Scientists discover elusive secret of how continents formed

Scientists discover elusive secret of how continents formed
Esteban Gazel, a geoscientist at Virginia Tech, collects samples of lava in a variety of locations, in this case Etna, Italy, to probe the chemical evolution of the planet. Credit: Virginia Tech

An international research team, led by a Virginia Tech geoscientist, has revealed information about how continents were generated on Earth more than 2.5 billion years ago—and how those processes have continued within the last 70 million years to profoundly affect the planet's life and climate.

Published online today in Nature Geoscience, the study details how relatively recent geologic events—volcanic activity 10 million years ago in what is now Panama and Costa Rica—hold the secrets of the extreme continent-building that took place billions of years earlier.

The discovery provides new understanding about the formation of the Earth's —masses of buoyant rock rich with silica, a compound that combines silicon and oxygen.

"Without continental crust, the whole planet would be covered with water," said Esteban Gazel, an assistant professor of geology with Virginia Tech's College of Science. "Most terrestrial planets in the solar system have basaltic crusts similar to Earth's oceanic crust, but the continental masses—areas of buoyant, thick silicic crust—are a unique characteristic of Earth."

The continental mass of the planet formed in the Archaean Eon, about 2.5 billion years ago. The Earth was three times hotter, volcanic activity was considerably higher, and life was probably very limited.

Many scientists think that all of the planet's continental crust was generated during this time in Earth's history, and the material continually recycles through collisions of tectonic plates on the outermost shell of the planet.

But the new research shows "juvenile" continental crust has been produced throughout Earth's history.

"Whether the Earth has been recycling all of its continental crust has always been the big mystery," Gazel said. "We were able to use the formation of the Central America land bridge as a natural laboratory to understand how continents formed, and we discovered while the massive production of continental crust that took place during the Archaean is no longer the norm, there are exceptions that produce 'juvenile' continental crust."

The researchers used geochemical and geophysical data to reconstruct the evolution what is now Costa Rica and Panama, which was generated when two oceanic plates collided and melted iron- and magnesium-rich oceanic crust over the past 70 million years, Gazel said.

Melting of the originally produced what today are the Galapagos islands, reproducing Achaean-like conditions to provide the "missing ingredient" in the generation of continental crust.

The researchers discovered the geochemical signature of erupted lavas reached continental crust-like composition about 10 million years ago. They tested the material and observed seismic waves traveling through the crust at velocities closer to the ones observed in continental crust worldwide.

Additionally, the researchers provided a global survey of volcanoes from oceanic arcs, where two oceanic plates interact. The western Aleutian Islands and the Iwo-Jima segment of the Izu-Bonin islands of are some other examples of juvenile continental crust that has formed recently, the researchers said.

"This is an interesting paper that makes the case that andesitic melts inferred to derive ultimately by melting of subducted slabs in some modern arcs are a good match for the composition of the average continental crust," said Roberta L. Rudnick, a Distinguished University Professor and chair of the Department of Geology at the University of Maryland, who was not involved in conducting the research. "The authors focus primarily on Central America, but incorporate global data to strengthen their case that slab melting is important in unusual conditions of modern continent generation—and probably in the past."

The study raises questions about the global impact newly generated continental crust has had over the ages, and the role it has played in the evolution of not just continents, but life itself.

For example, the formation of the Central American land bridge resulted in the closure of the seaway, which changed how the ocean circulated, separated marine species, and had a powerful impact on the climate on the planet.

"We've revealed a major unknown in the evolution of our planet," said Gazel, who was the senior and corresponding author of the study.


Explore further

Questions of continental crust

More information: Continental crust generated in oceanic arcs, Nature Geoscience 8, 321–327 (2015) DOI: 10.1038/ngeo2392
Journal information: Nature Geoscience

Provided by Virginia Tech
Citation: Scientists discover elusive secret of how continents formed (2015, March 31) retrieved 17 October 2019 from https://phys.org/news/2015-03-scientists-elusive-secret-continents.html
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Mar 31, 2015
Most scientists are acutely aware of just how much there is yet to know. But just because the last page of the book is yet to be written doesn't mean the pages we're writing now aren't exceedingly important or groundbreaking.

