After cell death, enzymes start to break down the bonds between the nucleotides that form the backbone of DNA, and micro-organisms will speed the decay.  How long does this process take?

 

In 2012 a team of scientists from both New Zealand and Denmark worked together to study the fossilised bones of the Moa.  The Moa was a flightless bird living in New Zealand, that was made extinct by human settlers in the 13^th Century.  The teams took 158 DNA-containing leg bones, between 600 and 8000 years old, all of which had been found within 5 km of each other with nearly identical preservation conditions, including a temperature of 13 degrees C.  The age of the bones was gauged by radiocarbon dating.

 

By comparing the age of the different specimens and the degree of DNA

degradation, the researchers calculated that (under ideal conditions) DNA

has a half-life of 521 years.  This means that after 521 years, half of the

bonds between the nucleotides in the backbone of the sample would have

broken.  In another 521 years, only ¼ would be left and so on.  The team

predicted that, even in a bone at an ideal preservation temperature of -5

degrees C, all DNA would have been destroyed after a maximum of 6.8

million years.  The DNA would cease to be readable much earlier, perhaps

after 1.5 million years, when the remaining fragments would be too short to give meaningful information.

 

This is sad news for Jurassic Park.  Remember that the dinosaurs suffered mass-extinction 65 million years ago.  If current scientific thinking is correct, no DNA could have survived in fossils of any kind, or even frozen remains.