Age: early Devonian
Taphonomy is the study of what happens to an organism after it dies - how an animal becomes a fossil. The Rhynie Chert is a lagerstätte because it displays exceptional preservation of all fossils. This is the result of either the permeation of silica through organic material, or the direct replacement of organic material by silica. Often delicate internal structures are preserved.
The Rhynie Chert was part of a hot spring system, where boiling water is erupted at the surface and begins instantly to cool. This water is enriched in silica, but when the water begins to cool and evaporate, it can no longer hold the dissolved silica, and it begins to precipitate on to the nearby organisms.
In the Rhynie Chert the organisms were inundated by siliceous fluids very soon after death. The siliceous fluids permeate, or replace the organic material at a cellular level, and therefore prevent any decay from taking place. This process preserves the organisms in what is commonly known as sinter. The sinter is altered to chert as a result of high temperatures and pressures during burial.