Fossils deep in earth's crust?

[Baub]

I recently read an article: The Deepest Hole by Alan Bellows, discussing the Kola Superdeep Bore Hole project. The article states.. "Another unexpected find was a menagerie of microscopic fossils as deep as 6.7 kilometers below the surface. Twenty-four distinct species of plankton microfossils were found, and they were discovered to have carbon and nitrogen coverings rather than the typical limestone or silica. Despite the harsh environment of heat and pressure, the microscopic remains were remarkably intact". How is this possible?

[insane_alien]

i'd imagine its due to tectonic plate movement. the earths crust behaves a lot like a churning semimolten plastic over geological time scales.

 

some bits get pushed up, some bits get dragged down. the top of everest is 8 km up yet it used to be a seabed seems reasonable that something could get dragged down 6km.

[Baub]

i'd imagine its due to tectonic plate movement. the earths crust behaves a lot like a churning semimolten plastic over geological time scales.

 

some bits get pushed up, some bits get dragged down. the top of everest is 8 km up yet it used to be a seabed seems reasonable that something could get dragged down 6km.

Thanks for the input. Yes, it definitely makes sense. I am aware of sea floors on mountain tops, I just did not realize a sea floor could be pulled down like that. It amazes me that, not only was it pulled down, but the plankton remained in tact. The forces being exerted on it are astounding. I am surprised the plankton wasn't ground into a fine dust.

[Mokele]

They're called 'subduction zones', where portions of the Earth's crust dive down under another plate, and are eventually melted.

 

We actually have problems finding fossils of the very earliest life because any rocks of the right age are either buried too deep to get to them, or have been melted in subduction zones.

[Baub]

They're called 'subduction zones', where portions of the Earth's crust dive down under another plate, and are eventually melted.

 

We actually have problems finding fossils of the very earliest life because any rocks of the right age are either buried too deep to get to them, or have been melted in subduction zones.

I take it then, that fossils this old are very rare? The samples from the Kola bore hole were estimated at 2.7 billion years old.

[insane_alien]

well, intact and recognisable fossils in general are exceedingly rare as the conditions necessary for fossilization to occure are exceedingly rare. the older the range your looking for the less chance of finding fossils are. the oldest are cyanobacteria from 3.4billion years ago according to wikipedia.

[Mokele]

Recognizable microbe fossils are rare anyway, and really old fossils are always rare. Think of it this way: after a fossil forms, every year it has roughly the same probability of being destroyed. As time goes by, more and more fossils from a given era are destroyed by natural forces. As a result, you have an exponential decay in fossil frequency with age. We're up to our ass in fossils from the past 5 million years, but we've only got 2 really good sites from 500 million years ago.

 

There's also hardness - the harder it is, the easier it fossilizes and the less chance of destruction. Shark teeth are dirt common, especially recent ones. Fossils of soft-bodied animals from any age, even recently, are extremely rare. And it doesn't get softer than microbes.

[CaptainPanic]

Coal, oil and gas are found up to depths of 9 kilometers (see link 1, 2) or 4000 m under the bottom of the sea (see link 3).

 

Since these fuels are "fossil" fuels, I guess it's not surprising that fossils are also found at such depths?

 

1. http://www.iht.com/articles/2006/09/05/business/oil.php

2. http://www.wired.com/cars/energy/magazine/15-09/mf_jackrig

3. http://en.wikipedia.org/wiki/Noxal_oil_field

Edited March 9, 2009 by CaptainPanic
adding another link

[Ophiolite]

Despite the harsh environment of heat and pressure, the microscopic remains were remarkably intact". How is this possible?

6.7km is not that deep. Around 22,000'. Pore pressure at this depth would be around 10,000 - 11,000psi; maximum matrix stress (the 'load' in the solid part of the rock) would be around 11,000 - 12,000psi. Since the fossils are fully embedded in the fabric of the rock - they are the fabric of the rock - then they can tolerate a lot. Pressure at this depth is mainly going to distort the shape of the fossil; the temperature, in conjunction with the pressure, is going to cause mineral changes, but that's what fossilisation is.

 

The main issue is that, if these rocks are 2.7 my old, then almost certainly these rocks were originally deeper and were subjected to higher pressures and temperatures. At 22,000' we are still probably in the realm of diagenesis. Much beyond that we are likely experiencing full blown metamorphism. That would be expected to destroy fossils, or greatly reduce their preservation quality.

 

We actually have problems finding fossils of the very earliest life because any rocks of the right age are either buried too deep to get to them

Strictly speaking the more important issues are - a)metamorphism' date=' corrupting the samples. b) microscopic character of precambrian fossils c) greater difficulty of preserving microfossils. There are plenty of old rocks at the surface in the shield areas around the world. They just suffer from points a) through c).

 

the oldest are cyanobacteria from 3.4billion years ago according to wikipedia.

I think some older ones have been found. I can't immediately put my hand on the reference. (I'm not thinking of the isotope clues from the Issua formation in Greenland.)

 

We're up to our ass in fossils from the past 5 million years' date=' but we've only got 2 really good sites from 500 million years ago.

[/quote']Hmm. I agree there are currently only a couple of sites where we have soft body parts preserved, but there are oodles of hard bodied, brilliantly preserved fossila of all kinds. Remember there were more than enough to justify the term "Cambrian Explosion".

 

And it doesn't get softer than microbes.

Absolutely.