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Author Topic: How Is A Fossil Formed ?  (Read 15229 times)

Offline neilep

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How Is A Fossil Formed ?
« on: 10/05/2008 17:10:55 »
Dear Fossilologists,

See these fossils ?




We all may take it for granted as to how fossils are formed but just to set the record straight...could a 1st Class geologist answer this (Bass ?)...if not....can a 3rd class-as -old-as-a-fossil Geologist answer (JimBob ?)

I mean..I know that fossils are made in a factory and sold to shops and market traders for retail....but ...an informed accurate explanation would be most welcome.

Thank Ewe.




 

Offline neilep

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How Is A Fossil Formed ?
« Reply #1 on: 11/05/2008 21:09:46 »
Atchooo !!


ooops.....accidentally sneezed here.....good job there are NO posts to cover in  green smegma !!
 

Offline Karen W.

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How Is A Fossil Formed ?
« Reply #2 on: 11/05/2008 21:49:00 »
I thought fossils were formed by animals shells or objects that have been covered over the years with dirt mineralls and the layers have built up around them and baked in the sun and elements for so long they become encased inside thus preserving some objects and forming a mold around objects.. but it seemed that there was some other points I can't remember.. the exact process and conditions..
 

Offline Karen W.

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How Is A Fossil Formed ?
« Reply #3 on: 11/05/2008 21:51:19 »
Atchooo !!


ooops.....accidentally sneezed here.....good job there are NO posts to cover in  green smegma !!

Bless you...Poor Sheepy Baby... getting a bug!

Hope you feel better now wipe your nose.. drink plenty of fluids.. And wheres the lysol??
 

Offline Bass

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How Is A Fossil Formed ?
« Reply #4 on: 11/05/2008 23:40:24 »
I'm impressed Neil!  You can sneeze and leave those impressions on rocks? ??? ;D 
You've uncovered paleontology's dirty little secret.

My wife calls me her 1st mate- with no hope of promotion......- but I've never made it to the rank of 1st class (flattery will get you everywhere). 

Only the lucky few (way less than 1%) ever become fossils.
Most fossils are form something like this (permineralization):

1.  The organism dies.
2.  The organism's remains do not decay, nor are they consumed by scavengers
3.  The remains fall, or in the case of marine organisms, settle into soft sediments
4.  Continued sedimentation buries the remains.
5.  The remains may decay, leaving only the hard parts.
6.  Lots of time (millions of years), continued sedimentation and pressure change the surrounding sediments into rocks.
7.  The cellular openings and/or the hard parts are replaced by minerals.  Mineral-rich water dissolves the organic remains and replace it with calcite, silica, pyrite or other minerals.
8.  The rocks are uplifted, eroded and the fossils are exposed for your viewing pleasure.

In the case of your pictures, this is the less common carbonization (or distillation) process, where the organism totally decays during burial, leaving only carbon behind- very detailed, yet delicate, impressions are left behind in the rock. 

Even less common are fossils in amber (tree sap- of Jurassic Park fame), mummification (dessication), freezing, and unique circumstances, like tar pits.

Basically the organism has to die, be quickly buried, lithified over millions of years, then exposed- in that order (you're safe Neil, exposing yourself to the neighbors will not turn you into a fossil).

The 3rd class curmudgeon of whom we are all so fond is much more competent in this area of geology and will no doubt contribute to this thread!
« Last Edit: 11/05/2008 23:46:58 by Bass »
 

Offline JimBob

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How Is A Fossil Formed ?
« Reply #5 on: 12/05/2008 00:53:40 »
I'll be horsewhipped if I will answer questions from people who insult me. It just isn't right!

HUMMMMMMMMMM .........

But today is also Mother's Day in the U.S. so in memory of my sainted mother, I will forgive you all.

Yeh, verily ye are forgiven for you know not what you do.


So here is the CORRECT answer, Bass. 

(Living with Snow White and working our mine I got the name Grumpy - I don't know why but that has stuck.)

There are several types of fossils:

Molds, casts, impressions with part of the original animal material included, preserved fossils, replacements, recrystallizations, and trace mark fossils.

Molds are the outer shape of a beasty that has been preserved as a stone. It is like taking an impression of something and having that preserved in the rock. 

A cast is a fossil that has been formed when something, such as a snail, has its insides filled with mud and the shell is dissolved, leaving a cast of something. A similar modern example are those silly figurines women like to put on shelves of ladies in fancy dresses cast in porcelain and painted colorfully.

Impressions with part of the original animal material included. The critter on the right in Neil's picture is such a fossil. Part of the shrimp-like beast is still there but more of the beastie than the preserved material can be seen so these are impressions. What is preserved are the keratin parts as well as the soft parts of this animal.

