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We find a lot of fossils today and I have heard it is because there were different events that caused animals and dinosaurs to die. Why didn't the fallen bodies of the dead animals just rot? Why did they turn into fossils if they just fell down dead? If all of those dead animals that are fossilized were buried rapidly with water, etc., (which is needed for the fossilization process) what caused that to happen with all of the thousands upon thousands of fossilized creatures? Was it thousands of small disasters with water, etc? I'm just confused on that subject because we find so many different fossils in so many layers.

Why were bones of an iguanadon, mastadon, hadrosaurus, monkey, bison, racoon, Indian jawbone and teeth, all found together, and in the same layer in the Ashly Beds in South Carolina if they all were said to have lived at different time?

Question Date: 2014-10-23
Answer 1:

The bodies don't necessarily rot because they become buried quickly or covered. Sometimes they did rot for a few days, and were eaten by scavengers, and then buried in mudslides. This stops the rot and results in fossils after a very long time. You are exactly right: it was thousands of random events like dust storms or floods or mudslides that caused the fossils. It sounds like a lot of random chance and it is, but over millions of years there will be millions of little burials like that. You've also figured out one of the barriers to perfectly knowing every organism: some by chance never were buried by those events. When people criticize evolution and say we don't have some missing links, which may be true. But that doesn't mean they never existed, we just haven't found them yet or they were never randomly buried by chance. So it's a bad criticism of science.

The Ashley Beds appear as a common criticism of science in that they say dinosaurs and people lived together. First, I want to explain how we date bones from different animals. When an animal is alive it eats from plants that take in a certain amount of carbon 14 from the atmosphere during photosynthesis. When the animals are alive and continue to eat, they will have a constant amount of carbon 14 in their bodies. When they die, this carbon 14 stops being replaced. Because the chemical is unstable, it degrades very slowly. By measuring how much of the carbon is left, we can get a very accurate date when the animal died. So if we find a fossil that has half of its carbon 14 gone, we can see that it must have died many, many years before an animal that still has all of its carbon 14. Because we know exactly how fast it degrades we can get accurate dates. So we can show that all of these animals lived millions of years apart, rather than just looking at how deep they are.

Now, how could these things have ended up in the same layer? Think of something like the Grand Canyon. The flow of water over thousands of years has eroded down and exposed deeper and older layers of rocks. If you were to build a house in the Grand Canyon now, you would be building on older layers of rock. In the same way, sands can shift in deserts exposing different rock ages to animals many years apart. In changing environments, dating based on fossil depth is not always reliable. It is not possible that humans and dinosaurs lived together, which seems to be the suggestion by people who talk about this site. If you aren't convinced of this though, please ask what isn't clear! We know a massive amount about how species came to be, and evolution/natural selection is about as widely accepted as gravity in the scientific community. In the public though, evolution is less widely accepted than it was 50 years ago, which is not very good.

Answer 2:

These are interesting questions! You are right that if organisms just rot after they die, they will not be preserved in the fossil record. I don’t have the data to quantify this, but I suspect that a vast majority of dead organisms do just rot and do not leave fossils. Keep in mind that fossils usually do not usually contain any of the original organic material (soft parts) that made up the organism. More often, an imprint of the organism is fossilized or minerals like quartz or calcite replace body parts so that we don’t usually find the original parts.

You are also right that certain special conditions are required to preserve a fossil. If a dead organism is left exposed in the atmosphere, it may decay without leaving a trace. Rapid burial or deposition in an anoxic (without oxygen) environment may increase the likelihood of fossilization. However, it does not require a “disaster” to preserve a fossil. For a hypothetical example, suppose that a vertebrate animal dies on the edge of a riverbed. Normal rates of sediment deposition could bury the animal very quickly (in less than year).

Over geologic timescales (the earth is about 4.56 billion years old), many organisms have been preserved, even through normal geologic processes like the accumulation of sediment in basins. Concerning the Ashley phosphate deposits in South Carolina, I was unable to find an recent peer-reviewed article (an article that has been reviewed for accuracy by experts before being published) that says anything about a hadrosaur fossil being found in this location. It is extremely unlikely that a (non-avian) dinosaur fossil would be found in a Tertiary (the geologic time period after the extinction of non-avian dinosaurs) deposit. Without finding any peer-reviewed articles from the last century that report this, I cannot fully assess this statement, but I think that it is probably a mistake. It is unlikely, but possible, that a Mesozoic (the era of the dinosaurs) sedimentary rock was “reworked” in the Tertiary and that a Mesozoic fossil was redeposited in the Tertiary sediment. Even if this were the case (I suspect that it’s not), there are an overwhelming number of observations that non-avian dinosaur fossils occur in Mesozoic sediments (~250–65 million years ago), indicating that they lived, died, and were fossilized during the Mesozoic era.

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