125 million years ago, a swampy forest in what’s  now Lebanon was abuzz with bugs of all kinds.

Mosquitoes and flies filled the air.

Giant,聽 predatory water bugs lurked in the depths,聽聽 while millipedes and cockroaches聽 scuttled along the forest floor.

And on one of the many trees in this聽 dark, dense forest was an unlucky beetle,聽聽 covered in a sticky yellow goo that聽 would eventually harden into amber.

This was a classic case of being聽 in exactly the wrong place,聽聽 at exactly the wrong time – because,  at this point, amber was pretty new.

To date, paleontologists have only found a handful聽聽 of amber deposits older than this聽 poor beetle's final resting place.

But everything was about to change.聽 Suddenly, amber began popping up everywhere,聽聽 entombing animals like insects,聽 lizards, and even ammonites.

This kicked off a period of 54 million years聽 known as the Cretaceous Resinous Interval,聽聽 preserving amber in hundreds聽 of locations across the world.

In Lebanon alone, over 8000 fossil specimens聽聽 have been found from only 10聽 kilograms of studied amber.

It was a gooey, gummy point in聽 Earth's history - and then amber聽聽 suddenly disappeared for another 20 million years.

So we have to ask: what exactly made聽 this time period so very, very sticky?

Now, the process of forming amber is finicky,聽 and it requires a few specific conditions.

The first is that there must聽 be plants that produce resin,聽聽 the gooey stuff that eventually turns into amber.

Resin is a unique substance.

It’s thicker than  sap and isn’t something that all plants can make.

If there’s one group of plants that’s well  known for making resin, it’s the conifers,   which includes things like pine trees,聽 spruces, and monkey puzzle trees.

And although they first showed up during the聽 Carboniferous Period, around 320 million years聽聽 ago, conifers exploded in diversity during the聽 end of the Jurassic and early Cretaceous Periods.

Suddenly, these resin-producing trees dominated聽 the landscape in a way they hadn't before.

So the first condition for聽 amber formation was met:聽聽 there were a lot of trees聽 that could produce resin.

But that alone isn't enough.

Something has to聽 trigger the plant to actually make that resin.

See, trees produce resin in response to injury or聽聽 illness.

It seals over cuts and holes, and聽 is even anti-microbial and anti-fungal.

And of course, it’s also anti-beetle and  anti-insect, since they get encased in it and die.

So resin is less like tree blood and more聽 like… dangerously sticky tree band-aids.

These band-aids are, ultimately,聽 temporary.

As the plant heals,聽聽 the hardening resin plug is pushed聽 out in a process called pitching out,聽聽 effectively removing any infection聽 or unlucky insect along the way.

Then, for the resin to turn into amber,聽 it can't just linger above the ground.聽聽 Most resin decays or burns - in order聽 to fossilize and change into amber,聽聽 it needs to be covered in sediment and preserved.

So to create amber, you need to hurt the right聽 type of tree and bury its discarded band-aids.

But even then, preservation of amber is still聽 rare.

So, to produce the vast amber deposits聽聽 of the Cretaceous Resinous Interval,聽 you would need to injure whole forests.

So who, or what, was hurting all these trees?

One potential suspect is, well, the planet.

The Cretaceous Period was very warm,聽 with high levels of carbon dioxide聽聽 that trapped solar energy.

All that extra聽 energy may have caused extra hurricanes,聽聽 which uproot trees, remove their聽 leaves, and even snap off whole limbs.

And that sort of damage can cause trees聽 to produce a lot of resin in response.

But the world wasn't just warm -聽 the atmosphere also had more oxygen聽聽 than it does today.

Which means聽 there were a lot more wildfires.

And the trees that survived these fires聽 didn't do so unscathed.

To heal themselves,聽聽 they would have produced large amounts of resin.

But though it certainly contributed,聽聽 scientists don't think that the climate alone聽 was responsible for the resinous interval.

That's because the resinous interval has another聽 strange pattern - it seems to have been聽聽 regional and patchy, and most of these patches聽 have been found in the Northern hemisphere.

See, high oxygen and carbon dioxide are聽 global problems - if they were the sole cause,聽聽 we should find a ton of resin across the globe.

A pattern of damage in only part聽 of the planet suggests the trees聽聽 were being injured by something more local.

Which brings us back to that seemingly innocent聽 beetle.

Or, technically, some of its relatives.

These are some of the oldest聽 known members of the Scolytinae,聽聽 commonly called bark beetles.

Today,聽 there are over 6000 described species.

And some bark beetles have such a specialized聽聽 set of adaptations that they've earned聽 themselves the name ambrosia beetles.

They eat only ambrosia fungus, which they聽 farm themselves by burrowing into trees聽聽 and planting the fungal spores聽 on the walls of their tunnels.

The beetles even tend to their crops by聽 weeding out competing fungi and bacteria.

