DNA is too fragile to survive more than a few hundred thousand years
The core idea stands, but key numbers or details have changed.
TaughtDNA begins breaking apart the moment an organism dies. Even in the best-preserved permafrost fossils it degrades into unreadable fragments within a few hundred thousand years, so anything a million years old is far beyond reach; forget sequencing a creature that ancient.
NowIn February 2021, researchers reported in Nature that they had sequenced DNA from mammoth teeth frozen in Siberian permafrost for more than a million years, including one specimen around 1.6 million years old, shattering the previous record held by a roughly 700,000-year-old horse.
What actually happened
DNA really does decay, and that was the basis for the old ceiling. Chemical models and the best real samples suggested that even under ideal cold, dry conditions, recoverable sequence gave out somewhere under a million years. The oldest genome anyone had read came from a horse bone dated to between 560,000 and 780,000 years, and that already felt near the limit.
The mammoth teeth broke through it. Preserved deep in permafrost and analysed with modern sequencing that can stitch together tiny, damaged fragments, three specimens (nicknamed Krestovka, Adycha, and Chukochya) yielded genomes, the two oldest well past the million-year mark. The Krestovka mammoth even turned out to belong to a previously unknown genetic lineage.
This is an update to a limit, not the overthrow of a principle: DNA still degrades, and there is still some ceiling out there. But the specific number your textbook implied, that a million years was simply too old, was wrong, and the record has kept creeping backward since.
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Who was taught this
Still standard through 2021, so anyone who finished school between 1950 and 2021 learned the earlier version.