piece of a weird,   but critical time in the deep past… A time when the first-ever mass extinction may  have turned Planet Earth into Sponge World.

The end of the Ordovician period was  a pretty terrible time to be alive.

I don't know if you remember it,  but... when you get to be my age... Complex animal life in the oceans  was still in its early days, having   only really taken off in the Cambrian  period right before the Ordovician.

But just when the age of complex  life had entered full swing,   it was very nearly snuffed out entirely by  the first of the Big Five mass extinctions.

Now, we don't know exactly what caused  the Late Ordovician mass extinction,   but we have a few hypotheses ranging from  potentially reasonable to kind of out-there.

These include drastic shifts in climate  and changes in ocean oxygen levels,   volcanism, and even gamma  ray bursts from deep space.

Whatever the cause though, the extinction event   lasted around 2 to 5 million years and  wiped out around 85% of marine species.

This makes it one of the most  severe mass extinctions in history,   second only to the Great Dying at the end of  the Permian, around 200 million years later.

And the devastation hit all  sorts of early animal groups   pretty hard, including trilobites,  brachiopods, corals, and bryozoans.

And it was assumed that sponges had  fared no better than anyone else.

They’re an ancient phylum of animals that  live simple, quiet lives as filter-feeders   attached to surfaces underwater,  unable to move much as adults.

And until recently, basically  no complete fossil sponges had   been found in layers from the mass  extinction or its direct aftermath.

In 2015 though, researchers in China  reported the first evidence that at   least some sponge communities  had made it through just fine.

They found fossils of around 35 species  of sponges from the Ordovician-Silurian   boundary in Anhui province in South China,  belonging to a bunch of different lineages.

This was unexpected, and their explanation -  which seemed reasonable at the time - was that   this might’ve been a unique exception to the  wider state of ecosystems during this period.

These sponges must have represented an  unusual group that had been forced into   shallow waters due to a sudden lack of oxygen in  the deeper oceans during the extinction event.

They were essentially a band of  initially lucky survivors that   had been fossilized while trying  to flee the environmental chaos.

Insofar as sponges can flee anything...

But the discovery of the Anji biota in that  bamboo forest two years later showed that   this wasn't just a unique and isolated  group of desperate spongy survivors… Because the Anji community, located  around 100 kilometers away from Anhui,   contained an even more diverse group of  sponges with over twice as many species!

And, like the Anhui biota, those species  belonged to many different sponge lineages.

This is important because it showed  that they weren't the result of   a sudden radiation of sponges from a few  surviving lineages after the mass extinction.

Instead, the diversity of  these species suggested that,   while whole other branches of the  tree of life were withering away,   the sponge branch seemed to have not even noticed  that there was a mass extinction going on at all.

In fact, the Anji sponges from immediately after   the mass extinction were at least as  diverse as modern sponges are today!

Aside from the more than 2000  individual sponges though,   the number and diversity of the  other fossils in the Anji layers   are more in line with what you’d expect  immediately after a mass extinction… These included graptolites, four nautiloid shells,   and a single sea scorpion.

Not  exactly a thriving ecosystem.

And the next year, in 2018, researchers  added even more sites to this rapidly   growing pattern of sponge-dominance  in the aftermath of the extinction.

They reported seven new, similar sites across  2000 kilometers of what's now South China.

It was a continuous and hyperdiverse  mega-community of sponges flourishing   all over the place during a period of  mass death for basically everything else.

And the researchers argued that this was  probably not just a regional sponge paradise.

They proposed that the same thing was probably  happening in similar environments elsewhere,   turning much of the planet into Sponge World.

It’s just that not everywhere had the right   geological conditions to preserve  clear evidence of Sponge World,   and we hadn’t specifically been searching for  that evidence until just the last few years.

So what was going on here?!

Why did sponges survive and flourish while almost   everything else had either succumbed to  the devastation or was barely hanging on?

It just hardly seems fair.

Like, if you told me that sharks or fungi  or vultures or maggots love a good mass   extinction and thrive on biological carnage,  I'd be like “well sure, good for them."

But sponges?

Those colorful, tube-y  things that just sit there looking pretty?

They’re the group that flourished  during an ecological apocalypse??

Well, turns out the answer may be yes:  sponges soak up mass death like a, um… you know, don't make me say it... See, sponges have a few things going for them that   might have allowed them to thrive and  dominate in the post-extinction world… For one, they’re unusually  good at tolerating changes   in temperature and oxygen levels, as animals go.

And these two kinds of changes are  often associated with mass extinctions,   including, we think, the end-Ordovician.

Plus, they get their food by filtering  organic particles from the water,   which would have suddenly increased during the  extinction as organisms died all around them.

It’s also thought that changes on land  associated with the event - like the   melting of glaciers and flooding of  low lying areas - would have led to   a global influx of nutrients from  sediment flowing into the oceans.

And, seeing as so many other  complex food webs had collapsed,   those nutrients that sponges would’ve  usually had to compete with other   species for were suddenly available  in abundance, like iron for example.

Put all these factors together and boom,  you’ve got yourself a sponge world.

And it may not have been a  single, one-off event either.

See, lots of sponge remains have been  reported from other layers directly after   later extinctions, too - including the Late  Devonian crisis around 370 million years ago,   and the End Triassic extinction  around 200 million years ago.

While their level of preservation isn't as  good as the end-Ordovician sponges from China,   they hint at a similar pattern of temporary  sponge dominance following mass extinctions.

And I should add, in all of these cases, the shape  of the pants of these sponges remains unknown.

Did ANY of you think I was gonna get through this  episode without making a Spongebob joke?

Anyone?

We’ve even seen something like this in modern  oceans following recent El Nino events that   disrupt marine ecology.

For a little while  at least, sponges become unusually abundant.

So, sponges becoming ridiculously  successful may in fact be a general   symptom of ecological collapse  both in the deep past and today.

And something we could even be setting  ourselves up for in the future.

But Sponge World might be crucial  for ecological recovery, too.

See, while it may seem like sponges  have a pretty inactive life,   they’re actually ecosystem engineers.

They help stabilize sediment  on the seafloor and provide   a structure for ecosystems to develop around them.

Lots of other groups that were struggling  to recover from major losses during the mass   extinction would have found the abundance of  sponges very useful to attach themselves to.

Others would have found the stabilized  sediment maintained by the sponges to   be a safe and secure habitat to hide out in.

And by forming megacommunities, sponges would  have concentrated organic matter into those areas,   providing localized resources for  food webs to re-establish themselves.

And this may help explain why some  other animal groups also recovered   fairly quickly from the extinction  event after being hit hard initially.

They, and we, may owe the survival of our  lineages through the end-Ordovician to sponges,   and the paradise they built out of the  wreckage of the first ever mass extinction.