Impressions are just casts and are included with them. Some of the oldest fossils know are of this type. They are just impressions in shales or fine sandstones of the soft parts of criters we can't even  imagine these days.

Preserved fossils are the type Bass described and include dinosaur bones and things like the oyster shells found around Austin in the limestones, Exogyra - (curled) oysters of several types, Inocermous bivalve shells, etc.

Replacement and recrystallization fossils are preserved shells, wood, leaves and some of those same oysters. In a shale that occurs below one large limestone layers around here, the Del Rio Shale, there are Exogya arintina that have been replaced by pyrite and are quite pretty. I have some packed away (I still haven't got all my junk unpacked) or I would take a picture an post it. Also in this class of fossils are the trees of the petrified forist which have been replaced with silicate minerals, mostly agate and some opaline minerals. It is the opaline minerals that gives the wood fossils the sparkling colors.

Trace or trace-mark mark fossils are things such as dinosaur foot prints and shrimp burrows, worm burrows, crab warrens, some that are obviously communal in nature, and other indirect evidence of a life form. There are many types seen all throughout the geologic record. The oldest known fossils are of this type. Cyanobacteria (also called blue-green algae) form stromatalites such as those seen in the oldest rocks with life traces in Australia. These fossils form when mud is caught between the little bacteria as the grow and are trapped in a matrix. Color changes in mud types cause color changes in the preserved mud mounds. The oldest stomatalite is thought to be ~3.6 billion years old. Pictures of living stromatalites can bee seen at http://en.wikipedia.org/wiki/Stromatalite

Having said all of that, there is considerable variation between all of these fossil types - dinosaur bones can be replaced with silicates, etc. These fossil types should be considered endpoints in the types of fossils. There are variations of all sorts between these end points that make mixed fossil types.


Thus endeth the homily - Vicar JimBob
« Last Edit: 12/05/2008 15:23:07 by JimBob »
 

Offline JimBob

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How Is A Fossil Formed ?
« Reply #6 on: 12/05/2008 04:37:51 »


You know, I got to thinking as I reclined reading my new book this evening:

SOME ore bodies are also fossils, Bass. You overlooked these very important fossils without which this economy  - NAY, I dare say THE TOTALITY OF THE WORLD'S PRESENT CIVILIZATION, could not exist.

I think it somewhat disturbing that you should have overlooked this. This fact and the following examples of fossils, Bass - actual ores (no pun intended) - are supposedly your area of expertise.  HANG YOUR HEAD IN SHAME !!!!!

The example that came to mind are the pre-Cambrian banded iron ores produce by stomatolitic entrapment, then folded and metamorphosed. (The metamorphism and folding is unnecessary for these deposits to qualify as ores.)

Also, an example that then occurred to my incisive intellect (the child of my massive genius) and which is sometimes not metamorphosed, is coal. It is not specifically an ore but it IS part of the mining geology curriculum, Bass. It is compacted organic material and, sometimes as well, actual tree parts, leaves, bones of animals and carapaces plus other parts of insects that were drowned or otherwise died in the swamp. Anthracitic coal is metamorphic. That is why it burns so hot - most of the chemical impurities and all of the water has been driven out of the coal. I dare say that there are other examples, such as radiolarian deposits, that are equally important fossils. Radiolarian soil and chert are crucial for many manufacturing processes. There are also others out there I am sure. I am much more interested in my book at present. I can't be bothered.


Ah, the burden of the accumulated knowledge one of mature years carries. One must always mentor the young.


   The new book I am reading (actually bought at a used book store - I read a lot) is named:


"The History of Farting"

By Dr. Benjamin Bart,

Dr, Bart is grandson of the "... late and hardly lamented Dr. Gustave Bart, Surgeon-General of the Prince of Wales Light Horse at the time of Beersheba,[*]  whose most frequently-given medical advice to soldier and setteler alike was "treat yourself to a good fart!" 
[* - Last great horse cavalry charge, Palistine, World War I, for the unenlightened - JB]

If you don't believe me (you should, but their will be doubters, I'm sure) you can look it up.

This book is published by:

Michael O'Mara Books, Ltd.     
9 Lion Yard
Tremadoc Road
London SW4 7NQ

ISBN Number 1-85479-754-9

Oh ye of little faith. I told you so.

Excerpts of this delightful little tome will appear on this forum soon. It is too delightful to keep to myself as I sit and chortle a great deal while indulging myself in this delightful little book.     

       
« Last Edit: 12/05/2008 04:52:57 by JimBob »
 

Offline Karen W.

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How Is A Fossil Formed ?
« Reply #7 on: 12/05/2008 06:58:27 »
Sounds like a funny book Jimbob!
 

