[meteorite-list] Mass Extinction from Buried Carbon?

From: Steve Schoner <steve_schoner_at_meteoritecentral.com>
Date: Thu Apr 22 10:21:08 2004
Message-ID: <20030725185438.66481.qmail_at_web12702.mail.yahoo.com>

Carbonate volcanoes?

I think that there is at least one such volcano in
Kenya.

It exudes a soda, carbonate lava at temperatures at
about 1000 degrees.

The primary gas from this amazing lava is carbon
dioxide.

Now the question,

If carbonates melt at much lower temps than olivine,
could it be that the carbonate veins found in NWA998
were the products of such intrusions on Mars, and then
weathered later?

Steve Schoner/ams


--- Ron Baalke <baalke_at_zagami.jpl.nasa.gov> wrote:
>
>
>
http://dsc.discovery.com/news/afp/20030721/carbon.html
>
> Mass Extinction from Buried Carbon?
> AFP/ABC Science Online
> July 23, 2003
>
> A vast reservoir of carbon is stashed beneath the
> Earth's crust
> and could be released by a major volcanic eruption,
> unleashing a
> mass extinction of the kind that last occurred 200
> million years
> ago, German geologists report.
>
> Researchers know that carbon is stored in the
> mantle, a layer of
> plastic-like rock beneath Earth's fragile crust,
> said Hans
> Keppler of the Institute of Sciences at Germany's
> University of
> Tuebingen, whose report appears in today's issue of
> Nature.
>
> Exactly how much is down there is unknown. Most
> estimates, drawn
> from analyses of gases emerging from the mantle,
> suggest the store
> is many times more than all the carbon in the
> Earth's atmosphere,
> soil and sea combined.
>
> The concern is that if just a part of this gigantic
> reservoir is quickly released as carbon dioxide, or
> CO2, that could create a runaway greenhouse effect.
> The CO2-soaked atmosphere would store up heat
> from the sun, shrivelling plant life and destroying
> species along the food chain.
>
> "The [mantle] reservoir is just gigantic compared
> with
> anything that we have on the Earth's surface," said
> Keppler.
>
> So he and his colleagues conducted an ambitious
> experiment
> aimed at finding whether mantle rock is a stable
> storage for
> CO2.
>
> Most of the rock in the Earth's upper mantle is a
> crystalline
> silicate called olivine. In a lab chamber, Keppler's
> team
> replicated the fiery heat and intense pressures, of
> 1,200°
> Celsius and 3.5 gigapascals, which are likely to
> exist in the
> deeper parts of the upper mantle.
>
> They used these conditions to create olivine
> crystals from raw
> ingredients of magnesium oxide and silicon dioxide,
> and exposed
> them to carbon and water.
>
> The carbon turned out to be almost completely
> insoluble in olivine:
> just a tiny amount, between 0.1 and 1.0 parts per
> million by weight,
> was absorbed into the rock. So if the carbon is not
> in the olivine,
> that leaves only one major source, Keppler said: "If
> you cannot
> store the carbon in the olivine, then the only
> plausible place for
> storing it are carbonates."
>
> Carbonate rocks have a much lower melting point than
> olivine, which
> is able to absorb the punishing furnace-like heat
> radiating from the
> Earth's core and still not melt.
>
> Heated to a molten state, carbonates are capable of
> squeezing through
> cracks in the olivine, rising up towards the surface
> and absorbing the
> free carbon as they go. They can pick up so much
> that as much as 10 or
> 20 percent of their mass is carbon.
>
> The risk, said Keppler, is that this carbonate
> reservoir could suddenly
> be breached in the event of a major volcanic
> eruption.
>
> "Once the carbonate comes up to the surface, as soon
> as it is below
> [a pressure of] 20 or 30 kilobars, which corresponds
> to a depth of 40 or
> 60 kilometers in the mantle," he said. "As soon as
> it comes up beyond
> this depth, it will decompose and release carbon
> dioxide."
>
> The nightmare scenario? Gigantic geysers of carbon
> dioxide, imperilling
> life on the surface.
>
> "There has been some evidence that something like
> this has happened in
> the past. There is a very good correlation with
> [CO2] flooding that
> coincides with several mass extinction events - some
> massive, sudden
> change of carbon dioxide in the atmosphere," Keppler
> said.
>
> One of these events occurred around 245 million
> years ago, at the end of
> the Permian era, which saw the largest extinction
> event in Earth's history:
> fossil evidence shows as many as 96 percent of all
> marine species were lost
> and more than three quarters of vertebrate, or
> backboned, species on land.
>
> The other, possibly a cluster of smaller events, was
> at the end of the
> Triassic period around 208 million years ago, when
> around half of the
> world's species suddenly died out.
>
> That event essentially handed rule of the planet to
> the dinosaurs, which
> began a long decline thereafter. They were
> ultimately consigned to history
> 65 million years ago by the cataclysmic impact of a
> 10-kilometer asteroid,
> which struck what is now the Gulf of Mexico.
>
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Received on Fri 25 Jul 2003 02:54:38 PM PDT