The Origins Of Fossil Fuels [NU013]
Ben Franklin Centre for Theoretical Research
PO Box 27, Subiaco, WA 6008, Australia.
"Science when well digested is nothing but good sense and reason"
By now we have set the scene for a more detailed look at the origin of fossil fuels. Of
course, the main fossil fuels are coal, mineral oil, and natural gas, with a few less important
sources such as lignite, bitumen, and tar sands.
The outstanding feature of all fossil fuels is that they contain a lot of carbon. Coal is
especially rich, with up to 95%. The others are mainly hydrocarbons, compounds of carbon
with hydrogen, sometimes with other elements present, but even in these the proportion of
carbon is high, around 82-87% by weight.
Coal was one of the earliest minerals to be be developed in today's technological society,
in fact it was one of the main props for the Industrial Revolution, which started in Britain.
Britain has considerable coal deposits and a long history of geological discovery, so the nature
of coal deposits in that country have become known in great detail.
Figure 13.1 (taken from the 1875 Encyclopaedia Britannica) shows the various geological
strata found in conjunction with the Coal Measures of different parts of Britain. The actual
coal seams vary in thickness from a mere film to as much as 15 metres. In other parts of the
world even thicker seams have been found, as in the south of France and in India, up to 60 m thick or more.
Fig. 13.1. Carboniferous strata in Britain
Of course even the rich coal deposits form only a small fraction of the total rock strata,
which in the Carboniferous of Britain can be more than 4 km thick. The majority of the rock
is made up of typical sedimentary strata, in particular sandstones, limestones, and shales.
Although the majority of important coal deposits of the world are of Carboniferous age,
some are found in the Permian period which follows, and also in the younger rocks of the
Mesozoic and Cenozoic. The younger deposits are usually much less compacted ('brown
coal'), have more moisture, and have clearly undergone less conversion from the original plant
Older, more compact coals have little moisture and are richest in carbon, having as much
as 95%, the rest being hydrogen, water, and ash. In good coals of any age the ash content is
quite low, below 2%. This is similar to the ash content of the above-ground portions of modern
How did coal originate? The answer to this is to be found in any geology textbook, which
describes the vast swamps of the Carboniferous Period, with their giant primitive trees and
strange animals. That some such plant provenances existed is undoubted -- there are too many
well-preserved fossil plants involved in the Coal Measure deposits of the Earth to be able to
reject the notion. But the standard swamp picture has a number of serious deficiencies.
Puzzles of Coal Formation
All the sedimentary strata enclosing coal are typical of offshore deposits, deposits laid
down in the seas. Limestones are almost invariably of marine origin, sandstones are normally
produced on the sea floor from particles washed in by rivers or off the coasts. Shales may be
formed from the mud of lakes, but are more typical of offshore seabed areas, beyond the point where the coarser sand particles have already
Why should coal seams be enclosed in
these typically marine deposits? Why is coal
relatively pure carbon, without much trace of
any soil remains? Why are 'marine bands',
deposits obviously derived from the sea
, often found within the coal
seams? Why are fossil mussel shells often
associated with coal? Why are deposits of
coal sometimes associated with salt beds?
These questions are even more perplexing
when you take into account the relatively
small amount of land surface which existed
during the Carboniferous, if the approach
used in this book is to be believed. Modern
high-carbon deposits are being formed on
land today, within our swamps and marshes
(initially as peat), but their thickness is not
great, especially after conversion and compression
to a composition and density similar
to that of coal.
An answer to some of these difficulties
may be found in the following suggestion.
Could it have been the case that these vast
Coal Measure swamps existed, not on land,
but on the surface of the sea? Was coal, and probably much of our oil and gas deposits, formed from material sinking to the floor of shallow
seas, at a time when all seas were relatively shallow (because expansion had not then
proceeded to the stage where ocean deeps existed)?
Most coal deposits were produced by the conversion of plants
which had grown up floating on the surface of the sea
"Impossible!" would be the first response. How could the tall Coal Measure plants, clearly
adjusted to fresh water, exist on the sea?
The Quaking Forests
A fascinating and unusual landscape feature can sometimes be encountered which is
known as a Quaking Forest. You walk through the pine forests, and suddenly you notice that
the trees are swaying, although there is no wind. They only sway where you are walking. The
march of the Ents, perhaps, from Tolkien?
