Hello quki,
This is an interesting question for me, because geology holds a
special place in my heart. That's another story though. However,
because of that fact, I knew whom to contact. I spoke with Craig
Welsh, a graduate student in geology, and a teaching assistant and
research student in the Geology Department at the University of
Northern Iowa previously, and now at Northern Illinois University.
When I posed your question to him, he had a bit of a different answer
than you seemed to be looking for. However, as I explored more, I
found there was a # of theories on this topic.
This is what he had to say...
"Most ideas about this question say that an organism was most likely
NOT responsible. Mostly because the Pre-Cambrian predated widespread
life forms. With a few exceptions, the start of the Cambrian Period
marked the beginnings of life on Earth. Classically speaking, Pre
Cambrian means pre-life. The Earth had a drastically different
atmosphere back then that allowed iron to exist on the planet's
surface as easily and widespread as quartz sand does today. Some
geologists have theorized that large areas of the planet had huge
"deserts" of iron (think of the Sahara as not having the whitish
quartz sand but black iron sand). This "iron sand" did not oxidize
(rust) because there was almost no oxygen in the atmosphere. There
would have been wind, however, and this wind would have blown the iron
sand around in flowing dunes and such. In time, the "iron deserts"
were buried and petrified - and oxidized (Once the atmosphere allowed
it) to give that characteristic red color. When we look at petrified
dunes composed of quartz sand (like the Moab Tongue of the Navajo
Sandstone in Arches National Park), we see different colorations
outlining the bedding of the sand during its deposition. It is
theorized that the banding in iron formations is similarly related."
http://www.ucmp.berkeley.edu/precambrian/precambrian.html
Also states that there was no life on earth until the very end of the
Precambrian period, and that the atmosphere became enriched in oxygen
towards the end as well. Therefore, that's one idea backed up :)
This article states that where the deposits came from are enigmatic.
(Which is what I?ve been saying all along) :)
"Large, high-grade hematite iron ore bodies hosted by Precambrian
banded iron formations are the world's most important source of iron
ore. Despite their great economic importance, the origin of these
deposits has remained rather enigmatic."
http://www.ingenta.com/isis/searching/ExpandTOC/ingenta?issue=pubinfobike://maney/aes/2003/00000112/00000001&index=3
This article suggests that Algeal bacteria may have helped the
oxidation process along to help form the bands.
"The mineralogy of sedimentary iron ores from the Gunma iron mine are
described to evaluate the role of microorganisms and plants in ore
formation. The iron ore is composed of nanocrystalline goethite,
well-crystallized jarosite and very small amounts of strengite. The
ore characteristically occurs as thick-bands of alternating goethite
and jarosite bands, thin-bands of different goethite grain sizes, and
fossil-aggregate ore rich in moss and/or leaves. Algal fossils are
clearly preserved in the goethite bands in the thick-banded ore."
http://www.minsocam.org/MSA/AmMin/TOC/Abstracts/1999_Abstracts/JF99_Abstracts/Akai_p171_99.pdf
In addition, this article suggests that photosynthesis of
cyanobacteria, and/or microbes contributed.
"Banded Iron-Formation (BIF) constitutes the majority of the world's
iron deposits. Most commonly these deposits consist of alternating
layers of black hematite and chert. In our specimens the chert is
colored red with iron oxide impurity coated granules. BIF deposits are
a direct result of oxygen release by Precambrian microbes. During much
of the Precambrian the Earth's surface waters and atmosphere were
anoxic (oxygen-free) so that iron would exist mostly in its reduced
(ferrous or Fe2+) form. Vast quantities of ferrous iron entered the
ocean surface through volcanic action, upwelling, and run-off.
Photosynthesis by cyanobacteria in the surface waters produced oxygen
which reacted with ferrous iron to give the much less soluble ferric
iron (Fe3+), precipitating out iron hydroxide (rust). Seasonal and/or
biological cycles resulted in intervening periods when iron or oxygen
were not as available resulting in the interlayered chert
(microcrystalline quartz precipitate)."
Therefore, I can tell you it was oxygen that made the red stripes,
however, there is no conclusive evidence that I can find that it was
caused by a life form. At best, it was microbes in the first stages of
life such as these...
"Stromatolites are the dominant fossil type for most of the
Precambrian, with the oldest identified examples going back at least
3450 million years. During the Precambrian stromatolites formed reefs
comparable in extent and magnitude to the great coral reefs of recent
and modern times. Stromatolites became rare during the Cambrian with
the advent of multicellular grazing animals from which they have
little natural protection. Modern examples occur only in protected
environments such as high salt lagoons where animals don't exist (e.g.
the famous Shark's Bay examples in Australia), and in sand fields
(such as in the photograph to the left taken in the Bahamas) where
they are periodically covered in sand, denying access to grazing
animals.
Stromatolites are columnar or dome shaped finely layered structures
made up of mineral deposits resulting from bacterial community growth.
In modern stromatolites the living portion of the stromatolite is a
complex ecological community dominated by filamentous cyanobacteria on
the thin, surface, photosynthesizing, layer, with thicker, anaerobic
layers underneath. As the bacteria grow sand and other particulate
matter is trapped in the mat, along with calcium carbonate deposits,
to make up the mineralized structure. The bacteria migrate upward to
maintain access to light and food, gradually building the mineralized
stromatolite below. Ancient stromatolites have fossil remains of
cyanobacteria-like organisms which appear identical to their modern
descendants."
http://www.humboldt.edu/~natmus/Exhibits/Life_time/PreCam.web/
Also, more ideas...
"The oldest actual fossils of bacteria date back 3.5 billion years,
about 350 million years after the earliest chemical signs of life.
These fossils, discovered in the 1970s in western Australia, consist
of delicate chains of microbes that look exactly like living
blue-green algae (otherwise known as cyanobacteria). For billions of
years, these bacteria formed vast slimy carpets in shallow coastal
waters; by 2.6 billion years ago they had also formed a thin crust on
land."
http://www.pbs.org/wgbh/evolution/library/03/3/text_pop/l_033_28.html
Therefore, after all of this, I'm going to go with...cyanobacteria,
most likely algae. However, I did want you to know the other ideas and
options.
Mr. Welsh provided all of these links to me.
If this answer requires further explanation, please request
clarification before rating it, and I'll be happy to look into this
further. However, being that there are so many ideas on this topic,
and scholars cannot even put there finger on it, there is no
conclusive proof or fact of one specific animal.
Nenna-GA
Google Answers Researcher |
