From: Roger Olson (rogero@saintjoe.edu)
Date: Thu Nov 13 2003 - 15:21:15 EST
Steven, Glenn, et. al..,
"...A staggering 98 tons of prehistoric, buried plant material -- that's
196,000 pounds -- is required to produce each gallon of gasoline... "
A quick technical question --- doesn't most petroleum originate from the
burial and thermal maturation of marine protists (zoo- and
phytoplankton) rather than "plant material"? Or is this article simply
giving a plant analogy of the sheer volume of equlivalent organic
material needed to produce a gallon of petrol?
Thanks for clearing this up. I'm not a geologist, but take some
interest in the subject.
Roger
Steven M Smith wrote:
>After skimming several posts on this ASA thread I ran across the following
>web article from SpaceDaily.com which addresses several of the issues under
>discussion. I'll just include a few 'teasers' here. You can read this
>popular account of the study at
><http://www.spacedaily.com/news/energy-tech-03zp.html>
>
><<Ninety Eight Tons Of Primordial Plant Matter Per Gallon
>Salt Lake City - Oct 27, 2003
>
>A staggering 98 tons of prehistoric, buried plant material -- that's
>196,000 pounds -- is required to produce each gallon of gasoline we burn in
>our cars, SUVs, trucks and other vehicles, according to a study conducted
>at the University of Utah.>>
>
>[Snip]
>
><<Dukes also calculated that the amount of fossil fuel burned in a single
>year -- 1997 was used in the study -- totals 97 million billion pounds of
>carbon, which is equivalent to more than 400 times "all the plant matter
>that grows in the world in a year," including vast amounts of microscopic
>plant life in the oceans.>>
>
>[Snip]
>
><<To determine how much ancient plant matter it took to eventually produce
>modern fossil fuels, Dukes calculated how much of the carbon in the
>original vegetation was lost during each stage of the multiple-step
>processes that create oil, gas and coal.
> He looked at the proportion of fossil fuel reserves derived from
>different ancient environments: coal that formed when ancient plants rotted
>in peat swamps; oil from tiny floating plants called phytoplankton that
>were deposited on ancient seafloors, river deltas and lakebeds; and natural
>gas from those and other prehistoric environments. Then he examined the
>efficiency at which prehistoric plants were converted by heat, pressure and
>time into peat or other carbon-rich sediments.
> Next, Dukes analyzed the efficiency with which carbon-rich sediments
>were converted to coal, oil and natural gas. Then he studied the efficiency
>of extracting such deposits. During each of the above steps, he based his
>calculations on previously published studies.
> The calculations showed that roughly one-eleventh of the carbon in the
>plants deposited in peat bogs ends up as coal, and that only one-10,750th
>of the carbon in plants deposited on ancient seafloors, deltas and lakebeds
>ends up as oil and natural gas.
> Dukes then used these "recovery factors" to estimate how much ancient
>plant matter was needed to produce a given amount of fossil fuel. Dukes
>considers his calculations good estimates based on available data, but says
>that because fossil fuels were formed under a wide range of environmental
>conditions, each estimate is subject to a wide range of uncertainty.>>
>
>[Snip]
>
><<Unlike the inefficiency of converting ancient plants to oil, natural gas
>and coal, modern plant "biomass" can provide energy more efficiently,
>either by burning it or converting into fuels like ethanol. So Dukes
>analyzed how much modern plant matter it would take to replace society's
>current consumption of fossil fuels.
> He began with a United Nations estimate that the total energy content
>of all coal, oil and natural gas used worldwide in 1997 equaled 315,271
>million billion joules (a unit of energy). He divided that by the typical
>value of heat produced when wood is burned: 20,000 joules per gram of dry
>wood. The result is that fossil fuel consumption in 1997 equaled the energy
>in 15.8 trillion kilograms of wood. Dukes multiplied that by 45 percent --
>the proportion of carbon in plant material -- to calculate that fossil fuel
>consumption in 1997 equaled the energy in 7.1 trillion
>kilograms of carbon in plant matter.
> Studies have estimated that all land plants today contain 56.4
>trillion kilograms of carbon, but only 56 percent of that is above ground
>and could be harvested. So excluding roots, land plants thus contain 56
>percent times 56.4, or 31.6 trillion kilograms of carbon.
> Dukes then divided the 1997 fossil fuel use equivalent of 7.1 trillion
>kilograms of carbon in plant matter by 31.6 trillion kilograms now
>available in plants. He found we would need to harvest 22 percent of all
>land plants just to equal the fossil fuel energy used in 1997....>>
>
>Nothing was said in the SpaceDaily.com article about the energy costs
>needed to grow and harvest 22% of all land plants. The article concludes:
>
><<"Relying totally on biomass for our power -- using crop residues and
>quick-growing forests as fuel sources -- would force us to dedicate a huge
>part of the landscape to growing these fuels," Dukes says. "It would have
>major environmental consequences. We would have to choose between our rain
>forests and our vehicles and appliances. Biomass burning can be part of the
>solution if we use agricultural wastes, but other technologies have to be a
>major part of the solution as well -- things like wind and solar power.">>
>
>_____________
> Steven M. Smith, Geologist, U.S. Geological Survey
> Box 25046, M.S. 973, DFC, Denver, CO 80225
> Office: (303)236-1192, Fax: (303)236-3200
> Email: smsmith@usgs.gov
> -USGS Nat'l Geochem. Database NURE HSSR Web Site-
> http://pubs.usgs.gov/of/1997/ofr-97-0492/
>
>
>
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