You might wonder whether there’s any value in learning about
things that happened millions of years ago.
And maybe there isn’t any value…or maybe there is, at least
in the sense of, if it happened then, maybe it can happen now.
THE BEND IN THE CHAIN
(Image: The line of volcanoes forming the Hawaiian-Emperor Chain. note the 60-degree bend halfway--which has been dated at 47 milliion years ago. Credit: NOAA.)
So there’s the question of the distinct but odd bend in the
Hawaiian-Emperor chain—that series of volcanic mountains that runs from Lo`ihi
and Hawai`i to the southeast, to Detroit Seamount to the northwest—way up by
Kamchatka.
The rocks of the chain have been dated, and the oldest ones--up near Russia--are 80 million years old. At the bend, 47 million. Kaua`i is at about 5 million. And the Big Island is downright new.
The Emperor half of the chain is a series of volcanoes whose
peaks are underwater. The Hawaiian half has peaks mainly above the surface—from
Kure Atoll, through Midway, Pearl and Hermes, Lisianski, Laysan, Maro, Gardner,
French Frigate, Mokumanamana, Nihoa--and then Kaua`i, Ni`ihau and the rest.
If you follow the line of volcanoes from the Hawai`i end to just beyond Kure they take a sharp 60-degree bend to the right.
What’s that about?
A new paper suggests that the bend is pretty clearly the
result of two things, but that one of them—tectonic plate drift—is the main
one.:
One, the whole floor of the Pacific Ocean, which had been
drifting northward, suddenly changed direction 47 million years ago and began
drifting westward.
Two, the volcanic hot spot—which had been piercing the ocean
floor to create volcanoes—was drifting itself, and was drifting generally
southward.
The paper in Nature, written by a team led by Trond Torsvik,
of the University of Oslo, says it’s pretty clear what dynamics are at work.
“While southward
hotspot drift has resulted in more northerly positions of the Emperor Seamounts
as they are observed today, formation of the HEB (Hawaiian-Emperor Bend) cannot be explained without
invoking a prominent change in the direction of Pacific plate motion around 47”
million years ago, the paper says.
It’s pretty clear you need both factors to explain the bend,
Torsvik’s team said.
“After more than two decades debating hotspot drift versus
Pacific plate motion change to explain the HEB, we must realize that neither of
these two end-member options is able to accurately reproduce the geometry and
age progression of the Hawaiian-Emperor Chain.”
THE MORE INTERESTING ISSUE
The paper gets a little testy about the continuing debate,
and says there’s a better place to focus our attention.
“We can stop going in circles and move forward, focusing new
research on understanding the processes that resulted in the change in the
direction of the Pacific plate motion at around 47 Ma, which we conclude is a
prerequisite for explaining the formation of the HEB,” the paper says.
At this point, we know what happened. What we still don’t know is why.
Why did the largest geological feature on the planet—the Pacific
Ocean floor—suddenly change directions. What exactly happened 47 million years
ago that made the Pacific Plate turn its steering wheel right?
There was lots of stuff going on back then.
Australia was in the process of ripping itself away from the
Mainland, a process that started about 45 million years ago.
The massive meteor impact that formed the Chicxulub Crater
was 18 million years earlier.
On the land, there were tiny early mammals that seem lemur-like. A fossil find from the period of the HEB was named Darwinius
masillae--a cute little mammal with a tail.
On both land and sea there were whales that could both swim
and walk on land.
In 2012, a team of researchers collected deep sediment
samples from the Pacific Ocean that were able to track the climate back 53 million years.
It says that the planet was coming off a period of extreme
warming at the beginning of the sample, and cooled right through the 47
million-years-ago period when the Pacific Plate changed directions.
Interesting, but what could that have done to planetary geology?
Or what else was happening on our planet?
Which takes us back to the big question: Why did the Pacific
Plate take its right turn?
And how does that information help us live our lives today?
BACK TO THE LITTLE 47 MILLION YEAR-OLD MAMMAL
This is a diversion, but I was fascinated by that little warm-blooded critter that populated our world at the time of the Hawaiian-Emperor Bend. It was named Darwinius masillae.
The creature had fingers and nails, not claws. It had opposable big toes, like humans and monkeys. It was about two feet long, like a lemur or a big squirrel. It lived near what is now Germany.
Seen here is an image of the fossil, from the American Museum of Natural History.
© Jan TenBruggencate 2017
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