Name: The Other Explosion You Should Know About
Uploaded: 2021-05-01T09:35:03.000Z
Duration: 6 min 54 s
Description: VoiceTubeの動画で発音を聞きながら英語表現を覚えよう！学べる英語：

In 1946, a geologist named Reginald Sprigg was working in the Ediacara Hills of southern

Australia when he discovered fossils of what looked kind of like jellyfish.

He wrote up a paper that described his discovery, but soon he ran into a problem.

Not many people took his claims seriously.

That's because Sprigg's little jelly-looking-things were found in a stratum of rock that was more

But at the time, the oldest known fossils of large, complex organisms were only about

540 million years old, dating from that huge profusion of life known as the Cambrian Explosion.

It would take decades for scientists to fully recognize the importance of Sprigg's discovery.

And it turned out, his weird little jelly-things were only the first in a whole slew of exciting

and strange discoveries that, together, would lead experts to realize there was another

explosion of life before the Cambrian Explosion.

Though less famous than the one in the Cambrian, this sudden burst of diversity marked the

dawn of truly complex life on our planet.

It's come to be known as the Avalon Explosion.

Now, evidence of big complex organisms that pre-dated the Cambrian had been found

But Sprigg's strange, soft-bodied fossils marked the first time that a whole community

And that suggested that multicellular life was not only present before the Cambrian Explosion,

but that it was much more elaborate and diverse than anyone thought.

Still, most experts needed more evidence before they'd start rethinking their long-held ideas about

Then, in 1957, another weird fossil was discovered accidentally, by a kid playing in the Charnwood

No one had ever looked for fossils there before, because the rocks were up to 600 million years

old -- way too old for signs of complex life, or so it was thought at the time.

It was several centimeters long and had a clearly organized structure that marked it

And Charnia convinced geologists to start looking for fossils in rocks they had previously

Then, in the 1960s, researchers made a huge find at a place called Mistaken Point on the

There, in rock dated between 560 and 579 million years old, there were not just a few fossils

of big, complex organisms -- there were thousands of them.

OK but, what were all of these Precambrian life forms, exactly?

Well, some of the earliest, and simplest, macro-organisms from this time are known generally

They all generally resemble Charnia, very thin and shaped like the frond of a plant.

But rangeomorphs were definitely not plants -- they lived too deep in the ocean to be

Instead, they held fast to the seafloor and probably absorbed nutrients in the water.

Because, for one thing, they grew in a way that no living animal does.

Rangeomorphs grew by branching fractally -- meaning, they repeated a single basic pattern over

So, if you look at a rangeomorph closely, you'd see that each branch is actually just

And other Precambrian organisms were equally strange, in their own unique and charming

For example, the vast majority of animals today -- including myself for the most part

But some Precambrian organisms -- like Tribrachidium-- had three symmetrical sections that spiraled

And again, there's nothing alive today that grows like this — plant, animal, or otherwise.

So, it's unclear where many of these early organisms fit in our current understanding

Some scientists think that they may have been some type of stem-animals, an ancient lineage

that we modern animals share a common ancestor with.

Other studies have proposed that they're more ancestral to algae, or fungi, or protists

It's even been suggested that these organisms represent an entire, separate kingdom of life

But not all Precambrian life was so alien-looking.

Some organisms, especially those that appeared later, had traits that made them seem distinctly

They were likely the first metazoans — animals with differentiated body plans and specialized

Not only was this bizarre creature probably one of the first cnidarians -- the group that

includes jellies and sea anemones -- it also contains the earliest evidence of muscle-like

But unlike me, it didn't have to bother with leg day.

Then there were the creatures that showed the first evidence of bilateral symmetry,

One of these was Kimberella, a squishy mollusk-like creature that left tell-tale marks in the

These tracks seem to suggest that it dragged some proboscis-like appendage behind it as

And there was Spriggina -- named for Reginald Sprigg.

This long, segmented creature had a crescent-shaped head with evidence of rudimentary sensory

And it's thought by some to be ancestral to the beloved trilobites.

All of these organisms, taken together, revealed to scientists an entire chapter of the history

of life that, until the 20th century, they didn't know existed.

But it wasn't until 2008 that we had a name for it.

That's when a team of paleontologists at Virginia Tech surveyed all of the research

that had gone into these Precambrian fossils, and determined that they represented a specific,

They named it the Avalon Explosion, after the Canadian site that had preserved so much

But, there's still the question of how this profusion of life happened in the first place.