fossils are chemicals found in rocks that provide an
organic signature for ancient life. Molecular fossils
and isotope ratios represent two types of chemical
fossils are often referred to as biomarkers or
biosignatures and represent products of cellular biosynthesis
that are incorporated into sediments and eventually into
of these chemicals become altered in known ways and can
be stable for billions
acids (DNA & RNA), proteins, and carbohydrates
do not survive long in the geologic environment. The
of biomarkers are hydrocarbons derived from membrane
lipids, which under certain conditions can be stable
years. Molecules derived from pigments, such as chlorophyll,
can also act as biomarkers. In 1936 Alfred Teibs recognized
that vanadyl porphyrin was
helped support a biologic origin for petroleum (Knoll,
summons, Waldbauer, & Zumberge, pp. 134-135).
fuels petroleum (crude oil), coal, and natural gas are
the result of biologic activity and contain chemical
fossils. Major coal deposits represent plant
grew primarily during the Carboniferous period.
Crude oil and natural gas formed primarily from prehistoric
algae and zooplankton that were deposited on the ocean
floor under anoxic conditions. Natural gas can
also form from fossil plant material. During sedimentary
rock formation the remains of algae and zooplankton are
converted into a mixture of organic hydrocarbons known
as kerogen. Over geologic time heat and pressure can
convert kerogen into oil or natural gas. The majority
of oil deposits are Mesozoic or Cenozoic in age.
is interesting to contemplate the origins of fossil
fuel energy. Ancient plants and algae converted
solar energy into the chemical
bond energy of carbohydrates. Converted energy
from the Sun was then passed through
the food chains
Organic chemicals from these organisms were incorporated
into sediments and eventually rock. So, the fossil
fuels we humans have come to depend upon represent
ancient sunshine stored within the Earth's crust.
fuels currently provide more than 85% of all the
energy consumed in the United States. Crude
oil supplies 40% of our energy
fuel for cars and trucks. Coal is the major
source of energy for generating electricity worldwide (U.S.
Department of Energy). We depend upon fossil fuel
our agriculture. Some studies estimate that without
fossil fuels the United States could only sustain
two thirds of its current population (Pfeiffer,
D.A., 2006, p. 41). Our dependence upon these nonrenewable
resources should be a wake up call to invest in
and develop alternative energy sources. At present,
it is clear that coal, oil and natural gas, chemical
fossils in the form
of fossil fuels, are the lifeblood
of America's economy.
paleontologists and geobiologists the information
provided by molecular fossils varies greatly.
Some molecular fossils can help to determine what organisms
were present, while others can indicate what biosynthetic
pathways were in operation, still others provide information
regarding the depositional environment (Knoll,
Summons, Waldbauer, and Zumberge, 2007, p. 135).
ratios represent another type of chemical fossil and
result from metabolic processes that preferentially
one form of an isotope over another (Cowen, R. p. 16).
Molecular fossils represent biomolecules or their derivatives
that were once part of a living organism. In this
way, molecular fossils are similar in concept to
conventional body fossils. Isotope ratios are not
of an organism,
they result from activities during life and
in this way
are analogous to trace fossils.
first chemical evidence of photosynthesis, in the
to C-13 ratios, can be found in Archean rock of 3.8
from Isua, Greenland (Kenrick & Davis, 2004, pp
10-11; Johnson & Stucky, 1995, p 22). The process
of photosynthesis preferentially utilizes C-12 over
C-13 when removing
CO2 from the air to synthesize carbohydrates, creating
of these carbon isotopes that differ from normal background
ratios. Thus, carbon compounds processed by photosynthetic
organisms are enriched with C-12 (Rich & Fenton,
1996, p 91). The enrichment of C-12 in rocks is a test
presence of life. Carbon isotope ratios consistent
with presence of cyanobacteria are widespread in rock
at 3.5 Ga (Johnson & Stucky, 1995, p. 22). One
problem with the evidence above is the fact that chemical
in non-photosynthetic autotrophs and nonautotrophs
can produce C-12 enrichment (Blankenship, Sadekar, & Raymond,
2007, pp 22-23).
of Primary Producers in the Sea
fossils have been a key to understanding the evolution
of primary producers in Earth's oceans. Microfossils and
molecular fossils have helped to establish that Earth's
oceans have experienced two major shifts in the composition
of primary producers. Initially, cyanobacteria along with
other photosynthetic bacteria were the primary producers
during the Proterozoic eon. The first shift occurred during
the early Paleozoic era when eukaryotic green algae joined
cyanobacteria in being major primary producers. The second
shift would occur during the Mesozoic era when dinoflagellates
and coccolithofores would be joined by diatoms in the Jurassic.
Diatoms, dinoflagellates, and coccolithophores would assume
their dominant role as the base of many modern marine ecosystems
by Cretaceous times. (Knoll, Summons, Waldbauer, and Zumberge,
2007, p. 155).
Sadekar, & Raymond.
(2007). The Evolutionary Transition from Anoxygenic
to Oxygenic Photosynthesis. In Falkowski, P.G. Knoll,
A.H. [Eds] Evolution of Primary Producers in the
Sea. (pp. 21-35). China: Elsevier Academic Press.
Cownen, R. (2005). History of Life [4th Edition]. Malden, Main: Blackwell
K.R. & Stucky R.K. (1995). Prehistoric Journey:
A History of Life on Earth. Boulder, Colorado: Roberts
P. & Davis, P. (2004). Fossil Plants. Washington:
Summons, Waldbauer, and Zumberge. (2007). The Geological
Succession of Primary Producers in the Oceans. In Falkowski,
P.G. Knoll, A.H. [Eds] Evolution of Primary Producers
in the Sea. (pp. 133-163). China: Elsevier Academic
D.A. (2006), Eating Fossil Fuels: Oil, Food and the
Coming Crises in Agriculture. Canada: New Society Publishers.
P.V., Rich T. H., Fenton, M.A., & Fenton, C.L. (1996).
The Fossil Book: A Record of Prehistoric Life.
Mineola, NY: Dover Publications, Inc.
Department of Energy: http://www.energy.gov/energysources/fossilfuels.htm