DNA has a 521-year half-life OCT 10 2012
Researchers in Copenhagan and Perth used DNA found in the leg bones of the extinct moa bird to determine the half-life of DNA: 521 years.
By comparing the specimens' ages and degrees of DNA degradation, the researchers calculated that DNA has a half-life of 521 years. That means that after 521 years, half of the bonds between nucleotides in the backbone of a sample would have broken; after another 521 years half of the remaining bonds would have gone; and so on.
The team predicts that even in a bone at an ideal preservation temperature of -5 ºC, effectively every bond would be destroyed after a maximum of 6.8 million years. The DNA would cease to be readable much earlier -- perhaps after roughly 1.5 million years, when the remaining strands would be too short to give meaningful information.
That means no real-life Jurassic Park, folks.