The explanation for a Quaking Forest is simple. It is a forest which has grown on top of
a lake, on a layer of floating plant debris which has gradually accumulated and grown out from
the original lake edge. This phenomenon is well known and accepted with some mangrove
swamps, growing out from river banks, sometimes completely choking a river. But with a
Quaking Forest, there is actually a pocket or lens of water left between the underside of the
mass of plant roots and the solid mud which formed the bed of the lake.
It is like a layer of moss growing on the top of a waterbed -- push your finger down into
the top and the closer stems bend towards you. As you release your finger, or as waves travel
out from where you pushed down, the stems bend and sway, back and forth.
It might be argued that the huge Carboniferous plants were too big to float on the surface
of the sea, they would fall over. But, of course, the pines do it now in a Quaking Forest. And,
in the densest, tallest, and most prolific rainforests of today, the root systems of the huge trees
are surprisingly shallow. They resist falling over partly by developing buttresses, but more
importantly through the shelter of their environment protecting them from winds. We have
already seen, in NU011, how the Carboniferous conditions were probably of dense, still
air under an impenetrable cloud cover which would suppress air movements.
The Floating Swamps
The picture we are building up is perhaps not too different to the accepted swamp scenario,
but with one vital difference -- the swamps were not on land, but on the sea. This would
explain much. It would explain why the coal seams are interleaved with marine sedimentary
rocks, marine shell bands, and occasionally salt beds. It would explain the comparatively wide
extent of coal deposits in the land-poor Carboniferous world. It would explain the low ash
content of coals, if the plants they were derived from grew in the absence of soils.
How about the saltiness of the sea? We have already seen (Propositions 10I, 10J) that the
salinity is likely to have increased continously up to the present time, so the seas would have
been less salty during the Carboniferous than they are now. Moreover, it would be possible
for a thick continuous mass of floating organic material to be saturated with fresh water, even
though it was floating on salty water.
Fresh water is less dense than salt water, and under calm conditions it could easily happen
that the floating plant layer, soaked in the rain which we have seen was probably falling
continually, was stabilized enough so its fresh water did not mix with underlying more salty
layers on which it floated. After all, that is not so very different from present conditions where
a plant is growing in a soil, wet with fresh water, which overlies a deeper water table where
the water is known to be salty.
If the scenario I have painted for the early days of life on Earth is correct, we are looking then at a much smaller Earth, with less land than now, but also much less extensive seas.
Instead of the rolling oceans of today, the seas would mostly be relatively shallow interdomain
gulfs, perhaps none more than 100 km across, and there would be no deep oceans.
Of course there could still be the conventional shore-line swamps, but these would be only
a minor component, blending in continuously with the on-sea swamps. The latter would build
up a thicker and thicker layer of plant material, the bottom part of which would break off
periodically and sink down to the bottom of the sea. Or possibly whole floating islands could
break off, like icebergs calving from a glacier, and later sink further out to sea. In these ways,
in quiet times, very thick seams of what was to become coal could be accumulated.
When times were not so quiet, and domains were in active movement, the floating swamps
might be washed or blown away. Newly-upraised land would erode and provide abundant
sedimentary material to cover the coal. As the interdomain gulfs widened with Earth
expansion, these sedimentary layers would be covered with the fine muds of more offshore
areas, and perhaps the limestones of the still, warm seas.
Coal deposits were laid down in the narrow and shallow
interdomain gulfs produced by early Earth expansion
The Petroleum Story
While coal was the energy mainstay in the early development of modern industry,
petroleum is a latecomer in this respect, a child of the 20th Century. During this century it has
moved from an energy source of little consequence to be the principal source of our needs. In
the present context, petroleum can be taken to include both oil-type sources which are liquid
under normal temperatures and pressures, and natural gas.
Both types frequently occur together, often with the gas dissolved in the oil, often under
very high pressure -- helping to make a self-pumping 'gusher'. Natural gas as a developed
energy source is even newer than oil, dating back only to the 1950s. Before this, the gas was
usually regarded as an annoying byproduct which was burnt off or otherwise went to waste.
Of course there are instances of practical use of petroleum, dating far back into the past.
