How is it that anthrax can survive harsh conditions for years or more?

Spores: The anthrax bacteria is encased in protective little cases that can lay dormant in soil for many years before causing infections.

Endospores: The bacillus anthracis can form dormant endospores, that are able to survive in harsh conditions for literally centuries. But, when the spores are inhaled, ingested, or come into contact with a host, they often reactive, and then rapidly multiply. However, the host does have to have a lowered threshold for the organism to produce the toxin that is so deadly.