How life first colonised the land is still one of the great palaeontological mysteries. Living outside of the ocean is fraught with danger: exposure to the elements, dehydration and UV radiation are but a few. The key interval under investigation is 500 - 400 million years ago. During this time interval life was well developed in the sea. 500 - 400 million year old terrestrial rocks (those deposited by rivers, lakes, soils and wind) are available for exploration and it was in these that microscopic discoveries were made in the 1980s. These discoveries were thought to be two organisms, but recent research has shown that they are infact the same taxa, just at different stages of growth. The fossils, from Sweden and Scotland, are of fungi and this may be some of the earliest organisms to extract nutrients from simple soils.
A fossil dating from 440 million years ago is not only the oldest example of a fossilised fungus, but is also the oldest fossil of any land-dwelling organism yet found. The organism, and others like it, played a key role in laying the groundwork for more complex plants, and later animals, to exist on land by kick-starting the process of rot and soil formation, which is vital to all life on land.
http://www.eurekalert.org/pub_releases/2016-03/uoc-lo022616.php
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