Natural seepages of oil (asphalt and bitumen) were used in the Middle East by the Sumerians,
Assyrians, and Babylonians some 5000 years ago, in building mortar, road construction, and
Petroleum is very commonly associated with salt, and as the use of deep drilled wells was
once primarily for the extraction of brine (concentrated natural salt solutions), it has often
figured as an unwanted discovery. This was the case with the early Chinese, who around
200 BC drilled a 140 m deep well to extract brine and were annoyed to get gas as well.
Subsequently they worked out how to burn the gas and use it to evaporate the brine in making
Even the early work in the United States, where large-scale petroleum extraction was
pioneered, had a similar history. In 1819 a well being bored for brine in Kentucky yielded so
much black petroleum that it was abandoned in disgust. In 1829 another Kentucky brine well yielded a huge flow of several thousand tonnes of oil, most of which was wasted, although a
little was bottled and sold for liniment (as 'American oil'). It was not until 1859 that a well
was bored specifically to extract petroleum, in Pennsylvania.
Formation of Petroleum
There are obvious similarities and links between petroleum and coal, and a number of
obvious differences. Chemically, petroleum sources are principally hydrocarbons, compounds
of carbon and hydrogen, whereas in coals much of the corresponding hydrogen has
been eliminated. Both fossil fuel sources are essentially complex mixtures, with no two
deposits chemically identical. Coal often has a much higher sulphur content than petroleum,
and for this reason has lost favour for domestic use with increasing concern over air pollution.
Physically, petroleum sources are fluids whereas coal is a solid, and this has important
consequences. As a fluid, petroleum can migrate, and the rocks from which it is extracted are
often not the same as the ones in which it was formed. It also means that to be available for
large-scale extraction, the petroleum must be 'trapped' in the rocks in some way, as with
impermeable layers of clay, shale, or salt around it.
The reservoir rocks which hold the petroleum are mostly sandstones (59%) and limestones,
including dolomites (40%), the same typical sedimentary rocks which were associated
with coal. Less than 1% of the world's oil has been found in fractured igneous or metamorphic
rocks, which typically lack the pore or void space needed to be successful reservoir rocks.
There seems no doubt that, whatever their mode of formation, both coal and petroleum are
essentially derived from the remains of living creatures. In Proposition 13A, I made the
possibly novel suggestion that coal was formed from the remains of plants growing floating
on the seas. It seems very likely that petroleum had a similar origin.
Oil and gas deposits were formed from the remains of plants
which had grown floating on the surface of the sea
Amusingly enough, while the coal proposition in 13A may lead to outraged protests, the
almost identical one for oil will not -- it is close to the currently accepted view. This is that
the major source of petroleum was floating plankton, minute marine plant and animal
organisms, which grew in shallow seas.
Fuller details of the reasons for concluding that petroleum has an organic origin, and that
its major source was marine plankton, are given in the 1974 Encyclopaedia Britannica article on
Petroleum . The paragraph on the origin of petroleum concludes "In
spite of the great amount of scientific research ... there remain many unresolved questions
regarding its origin".
It does seem possible that, even though Proposition 13C can be regarded as the accepted
view, the floating plankton source idea may need modification in two ways. The first is to
suggest that what are regarded as 'land' plants formed an important, or even the principal,
source of the petroleum material. In other words, these plants grew on floating mats on the sea, just as suggested for the coal deposits. And the remains of plants which are accepted as
being of 'land' types are not uncommon in some petroleum deposits.
The second point has more implications; this is the suggestion that the floating mats of
material were essentially continuous, forming closed capping layers over the surface of the
sea. While these layers may not have been as thick and 'trafficable' as the coal ones, able to
support quite tall trees, they still may have been able to effectively seal off the underlying sea
from the atmosphere and from normal evaporative processes.
The floating layers of plants which provided the source
material for petroleum and coal were able to seal off significant
areas of the seas and prevent normal evaporation
If this Proposition is found to be valid, it has considerable implications for the formation
of both fossil fuels and for salt. It is not disputed that the formation of fossil fuels from organic
materials needs anaerobic conditions, those where oxygen is lacking. This is because the
actual conversion is done by anaerobic bacteria which can only function where there is no
oxygen -- these are the organisms responsible for production of marsh gas (methane) from
bogs, which lack oxygen under their surfaces.
