The enzymes and cellular machinery that had maintained the genome in living tissue stopped functioning.

Bacterial activity began breaking down organic material.

The specific chemical bonds that hold the DNA double helix together began to be attacked by water molecules, by bacterial enzymes, and by the chemical radicals produced by radioactive decay in the surrounding sediment.

What slowed this degradation and allowed meaningful genetic material to survive 24,000 years was the cold — the consistent, year-round cold of the Siberian burial environment, which slowed bacterial activity and reduced the rate of chemical degradation.

The fragments of DNA that survived were short and chemically damaged, but they were readable.