The idea that continental crust is actively produced instead of merely recycled could dramatically change how we do future geology.

Mar 31, 2015
The idea that continental crust is actively produced instead of merely recycled could dramatically change how we do future geology.
Instead of, or in addition to? I don't see anything in this article to suggest it's not a combination.

Mar 31, 2015
"instead of merely" I meant to imply in addition to.

Mar 31, 2015
The formation of the continents is something most of us take for granite....

Mar 31, 2015
Geological change is primarily driven by celestial mechanics.

Mar 31, 2015
@jeffreyjoemiller I would like to meet, JUST ONCE, a) a psychologist that wasn't batshit crazy, or b) a guy with a goatee that isn't a sociopath. I guess your wisdumb comes from covering both bases. Who happens to live in a bowl of granola. Only phrase for SoCal. Wot's not fruits and nuts is flakes!

Mar 31, 2015
Per the article all they did was analysis some volcanoes which have crustal lava compositions from they believe the melting of prior subducted continental edges. I fail to see this work as either revolutionary or revealing as everything they found is already known.

Mar 31, 2015
Per the article all they did was analysis some volcanoes which have crustal lava compositions from they believe the melting of prior subducted continental edges. I fail to see this work as either revolutionary or revealing as everything they found is already known.


"Whether the Earth has been recycling all of its continental crust has always been the big mystery," Gazel said. "We were able to use the formation of the Central America land bridge as a natural laboratory to understand how continents formed, and we discovered while the massive production of continental crust that took place during the Archaean is no longer the norm, there are exceptions that produce 'juvenile' continental crust."

Read more at: http://phys.org/n...html#jCp


Mar 31, 2015
From the article above, I am struggling to understand what is new to these geoscientists w.r.t. tectonic theory. Isn't the recycling of crustal material always our understanding the way the process works? Some of the continental material always gets scraped down melts forming granitic bodies and rhyolitic magmas. Eventually every bit of continental material goes through this process. Eventually all oceanic material does too. Is this new? Has the group added a new wrinkle, excuse the pun, to the process?

Mar 31, 2015
First, the interior of Earth was not three times hotter. In the earlier stages, komatiites were given out by volcanoes; that does not happen now because the interior has cooled, and, as I understand it, by roughly 200 Centigrade degrees sine about 4 Gy BP. The formation of continents relies on the fact that silica, and more importantly, aluminosilicates, have a relative density of about 2.5 - 3, while the olivine/pyroxene groups that comprise basalts have a density of about 3 - 3.5. Light floats on heavy.

The real question is, why did the feldsic/granitic material separate out on Earth to give major continents, Mars has very thin sheets of plagioclase over very small areas, e.g. at Syrtis Major, and Venus may have two small granitic continents (Ishtar and Aphrodite Terra). In my "Planetary Formation and Biogenesis" Earth formed through aluminosilicates being phase-separated in the accretion disk. That is why Earth also has so much water.

Mar 31, 2015
Without continental crust, the whole planet would be covered with water - No water got here afterwards.

thick silicic crust—are a unique characteristic of Earth." - No way you can know this answer.

The only thing I agree with is the earth recycles itself.

Apr 01, 2015
Most scientists are acutely aware of just how much there is yet to know. But just because the last page of the book is yet to be written doesn't mean the pages we're writing now aren't exceedingly important or groundbreaking.

The idea that continental crust is actively produced instead of merely recycled could dramatically change how we do future geology.


*** I just got here and haven't even read the article, but didn't want to lose your comment: Obviously subducted continental material is 'recycled', and there is a finite amount of material in earth which is contantly rising, falling, convectiing, etc. (lava lamp?)

Obvioiusly new land mass - usu volcanic - is 'new'. This is nothing new. What do you mean?

Apr 01, 2015
"Without continental crust, the whole planet would be covered with water," said Esteban Gazel, an assistant professor of geology with Virginia Tech's College of Science. "Most terrestrial planets in the solar system have basaltic crusts similar to Earth's oceanic crust, but the continental masses—areas of buoyant, thick silicic crust—are a unique characteristic of Earth."

