[SquarishTriangle (OP)]

So, some viruses (and some bacterial spores) are known to survive for long periods in the environment and be resistant to the elements. Would it be possible for a particularly hardy pathogen to land on some sediment, become incorporated into the rock as the sediment is compacted, spent thousands of years protected inside this rock in a dormant form, and then finally be released into the environment when the rock breaks apart (erodes, falls off the side of a cliff, earthquake etc.) and go on to infect a new host?

[CliffordK]

It might depend on how the rock was formed.  High temperatures, pressure, and heat involved in many forms of rock could be bad for the viability of life.

There are reports of ancient Amber (> million years) containing viable spores.

[evan_au]

spent thousands of years protected inside this rock in a dormant form, finally be released into the environment when the rock breaks apart (erodes, falls off the side of a cliff, earthquake etc.) and go on to infect a new host?

This is certainly a concern as the tundra melts - it may release new strains of disease organism that have been frozen for thousands of years.

Would it be possible for a particularly hardy pathogen to land on some sediment, become incorporated into the rock

It is unlikely that a surface-dwelling bacterium could be incorporated in rock, and continue living - the change in environment is just too great. Living things require an ecosystem in which to live, and an ecosystem would not survive such a major change.

In tough times, some bacteria (and larger creatures like tardigrades) can go into a dormant state, and then resume growth when the necessary ingredients return - water, food, temperature, oxygen (or lack of oxygen), etc.

But the Desulforudis bacterium was found in a deep gold mine
- It is found as a monoculture, ie it is its own ecosystem.
- It lives and grows in rocks, using energy from the radioactive decay of elements in the rock.
- The fact that it is killed by oxygen suggests that it is not a surface bacterium that got buried, but perhaps one that has been living out its whole existence in deep rocks. (For comparison, some anaerobic bacteria in our gut can produce spores that survive exposure to oxygen.)
See: https://en.wikipedia.org/wiki/Desulforudis

[chris]

This is a really nice interview about extreme bacteria surviving in the Atacama desert and the prospects for life on Mars. It's pertinent to this discussion.

[chris]

But the Desulforudis bacterium was found in a deep gold mine

Pursuant to Evan's post, this is me down a gold mine in South Africa looking for long-lost microbial life!