Offline Bass

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How Is A Fossil Formed ?
« Reply #8 on: 13/05/2008 05:38:08 »
I bow before thee, JimBob the Neil Sedakian (soft-rocker for the non-geo-oriented)



You know, I got to thinking as I reclined reading my new book this evening:

SOME ore bodies are also fossils, Bass.  HANG YOUR HEAD IN SHAME !!!!!

The example that came to mind are the pre-Cambrian banded iron ores produce by stomatolitic entrapment

You win on coal, and I'll even spot you diatomaceous earth.

But, BIF's (banded iron formations) are fossils?


Banded iron formations may be associated with stromatolites, but that doesn't imply a causal relationship.  If there was anything else living on the shallow seafloors at that time (being but only a toddler at that time, JimBob was too young to be swimming in the ocean), they also would have been caught up in BIF's as well. 
« Last Edit: 13/05/2008 05:39:59 by Bass »
 

Offline JimBob

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« Reply #9 on: 13/05/2008 13:08:07 »


Bass, Check your sources again. You are obviously NOT up on some of the current thinking in this field - too may trees in you past. Your beginning to act like Doctor Beaver.

The lesson follows:

"Origins

The conventional concept is that the banded iron layers were formed in sea water as the result of oxygen released by photosynthetic cyanobacteria, combining with dissolved iron in Earth's oceans to form insoluble iron oxides, which precipitated out, forming a thin layer on the substrate, which may have been anoxic mud (forming shale and chert). Each band is similar to a varve, to the extent that the banding is assumed to result from cyclic variations in available oxygen. It is unclear whether these banded ironstone formations were seasonal, followed some feedback oscillation in the ocean's complex system or followed some other cycle.[1] It is assumed that initially the Earth started out with vast amounts of iron dissolved in the world's acidic seas. Eventually, as photosynthetic organisms generated oxygen, the available iron in the Earth's oceans was precipitated out as iron oxides.[citation needed] At the tipping point where the oceans became permanently oxygenated, small variations in oxygen production produced pulses of free oxygen in the surface waters, alternating with pulses of iron oxide deposition."
Reference - http://en.wikipedia.org/wiki/Banded_iron_formation

"It is theorized that the Earth's primitive atmosphere had little or no free oxygen. In addition, Proterozoic rocks exposed at the surface had a high level of iron, which was released at the surface upon weathering. Since there wasn't any oxygen to combine with it at the surface (like happens now in our oxygen-rich atmosphere), the iron entered the ocean as iron ions. At the same time, primitive photosynthetic blue/green algae was beginning to proliferate in the near surface waters. As the algae would produce O2 as a waste product of photosynthesis, the free oxygen would combine with the iron ions to form magnetite (Fe3O4), an iron oxide. This cleansed the algae's environment. As the biomass expanded beyond the capacity for the available iron to neutralize the waste O2 the oxygen content of the sea water rose to toxic levels. This eventually resulted in large-scale extinction of the algae population, and led to the accumulation of an iron poor layer of silica on the sea floor. As time passed and algae populations re-established themselves, a new iron-rich layer began to accumulate. Unfortunately, the algae were of relatively low intelligence and were unable to learn from their past excesses (this was also before the EPA), so they would again proliferate beyond the capacity of the iron ions to clean up their waste products, and the cycle would repeat. This went on for approximately 800,000,000 years!"
Reference: http://jersey.uoregon.edu/~mstrick/RogueComCollege/RCC_Lectures/Banded_Iron.html

Atmospheric oxygen built up in the early history of the Earth as the waste product of photosynthetic organisms and by burial of organic matter away from surficial decay. This history is documented by the geologic preservation of oxygen-sensitive minerals,
deposition banded iron formations, and development of continental "red beds" or BIFs. Figure from the University of Michigan's Introduction to Global Change web site."
Rerference: http://www.ux1.eiu.edu/~cfjps/1400/atmos_origin.html

"Alternatively, or in addition, both iron and silica may have been derived from submarine magmatic and hydrothermal activity. Under calm, shallow marine conditions, the iron in seawater combined with oxygen released during photosynthesis by Cyanobacteria (primitive blue-green algae, which began to proliferate in near-surface waters in the Paleoproterozoic) to precipitate magnetite (Fe3O4), which sank to the sea floor, forming an iron-rich layer.
Reference: http://www.enotes.com/earth-science/banded-iron-formation

"Banded Iron Formation (also known as BIF) is a term that is applied to a very unique sedimentary rock of biochemical origin. These rocks are unique in their make up, unique in their age and unique in their origins.  They are found all over the world, but only in certain areas of all the major continents.  Every continent has a BIF formation."
Rference: http://www.galleries.com/Rocks/bif.htm

All of these references are in the mains stream. SO, whether by stomatolitic or plain old iron fixing due to the cyanobacteria, they are still trace fossils of life forms.