The bouyancy is being affected by our mass removal of very low specific gravity gas from shale (bouy) formations in earth, and replacing it with hi sp gr liquids after fracturing the solid porous structure.

Besides that the earth (from the core) is warming some (a normal cycle) we are aggrevating it by fracking so much.

At the same time, continental ice is melting, and in some cases building elsewhere. Whether net building or melting, the weight distribution is shifting.

Coming is a worldwide tectonic shift, plates moving farther and faster than believed possible.
over, under, sideways, down - hey!

Apr 01, 2015
Three names. Has that one ticked as well.
To whit:
John Wayne Gacy
...


And now The Venerable Ricky Shawatza Hall

Apr 01, 2015
@ AGreatWhopper:

Is Scientific American crazy also? Here's a quote from one of their recently published articles titled "Fact or Fiction?: Dark Matter Killed the Dinosaurs. (March 25, 2015):

"Scientists would be forced to consider the histories of Earth and the solar system's other rocky worlds in a galactic context .... Most geologists will not like this, as it might mean that astrophysics trumps geology as the underlying driver for geological changes..."

...and if you do some research, you'll find that there is a small library of peer-reviewed research findings that are indicating that geological, climatological, and many primary biological processes are driven by exoterrestrial mechanics.

Apr 01, 2015
"new research shows "juvenile" continental crust has been produced throughout Earth's history."

Funny how everything comes together. In the last few days I've read a 2010 paper of Sleep who proposed that continental crust, if different, was present at the outset in the Hadean.

Then a web conference proceeding video from early 2015 that proposed a plausible mechanism. The constraint forcing this would be the 3 times heat flow, so 10 times faster plate tectonics, so an initial "break off and drop" start of subduction, coupled with some initial crust forced to stay on top. The same guy noted how it could reconcile the Jack Hill zircon +3.5 Gyrs data of both having early oceans (oxygen isotope ratios) and continental recycling (um, beryllium isotope ratios I think, plus the mere existence of these recycled zircons).

And now this test of the existence of juvenile continental crust.

Apr 01, 2015
@poorpeter: Yes, subduction recycles oceanic crust, and destroys some continental crust. But continental crust floats on top, and its formation and maturation has been largely unknown. But no longer. [Personally, I would nitpick that island arcs, which can be spawned by colliding oceanic plates, are known sources for continental crust, at least in models. But this paper tests maturation, and makes the overall process valid.]

Apr 01, 2015
Sigh.

@ian_miller: That is a personal theory. Do you have any peer reviewed references?

@jeffreyjoemiller: If you get your science from Scientific American, or pull it here from press releases without checking peer review et cetera, I would say that you are halfway to crazy town - as dependent on unwarranted belief as the religious.

There is a lot of speculative ideas like the insipid "dark matter" Milky Way disk paper, which rely on old and statistically erroneous papers on mass extinction that attempted to derive peridoicity in the fossil record. The most comprehensive and statistically robust paper (used autocorrelation) is Alroy from 2008, what I know of, and it is definitive. [ http://www.pnas.o...536.full ]

[tbctd]

Apr 01, 2015
[ctd]

***There simply is no periodicity in the fossil record. Mass extinctions are statistically drawn from the same distribution as smaller extinctions on all scales, which ultimately derives as species speciated and extinct from independent, environmental, contingent, conditions.***

The whole astronomical "exoterrestrial mechanics on biology" field is pure wish-thinking buffoon balloney, and somewhat good biologists should know it.

Apr 01, 2015
@ Torbjorn_Larsson_OM

re: periodicity in the fossil record...the causes of it are well documented.

Nir Shaviv, professor of physics at the University of Toronto: As the solar system passes through the galaxy's spiral arms, major extinction events occur on Earth related to asteroid bombardment. His charts plotting Earth's ice ages against passage through the arms of the Milky Way corroborate this.

And FIrestone, West, and Varwick-Smith, and Clube and Napier, calculated that, because of the subtle changes in the orbits of Earth and the remaining cosmic debris of a very large comet that entered the solar system 200k years ago, Earth crosses through the densest part of the giant comet clouds every 2,000 to 4,000 years, and starting in the year 2000, continuing for 400 years, Earth is in a dangerous time of potential collision with the densest part of these clouds containing some very large debris. So yeah, periodicity. Volumes of other data also.

