Plant Fossil

Stop 2 provides further insight into the terrestrial life which would have accompanied the early tetrapods. Here a number of fossilised plant stem fossils are found within a pale green siltstone unit. These stems are all aligned in the same direction indicating that they were transported and deposited by flowing water, likely as part of a river channel. The black colour of the fossils is due to carbonisation, a process in which only the carbon of an organisms remains after it has been subjected to great heat or pressure over time. 
The plant is likely Archaeopteris fissilis. Archaeopteris was one of the first trees on Earth and was widespread during the Devonian, being present from the equator to near the poles. Archaeopteris fissilis was the earliest form of this tree and would have had spiky pine-like leaves. Over time, these leaves evolved to become increasingly webbed and came to resemble the leaves of ferns that we are familiar with today. These trees are believed to have grown up to 30m high and would have grown along the riverbanks of this area. Archaeopteris became extinct in the early Carboniferous around 350 million years ago.
Archeopteris and early land plants likely played a big role in in altering Earth’s climate and environment. The development of the first major root systems impacted soil chemistry and stabilised soil.  The uptake of carbon dioxide and release of oxygen by these plants is also believed to have had major impacts on the Earth’s atmospheric conditions. Decreasing carbon dioxide levels had a feedback on global temperature and resulted in widespread cooling. 
