Rhynie Chert: Botanical Significance
The Significance of the Rhynie Plants
At the end of the Silurian there began a rapid burst of evolution in plants. Within just 25 million years during the Devonian period, recognised as being one of the two intervals of greatest expansion in plant evolution, land plants evolved complex vascular systems, leaves which specialised in photosynthesis, and roots and stems for support. Most significantly sporangia were developed and seed-bearing plants evolved. More over, the biochemical and physiological processes required to support such complex organisms also developed.
The exceptional preservation of the flora in the Rhynie chert provides botanists and palaeobotanists with a unique window of a time early on in this period of rapid evolution, about 400 million years ago, during the Early Devonian. It gives scientists an insight into the morphology and detailed internal anatomy of these early land plants (in fact in some cases cellular preservation is so exquisite, that the anatomy of a number of the Rhynie plants, for example Rhynia gwynne-vaughanii and Aglaophyton major, is better known than many living plant species!). The Rhynie plants also provide clues as to the probable evolutionary pathways that gave rise to modern plants and also the mechanisms by which plants adapted to terrestrial habitats.
The Significance of the Rhynie Prokaryotes
Another reason the Rhynie chert is important to palaeobotanists, botanists, and life and earth scientists in general, is the presence of fossilised bacteria and cyanobacteria, some of which may have been thermophyllic, thriving within hot springs and their outflow channels.
Prokaryotic organisms provide a fascinating glimpse of the beginnings of life on Earth. Many modern mycoplasms (organisms related to bacteria, but of simpler structure and smaller size) are capable of independent existence and are probably very similar to the first living things. Anaerobic bacteria may resemble organisms which lived when free oxygen was not available. Cyanobacteria, being aerobic must have evolved as oxygen began to diffuse into the atmosphere. Once oxygen was available, cyanobacteria would have been responsible for increasing its concentration as a bi-product of photosynthesis.
Certain types of bacteria found in modern hot springs thrive in boiling water, in alkaline and even highly acidic waters, and many cyanobacteria tolerate temperatures up to 73oC. As such, the study of these organisms living in extreme conditions in hydrothermal areas, and their fossilised forms in the Rhynie chert, is not only important in understanding how life evolved on Earth but may also have implications for future studies in the search for life on other planets.