Clearly sealing off the surface of a shallow sea with organic material would allow its water
to become completely anaerobic and enable the conversion of plant remains under the surface
to coal and petroleum.
Seas sealed from the atmosphere with a floating organic layer
would become anaerobic and foster the conversion of organic
material to fossil fuels
It has always been assumed that rock salt deposits, which are sometimes of great thickness,
were formed by conventional evaporation of water from the surface of enclosed lakes or seas.
This may well be the case, but it is also possible that they were formed from sealed seas.
If domain movement caused the uplift of a sealed-sea area, or some other change occurred
to reduce the rain falling on such an area, it would be expected that the water in the sea would
be gradually diminished and would disappear. Even if the floating plant layer was completely
dead, water would continuously rise through the sponge-like layer and be evaporated, leaving
the salt behind. Once a certain salt concentration was reached, the special properties of such
salt solutions for holding thermal inversion layers could accelerate this process, leading to the
formation of thick salt layers beneath the organic seal.
Some salt deposits were formed by the elimination of water
from sealed-sea areas
Of course this suggestion does match in with the observed association of salt with coal and
The Age of Fossil Fuels
We have seen that most black coal deposits were formed in the Carboniferous, with some
in the Permian, in the last two periods of the Paleozoic. Most petroleum deposits are found
in the rocks of the Mesozoic (63%) and Cenozoic (29%), with only 8% in Paleozoic rocks, and
almost none in the Precambrian.
Of course petroleum is known to migrate from its strata of accumulation, but these figures
do fit in well with Expanding Earth scenarios and other suggestions already made. Coal
deposits are mostly in current land areas, whereas oil and gas fields are increasingly being
developed on offshore areas, on the continental shelves. In the modern deep ocean beds, which
are comparatively young, under 200 my old, no fossil fuel deposits at all are found.
The inference is that the fossil fuel deposits were laid down at the bottoms of the deepest
seas which then existed.
Fossil fuel deposits were formed at the bottoms of the deepest
seas which then existed, from plant sources floating on those seas
The scenario is this. In Paleozoic times, the only seas which existed were fairly shallow
and lying in the new interdomain gulfs, and it was in these that the coal plants were dumped.
With increasing Earth Expansion, these areas are now mostly above sealevel. As expansion
continued into the Mesozoic, new and lower interdomain gulfs opened up. It was into these
that most of the petroleum plants were deposited, and it is these areas which are today mostly
lower and at continental-shelf level.
Advancement into the Cenozoic saw the development of the modern deep ocean basins,
and with this, changes in conditions to largely eliminate fossil fuel formation. The great
floating plant mats died off, unable to survive in the blustery open ocean conditions, increasing
salinity, and reduced carbon-dioxide content of the air. Their disappearance meant that the
anaerobic conditions needed for plant conversion could no longer be attained in the ever-deepening
The Matter of Sulphur
A minor point mentioned above was that coal deposits often have high sulphur contents,
which makes them less suitable than oil or gas for domestic use, because the sulphur can lead
to air pollution.
Evidence which we have seen so far gives us an explanation for this difference. It seems
likely that there was much more sulphur in the air in Paleozoic times, and this too, like the
ammonia and methane, was largely eliminated by the start of the Mesozoic.
The Paleozoic atmosphere originally contained much more
sulphur compounds, which were largely eliminated by the start
of the Mesozoic
In the primeval atmosphere, sulphur was likely to have been present as hydrogen sulphide,
the gas which gives the smell to rotten eggs. This is likely to have been converted to sulphur
dioxide, the most common oxide of sulphur, by the start of the Paleozoic (when free oxygen
Both hydrogen sulphide (molecular weight 34) and sulphur dioxide (mw=64) are relatively
heavy gases (see Table 11). Because of this, they are not likely to have been appreciably lost
into space, but instead incorporated into sulphate sedimentary rocks when the right chemical
* * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
(Full list of references at NURefs)
. Encyclopedia Britannica. 1974 edition.
. F H T Rhodes. A evolucao da vida. Ulisseia, Lisboa, 1960.
NU014: Geoprospecting and Mineral Riches
NU012: Death Of The Dinosaurs
Go to the NUSite Home Page
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