Have any deeper living organisms ever been found?
In 2021, researchers recovered microbial cells and DNA from rocks retrieved from a depth of 4,850 m below the surface.1 The New Scientist covered this finding in an article titled "Deepest land microbes ever found".
Dong and Huang say that, to the best of their knowledge, these are the deepest known microbes ever found on land. Demonstrating that the cells are living will be a challenge as microbes that live deep below the surface often operate on such a slow timescale that they show few typical signs of life such as movement or reproduction.
But there are reasons to suspect the microbes may be alive. Most importantly, they are intact rather than just cell fragments, which might hint they are carrying out basic cellular repair.
- Dai X, Wang Y, Luo L, Pfiffner SM, Li G, Dong Z, Xu Z, Dong H, Huang L. Detection of the deep biosphere in metamorphic rocks from the Chinese continental scientific drilling. Geobiology. 2021 May;19(3):278-291.