This indicates that the rate of DNA decay can vary widely from sample to sample due to various environmental factors. For instance, the DNA degradation rates in the moa bones were found to be nearly times slower than predicted from published kinetic data of in vitro DNA decomposition. Thus, it is not clear that these relative short-term less than years old results with bird bones in a limestone setting necessarily predict the fate of DNA in other specimens, such as the much larger dinosaur bones which were deposited in sandstone. As another example of the longevity of DNA under some conditions, fragments of mitochondrial DNA, long enough to sequence, have recently been recovered from a , year old hominin fossil [20].
These factors include isolation within tiny pores in the bone, association with the bone mineral, the tertiary structures of the proteins, and the role of iron in promoting cross-linking. In the mineralized matrix of bone, many factors converge to alter the dynamics of cell death and degradation, ultimately contributing to disruption of the degradation pathway.
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For example, necrotic or apoptotic cells are rapidly destroyed by phagocytosis or by microbial attack post-mortem, but osteocytes are inaccessible to other live cells, which may, in part, explain their preservation in these ancient tissues. Second, osteocytes are inherently resistant to degradation because location within the bone matrix inhibits cell division, therefore cells may be required to last the lifetime of the organism. Osteocyte expression of apoptotic repressor proteins may also contribute to their persistence.
The association of actin with alpha-actinin and fimbrin confers stability to actin over the lifetime of the cell and may also stabilize the protein after death. Finally, osteocytes have limited access to oxygen within the bone matrix, and may thus be protected from oxidative damage.
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Cell death, whether by apoptosis or necrosis, is quickly followed by autolysis, which normally destroys the cell and releases autolytic enzymes into the surrounding environment. Autolysis, however, is self-limiting, and after reaching a certain threshold, the remaining cells are stable for long periods. The association with mineral affords other protections that are unavailable to non-biomineralized tissues and cells. The microcrystalline surfaces of apatite may act like clay grains, adsorbing degradative.
Iron is a reactive oxygen species ROS , and this switch triggers the formation of hydroxyl radicals Through a cascade of events referred to as Fenton chemistry highly reactive hydroxyl radicals trigger both crosslinking of proteins and peroxidation and crosslinking of the fatty acids making up cell membranes Because osteocytes are intimately linked through filopodia to the vascular system of bone and because the iron-binding protein ferritin has been identified in this cell line they would be susceptible to this chain reaction.
Iron may also function to bind oxygen, preventing oxidative damage to tissues and molecules. In another study, Schweitzer, et al. After an animal dies, the iron from the hemoglobin in their red blood cells can be released to interact with other tissues. Using an array of analytical techniques, they observed iron-rich nanoparticles as being intimately associated with the preserved flexible vessel tissue recovered from the bones of T.
The high-magnification image below shows inorganic iron-rich nanoparticles associated with the organic layer of the vessel of a T. In this image the iron particles appear to be concentrated on the outside of the vessel. The duckbill vessel tissue see Figure 1 b of Schweitzer, et al.
Carbon dating dinosaur bones
It seems likely to me that the iron was originally more finely dispersed and more available to do chemistry, and later precipitated into these nanoparticles. Direct contact with iron or iron particles, as with direct contact with bone mineral, can assist in tissue stabilization. In these images, internal cellular features like chromatin and nuclear membrane were visible in ostrich tissue, but not in the dinosaur structures, which is consistent with substantial degradation of the internals of the dinosaur cells.
Some ostrich vessels were incubated in a solution of hemoglobin. This hemoglobin had been extracted from the red blood cells of chicken and ostrich blood, and then re-diluted to its original concentration in the avian blood. The vessels sitting in hemoglobin solution have shown no signs of degradation for more than two years. In contrast, the ostrich vessels in plain water or phosphate buffered saline PBS showed significant degradation within three days, i.
These results dramatically demonstrate the efficacy of iron-based tissue preservation, which has not generally been taken into account in earlier estimates of how long proteins can survive. Ostrich blood vessels incubated for 30 days at room temperature under oxygenated conditions, with B or without D added hemoglobin in the incubation solution. From Figure S5 of Schweitzer et al.
A study by Boatman, et al. Initial infrared spectroscopy suggested the presence of highly crosslinked collagen within dinosaur fossil tissue. Both of these reactions depend on the oxidation potential of iron. To test the roles of these mechanisms, they incubated fresh, demineralized chicken bone using corresponding treatments to induce collagen crosslinking.
Dinosaur Soft Tissue
Analytical results showed that these treatments did indeed induce the type of crosslinking which is expected to make the collagen more resistant to decomposition. Also, the preserved dinosaur tissues were found to be sufficiently crosslinked to withstand a chemical which cleaves lightly-crosslinked molecules:.