Apr 01, 2015
@ Torbjorn_Larsson_OM

"astronomical "exoterrestrial mechanics on biology" field is pure wish-thinking buffoon balloney"

Institute of Space Studies - Russian Academy of Sciences / Sechenov Moscow Medical Academy: solar activity can disrupt the human heart beat. 70% of solar triggered geomagnetic storms are accompanied by abnormally high rates of heart attacks ... repeated studies show that solar storms increase human metabolic activity.

F. Feigin, Auckland University of Technology: solar activity that trigger geomagnetic storms related to increased risk for strokes. "As it is known that 2014 is a year of high geomagnetic activity, we can expect a higher stroke rate this year." (Medscape Medical News, 2014)

Persinger, Raps, Stoupel, Shimshoni, Kuleshova, Zakharov, Tyrnov, Tarquini, Perfetto, and Tarquini and many more: wide variety of studies repeatedly document strong correlations between solar triggered geomagnetic disruptions and cardiac and psychiatric events.

Apr 01, 2015
@ Torbjorn_Larsson_OM, I'm assuming by your comments that you must have a medical degree with specialization in chronobiological processes, and also doctorates / research experience in geology, astrophysics, exobiometeorology, and probably psychiatry also. Please post your peer reviewed papers that support your
"buffoon / "balloney" dismissal of fossil periodicity and the lack of interactive relationship between Earth's biota and exoterrestrial processes and cycles. I'd be interested in reading them. ;)

Apr 01, 2015
@jefferyjoe

Where are the links to the bs you're claiming?

Apr 01, 2015
Vietvet...if you have any informed interest in these subjects, then you also know how to locate the studies I referenced.

Apr 02, 2015
Previous to these findings, the best understanding has been that the _continental_ crust originally formed via bulk density differences in the slowly cooling melt of the earth's formation, and since, only small amounts of andesitic/granitic/rhyolitic "continental" were recycled via subduction of seafloor plates under continental plates by the increased heating in these zones caused by the introduction of water into the underlying mantle. causing some limited chemical transformation of basaltic(seafloor) crust into A/G/R(continental) crust.
However, this research is showing that quite large amounts of A/G/R crust is formed as a result of subduction along the boundary of _two seafloor plates_ which adds a significant amount of additional A/G/R crust(over geologic time), to the original continental crust formed via the adiabatic cooling of the primordial melt, which has -until now- been thought to be more-or-less all the continental crust there would ever be.

Apr 02, 2015
Vietvet...if you have any informed interest in these subjects, then you also know how to locate the studies I referenced.
@jeffreyjoemiller
quit being so defensive
there have been a lot of bs claims here on PO and there are a large number of people trying to get others to link references
not just cite them in a post
(usually because of the additional work involved in tracking down the EXACT reference as well as getting hold of the entire reference, which is sometimes paywalled)

Producing the links will alleviate the unnecessary back and forth between a mis-read study and the posters intent
Like saying Lacis et al ... Lacis has published quite a few studies with others
to clarify, one simply links specific references

i, for one, would like to read the linked references

Also- articles are not studies, so don't bother linking those UNLESS they have referenced studies that can be access with them
THANKS

Z99
Apr 06, 2015
Earth's primadorial water was (very probably) lost during formation and early bombardment; hence the question of "Where does Earth's water come from?" is an active research area. Plate tectonics implies some mixing during the cycle. As the Earth cools, plate tec. will slow and finally cease. This will certainly occur before compositional differentiation is complete (since the latter process isn't complete in any finite time period). IOW, the question isn't whether any "new" crust is forming, but what is the magnitude of that relative to the amount of recycling.

Apr 08, 2015
Oops! I didn't check this thread timely.

@jeffreyjoemiller:

"re: periodicity in the fossil record...the causes of it are well documented."

I didn't discuss causes, but pointed out there simple isn't the periodicity you claim.

"Please post your peer reviewed papers that support your "buffoon / "balloney" dismissal of fossil periodicity".

I did!

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