Joe McCormick

speaker

4,384 appearances 9 recordings 1 series first heard Sep 2026 last heard yesterday

Joe McCormick’s voice in public audio — every appearance, attributed to the second.

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recordings per month · last 12 months

Recordings per month over the last 12 months — 9 in all, peaking in Sep 2026 with 9.

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Stuff To Blow Your Mind · From the Vault: The Wallace Line, Part 2 · 22 Sep 2026 podcast

Once continuous land masses, allowing land animals to cross freely between them, which is how you end up with large land mammals like tigers and elephants living on what appear to be remote islands. voice-verified

In most cases, they didn't swim there, certainly not in stable breeding populations. voice-verified

They crossed on land at a time when there was a land bridge. voice-verified

And for the most part, voice-verified

Wallace correctly identified that many islands east of the line of the Wallace line were once joined as a single land mass with Australia, this landmass now known as the Paleocontinent Sahul, with islands west of the line once being part of a more continuous landmass, with Asia now known as Sunda. voice-verified

However, just because islands are close to each other does not mean a land bridge always forms between them when sea levels drop. voice-verified

Uh, what Wallace did not know for sure, but lit what later proved perfectly consistent with his observation of the faunal boundary, is that between Bali and Lombok, there is a deep ocean trench. voice-verified

Uh the Strait of Lombok is not wide. voice-verified

Again, it's just a few kilometers wide at the narrowest point, but it is very deep, meaning that even when sea levels were at their voice-verified

at their lowest, a land bridge between the two islands never formed, and thus there was much less opportunity for land-based animals to colonize one island from the other. voice-verified

Uh the reason for the existence of this deep ocean trench, by the way, brings us back once again to plate tectonics. voice-verified

This trench is the meeting point between two plates, where one is undergoing subduction, meaning it's being driven down underneath the other plate at the meeting point. voice-verified

Subduction zones tend to create deep ocean trenches along with other geologic activity like earthquakes and volcanic eruptions. voice-verified

So plate tectonics. voice-verified

Tectonics also it explains that the deep ocean trench that keeps the islands apart and never forming a land bridge. voice-verified

But it plate tectonics also helps explain why there were such different collections of animals on Sunda and Sahool to begin with. voice-verified

They were once separated by much more ocean than they are now. voice-verified

Sahul, and again, this is modern day Australia and New Guinea. voice-verified

And some other associated islands, this was once part of the same land mass as what is now Antarctica. voice-verified

And over tens of millions of years in isolation from the Afro-Eurasian and American land masses, this ancient continent experienced its own distinct branch of evolution, giving us, for example, marsupials instead of the placental mammals that you would find on the rest of the country. voice-verified

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