Thursday, June 15, 2017

The bend in the Hawaiian-Emperor Chain--we know it happened, but why?

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

Saturday, June 10, 2017

How to tell if an extinct Hawaiian bird was flightless: now there's a tool.

A lot of the early birds of Hawaii were believed flightless due to big bodies and small wings, but until now there hasn’t been a real good way to measure.

(Image:  The fossil bones of Ptaiochen pau otherwise known as a small-billed moa nalo—a big duck that looks more like a goose. Bones like these could be used to determine whether the bird could fly. Credit: Junya Watanabe.)

Today, using a new system developed by Japanese researcher Junya Watanabe of Kyoto University, we can be far more confident that the moa nalo and other big extinct ducks and geese had given up flight in these islands that lacked a lot of the predators of continents.

Helen James, an expert in Hawaiian fossil birds, said Watanabe’s work, published in the journal Auk: Orinthological Advances, said Watanabe’s work is a big step forward.

"Dr. Watanabe has developed a valuable statistical tool for evaluating whether a bird was capable of powered flight or not, based on measurements of the lengths of only four different long bones. His method at present applies to waterfowl, but it could be extended to other bird groups like the rails," said James, Curator of Birds at the Smithsonian Institution's National Museum of Natural History.

Many times, fossil birds must be described from only a few bones, and Watanabe’s method provides a new tool for learning more about them.

"Other researchers will appreciate that he offers a way to assess limb proportions even in fossil species where the bones of individual birds have become disassociated from each other. 

"Disassociation of skeletons in fossil sites has been a persistent barrier to these types of sophisticated statistical analyses, and Dr. Watanabe has taken an important step towards overcoming that problem," James said.

Watanabe studied hundreds of skeletons of relatives of ducks, including both flightless and known not-flighted species. And developed a methodical assessment using such data as the size of leg bones, size of wing bones, body size and an assessment of pectoral muscle development from the keel or breastbone.

In part, Watanabe said, the work was challenging because ducks are so different.

"What is interesting in fossil flightless anatids is their great diversity; they inhabited remote islands and continental margins, some of them were specialized for underwater diving and others for grazing, and some were rather gigantic while others were diminutive."

His paper, "Quantitative discrimination of flightlessness in fossil Anatidae from skeletal proportions" is here

Eurekalert's report on the paper, from which the quotations in this report were taken, is here. 

© Jan TenBruggencate 2017