generate mutants or transgenic lines : plasmids containing transgenes are inserted into the cells using the biolistic method or transkingdom bacterial conjugation (with 10−6 and 10−4 yield respectively), and other classical transfection methods such as electroporation or use of PEG have been reported to provide results with lower efficiencies. Transfected plasmids can be either randomly integrated into the diatom's chromosomes or maintained as stable circular episomes (thanks to the CEN6-ARSH4-HIS3 yeast centromeric sequence). The phleomycin/zeocin resistance gene Sh Ble is commonly used as a selection marker, and various transgenes have been successfully introduced and expressed in diatoms with stable transmissions through generations, or with the possibility to remove it. Furthermore, these systems now allow the use of the CRISPR-Cas genome edition tool, leading to a fast production of functional knock-out mutants and a more accurate comprehension of the diatoms' cellular processes. Human uses Paleontology Decomposition and decay of diatoms leads to organic and inorganic (in the form of silicates) sediment, the inorganic component of which can lead to a method of analyzing past marine environments by corings of ocean floors or bay muds, since the inorganic matter is embedded in deposition of clays and silts and forms a permanent geological record of such marine strata (see siliceous ooze). Industrial Diatoms, and their shells (frustules) as diatomite or diatomaceous earth, are important industrial resources used for fine polishing and liquid filtration. The complex structure of their microscopic shells has been proposed as a material for nanotechnology. Diatomite is considered to be a natural nano material and has many uses and applications such as: production of various ceramic products, construction ceramics, refractory ceramics, special oxide ceramics, for production of humidity control materials, used as filtration material, material in the cement production industry, initial material for production of prolonged-release drug carriers, absorption material in an industrial scale, production of porous ceramics, glass industry, used as catalyst support, as a filler in plastics and paints, purification of industrial waters, pesticide holder, as well as for improving the physical and chemical characteristics of certain soils, and other uses. Diatoms are also used to help determine the origin of materials containing them, including seawater. Nanotechnology The deposition of silica by diatoms may also prove to be of utility to nanotechnology. Diatom cells repeatedly and reliably manufacture valves of various shapes and sizes, potentially allowing diatoms to manufacture micro- or nano-scale structures which may be of use