Fossil vessels treated with the reducing agent [NaBH4, which can cleave low-order intermolecular crosslinks] yielded no significant changes in FTIR analysis, suggesting that the non-enzymatic crosslinks formed in this tissue are irreducible. Such bond formations occur between three or more peptide strands, and as such, tend to be highly resistant to reductive cleavage. As might be expected, young earth creationists have taken these observations of soft tissue from dinosaur bones as evidence that these fossils cannot be more than a few thousand years old — and therefore, conventional geological methods like radioactive dating must be terribly flawed, since these methods show the rock layers entombing these fossils as being about 70 million years old.
I cited a couple of these young earth articles at the beginning of this article. Some of these sites misrepresent the facts, stating that actual red blood cells have been found. As noted above, that is not the case: The actual organic remains are highly crosslinked remnants of a several proteins which are known to have stable structures.
These remnants retain the shape of the original soft tissue, which is not surprising, since they were confined within tiny pores in the dinosaur bones. The main attack by young earth creationists on the antiquity of these finds is an argument from incredulity, based on ignorance: Yes, experiments on protein degradation in test tubes indicate that proteins would break down completely within about a million years.
But lots of examples show that the rate of protein degradation varies wildly, depending on the conditions, so no one can say with certainty how long some fragments of protein can last, preserved with iron and sealed in mineral pores. It is difficult to devise definitive experiments to mimic that timespan. The ostrich vessels discussed above had their lifetime before degradation extended from three days to more than two years, a factor of over We can even see widely differing decomposition rates in our food, depending on how it is treated. If you leave a jug of milk on the counter for two weeks, lots of biochemistry will take place mainly lactose fermentation to acids but also including protein degradation which may render it unfit for human consumption.
However, if the milk is contacted with the right bacteria and other materials, the milk proteins can be preserved in the form of cheese which can sit stably on the shelf for years. Similarly, if beef is ground to hamburger and left in a package on the counter for a week, it will rot. However, if the beef is sliced thin and dried to jerky, it will last for months. Same milk and same beef, but with a different set of conditions they can retain proteins for ten or a hundred times longer, depending on their circumstances.
From studies like there, we know that the flesh and skin can decay off a human in about a month under humid conditions. Thus, it is absurd to say that because proteins disappear in a million years under one set of conditions, therefore protein remnants could not endure for more than million years under some other conditions. Since that claim in one form or another is at the heart of the young earth interpretation of these fossil tissues, the young earth case here collapses. We may contrast the uncertainties regarding biological decay, to certainties regarding the physical decay of radioactive elements.
These decay rates have been measured in many laboratories in many ways for many years, and they are essentially invariant. There are some particular circumstances where radioactive decay rates can be accelerated, but these are well-understood within the framework of physics. For instance, in a nuclear reactor or bomb, an artificially high density of uranium means that the neutrons from one splitting nucleus have a high probability of striking another nucleus and causing it to split.
Research illuminates inaccuracies in radiocarbon dating
However, these effects are understood and predictable. Since radioactive dating militates for an old earth, of course young earth creationists will not concede to its validity. They advance various objections, but these objections have been refuted over and over again by practicing scientists.
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For instance, see these resources:. What evidence is there for the earth being billions of years old? Radiometric Dating Does Work!
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Delves into several detailed examples, including the Hell Creek formation. For my part, I have documented the errors of young earth arguments regarding the dating of Grand Canyon rocks , and the dating of some recent lava flows. I have also compiled some other physical evidences e. It would be tedious to retrace all those prior discussions. Thousands and thousands of radioactive dating measurements have been made, so naturally there will be a few that give anomalous results. For many of these cases, it can be seen why the results were odd — for instance, the rock sample may have been re-heated after it initially solidified, which partially re-set the atomic clock.
However, the RATE scientists did not find any actual evidence of faster radioactive decay; they simply asserted that there MUST have been accelerated radioactive decay, in order to meet their existing young earth model. They presented no valid physical support for this. They rehashed four arguments against conventional old-earth dating, but these arguments have been thoroughly debunked by practicing scientists [36]. To overturn the last hundred years of physics would merit a legitimized platform to tell the world at large that old-earth dating methods are unreliable.
It might even merit a Nobel Prize. The standard young earth creationist excuse for not doing this is: Young earth geologists have been allowed to present a number of papers and to lead field trips at recent meetings of the secular Geological Society of America, so it is in fact possible to get a hearing among geologists for an unusual perspective, as long as there is solid supporting data. This change in fauna has been obvious for over a century. Many independent radiometric measurements have been made on these tektites, consistently showing them to be around million years old.
Although the exact mechanism of the catastrophe is not clear, it is widely thought that this meteorite strike is tied to the mass extinctions of some three-quarters of plant and animal species on Earth, including all non-avian dinosaurs, which occurred at that time. The dark band in this photo indicated by the white arrow is the Z-coal, marking the top of the Hell Creek formation in Montana.
Museum of Paleontology, U. There are some bentonite clay layers within this coal bed, which incorporate minerals from contemporary volcanic ashfalls.