And when it's time for ambrosia beetles聽 to move on and establish a new colony,聽聽 they bring their fungal gardens with them.

Ambrosia beetles have evolved special pockets聽 or divots on their bodies called mycangia,聽聽 which are humidity- and temperature-controlled,聽 to keep fungal spores alive between homes.

Which is great for the beetles…but not for  the trees.

Ambrosia fungus is one of a tree's聽聽 worst enemies.

For them, it's a terrible聽 parasite that spreads throughout the wood.

Infected trees may wilt, have stunted growth,聽聽 or even die.

And of course, in response to聽 this infection, those trees release resin.

For years, paleontologists suspected that this聽 was the cause of the Cretaceous Resinous Interval:聽聽 damage from ambrosia fungus,聽 spread by diligent beetle farmers.

But in this last decade, we've realized that聽 can't be true for a few different reasons.

The first is that those ancient beetles probably聽聽 didn't have the close relationship with聽 fungi that their descendants do today.

It's not clear exactly when farming evolved,聽 but mycangia and other physical adaptations聽聽 only seem to have evolved around 54 million聽 years ago, long after the end of the Cretaceous.

The other problem is that when聽 you look at Cretaceous amber,聽聽 you find very few members of Scolytinae.聽 So even if they were farming fungus earlier聽聽 than expected, they simply weren't聽 abundant enough to be responsible.

Which brings us back again to聽 that beetle trapped in amber.聽聽 It seems that for years this poor聽 beetle's family was framed… but by who?

Thanks to the work of paleontologists聽 and entomologists, we now suspect聽聽 someone else.

A cousin of sorts…one with  its own relationship to ambrosia fungus.

These are the ship timber beetles, which are in聽 a totally different family from the bark beetles,聽聽 and are named for their annoying habit聽 of putting holes in the sides of ships.

Of course, in the absence of ships, these聽 beetles were perfectly happy to bore into trees.

But just boring into wood is more annoying聽 for trees than devastating.

And adult ship聽聽 timber beetles only bore into wood聽 so that they can deposit their eggs.

The larvae live in the wood,聽 but the adults fly away.

The fungus can often end up in those bore holes,聽 too, which scientists initially thought was聽聽 just an accidental infection – with the fungus  taking advantage of the holes bored by larvae.

So…wouldn’t that make ship timber beetles  just like bark beetles?

Innocent bystanders聽聽 in the battle between Cretaceous trees and聽 whatever was causing them to produce resin?

Well, no.

See, adult ship timber beetles actually聽 leave something else behind along with their eggs:聽聽 the spores of fungi and yeast, which they聽 carry in a special slot on their abdomen.

And these become a feast of聽 ambrosia fungus for their larvae,聽聽 even though they don’t farm it  the way ambrosia beetles do.

In fact, this may be how the relationship聽 between the ambrosia beetles and their聽聽 fungi first evolved, with an accidental聽 benefit soon turning into full agriculture.

But the realization that the mothers are聽 deliberately introducing the fungus, makes聽聽 it more likely it was ship timber beetles that聽 were actually behind the spread of the fungus.

They weren’t bystanders,  but instead disease vectors.

And unlike ambrosia beetles, ship timber聽 beetles are far more common in Cretaceous amber.

So paleontologists originally had the聽 right fungus, but the wrong beetle.

While research is always ongoing,聽聽 it seems for the moment that we've聽 identified the Cretaceous culprit.

Yet… both ambrosia and ship timber  beetles are still around today,聽聽 and the Cretaceous Resinous Interval聽 stopped in, well, the Cretaceous.

So聽聽 why didn’t it – and the accompanying  spike in amber preservation – continue?

Well, like we said before, amber聽 is finicky.

You have to have a lot聽聽 of different factors all working together聽 in order to preserve large amounts of it,聽聽 and beetle infestations are only one of many.

The warm climate and high oxygen levels聽 of the Cretaceous weren't around forever.聽聽 And as the climate changed, so did the forests.

New plants began to evolve, developing聽 flowers and seeds, outcompeting the old聽聽 conifer forests.

Entire families of conifers聽 went extinct or became a lot less abundant.

Amber does still periodically show up in聽 the fossil record after the Cretaceous,聽聽 but not quite to the same extent.

Instead, there are occasional big deposits,聽聽 like the Eocene Baltic amber or the聽 Miocene amber of the Dominican Republic.

And of course resin is still around today - we聽聽 even farm it ourselves to use in聽 things like varnish and incense.

But as it is, the perfect storm of聽 climate, evolution and environment聽聽 that created the Cretaceous Resinous聽 Interval eventually came to an end.

And so, too, did its massive,聽 widespread amber deposits.

There are still patches of amber through time,聽聽 but nothing like the gooey聽 golden forests of the Cretaceous.