SUMMARY: Tiny (25-300 nm) objects, thought to be tiny bacteria (hence the name nanobacteria) have been found in many different types of samples, both organic and inorganic. It’s still debated whether or not these objects are actually bacteria/biotic things. This study looked at objects found on the surface of a meteorite with a transmission electron microscope in order to figure out what they were. Turns out, these objects were not bacteria or nanobacteria, but tiny crystals of calcite with a shapeless thin layer made of the same material.
LESSON COMMENTS: There is a paragraph in this article that talks about the 5 criteria for something to be bacterium; however, the following paragraph states that the objects in question are not bacteria, despite fulfilling all 5 criteria. There are many conversations and discussions that can come from this one section: characteristics of life, scientific method, and biases in science (even in a primary source)!
K. Benzerara, N. Menguy, F. Guyot, C. Dominici, and P. Gillet, “Nanobacteria-like calcite single crystals at the surface of the Tataouine meteorite,” Proceedings of the National Academy of Sciences, vol. 100, no. 13, pp. 7438–7442, 2003.