So, after seeing this I ended up searching about how good is wood preservation with age:

Normally, when wood is buried it decays rapidly. However, if the burial environment is very wet it can be preserved for centuries. Bacteria and fungi will still degrade the wood, but when the oxygen supply is limited - under wet or waterlogged conditions - this process is much slower than in the air or in a well aerated soil. https://historicengland.org.uk/listing/what-is-designation/heritage-highlights/wood-survive-underground-for-thousands-of-years