Table 7.

Different Types of Potential In Situ and Remote Biosignatures

	Type	Biosignatures	Examples	Appropriate techniques
In situ	Visual biosignatures	Direct observation of active life	Cellular structures (possibly seen to be motile or reproducing)	Microscopy or macroscopic imagery
		Fossils	Fossilized cells
		Artifacts of life	Stromatolites or endolithic microborings
	Chemical biosignatures	Biological macromolecules	Proteins or nucleic acid polymers (e.g., DNA, RNA)	Gas chromatography–mass spectrometry, Raman spectroscopy, X-ray spectroscopy
		Molecular fossils	Breakdown products of biomolecules, such as hopanoids or steranes
		Molecular evidence of metabolism	Biogenic biases, such as isotopic fractionation or homochirality
		Thermodynamic or kinetic disequilibrium within environment	Gradients of redox species in column of lake water
		Biominerals	Certain silicate, carbonate, or iron minerals, or metal enrichments of, e.g., Cu, Mo, Ni, W
Remote	Spectral biosignatures	Large-scale environmental disequilibrium	Atmospheric disequilibrium, e.g., O2 and CH4	IR and visible spectroscopy
		Photosynthetic life	Red edge of vegetation
	Spatially resolved	Geometrical structures of intelligent life	Roads, cities, agriculture, large-scale landscape modification	Optical imaging
	Electromagnetic emissions	Intelligent broadcasts	Radio or optical signals from a civilization	Radio or optical sky surveys