NEED I CONTINUE?

It would be wise, oh young padawan, to keep up with the literature - it is part of the duties of the scientist.

The Master has spoken.

 
 

Offline Bass

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How Is A Fossil Formed ?
« Reply #10 on: 13/05/2008 18:41:27 »
According to your reasoning, all stratiform mineral deposits are "fossils".  Wishful thinking.

Certainly the sudden availability of oxygen created BIFs, and there is no doubt that oxygen was produced biogenically.  But, BIFs formed through chemical reactions (see your citations), not necessarily by direct biological reactions.  Next you'll be claiming that all sandstones are fossils, since free oxygen in the atmosphere, created biogenically by photosynthesis, chemically weathered granitic rocks forming the sand grains.

Fossil:
Dictionary of Geological Terms (AGI):  An impression, cast, outline, or track of any animal or plant that is preserved in rock after the original organic material is transformed or removed.

Are coal beds considered fossils?  Absolutely!
Are BIFs considered fossils?  Absolutely not!

Quote
The Master has spoken.

Master Fossil may have spoken, but I believe he's spent far too many years sniffing oil fumes.
« Last Edit: 13/05/2008 18:44:07 by Bass »
 

Offline JimBob

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How Is A Fossil Formed ?
« Reply #11 on: 13/05/2008 20:01:00 »
AT lease it wasn't in a mercury mine, where you've spent most of your time!

Back Friday - to be continued  - (3rd class curmudgeon : who does he think he is ????? 3rd class curmudgeon, my arse! Some sort of master - can't even hold a full time job as a geologist, needs to pick up blown-down trees to make ends meet. how sad.
 

Offline Bass

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« Reply #12 on: 13/05/2008 23:15:07 »
  



 

Offline JimBob

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How Is A Fossil Formed ?
« Reply #13 on: 17/05/2008 00:44:34 »
According to your reasoning, all stratiform mineral deposits are "fossils".  Wishful thinking.

Quote
The Master has spoken.

Master Fossil may have spoken, but I believe he's spent far too many years sniffing oil fumes.

Really? Wishful thinking?

Is not the generation of oxygen by a biological agent an activity without which the banded iron ores would not have formed?

 

Offline Bass

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« Reply #14 on: 17/05/2008 02:52:31 »
I've already agreed that oxygen was generated by biologic activity...

Certainly the sudden availability of oxygen created BIFs, and there is no doubt that oxygen was produced biogenically. 

However, iron precipitation was not the result of direct biologic activity; rather it was caused by a simple chemical reaction (regardless of how the free oxygen was formed).
On the other hand, I would consider framboidal pyrite in shales to be fossils, since it is precipitated by direct biological (most likely bacterial) activity.
(btw- the 3rd class comment was first bleated by the 4 legged wool-bearer- I was merely being agreeable)
 

Offline JimBob

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« Reply #15 on: 17/05/2008 17:18:27 »
Well, then we geniuses are in accordance as I will concede the point to the co-grand master of Geo-bushido.
 

Offline Alandriel

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How Is A Fossil Formed ?
« Reply #16 on: 17/05/2008 18:06:27 »
.... sneaks in..... leaves a huge plate of CHOCOLATE cookies......

sneakes out



LOVE this thread !   ;D
 

Offline Bass

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« Reply #17 on: 17/05/2008 22:22:15 »
.... sneaks in..... leaves a huge plate of CHOCOLATE cookies......

sneakes out


Looks around guiltily, brushing off crumbs and wiping chocolate from chin, mutters to self...  I can't believe I ate the whole plate.
 

Offline JimBob

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« Reply #18 on: 18/05/2008 02:16:27 »
Didn't your mother teach you to share, little piggy?

Alandriel, thank you for the thought and consideration. But there are some barbarians out there. Attila the Pun ate the whole plate of cookies - and considering the evidence left - the plate itself as well. It is a shame that not even a good education can civilize some people. We must just bear this travesty in silence and with forgiveness in our heart.


 
 

Offline rosalind dna

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How Is A Fossil Formed ?
« Reply #19 on: 18/05/2008 13:01:23 »
I wonder what fossilised Choccy biscuits would look like that
is if we've any left. There won't be in my home.
 

Offline JimBob

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How Is A Fossil Formed ?
« Reply #20 on: 19/05/2008 00:08:22 »
They are called by the name "coprolite" - look up the word.
 

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How Is A Fossil Formed ?
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