Previously, only the hardiest of bacteria were able to survive in the barren, irradiated soils of the primordial continents. Yet rising levels of oxygen in the atmosphere meant that gradually the terrestrial world became increasingly habitable. The oldest signs of terrestrial ecosystems come from 410 million year old rocks in Scotland from a formation known as the Rhynie Chert. Preserved within its silica tombs are some of the earliest plants and arthropods to have lived.
From this point onwards, terrestrial life in the fossil record becomes more apparent. What is interesting is that this sudden, early colonization of the continents is recorded on one continent only. 410 million years ago, there were two landmasses on Earth: Gondwana and Laurasia. The Rhynie Chert and the various other records of these land pioneers are all found in rocks which once made up Laurasia. Our picture of how life gradually left the waters comes from this.
|The 350 million year old scorpion Gondwanascorpio emzantsiensis|
|The claw of Gondwanascorpio emzantsiensis|
Now, a find from South Africa has put Gondwana on the biological map. Earlier this year, Dr Robert Gess from the Evolutionary Studies Institute at Wits University found the remains of a scorpion in 350 million year old rocks from the Witteberg Group near Grahamstown in the Eastern Cape.
|The stinger of Gondwanascorpio emzantsiensis|
'For the first time we know for certain that not just scorpions, but whatever they were preying on were already present in the Devonian. We now know that by the end the Devonian period Gondwana also, like Laurasia, had a complex terrestrial ecosystem, comprising invertebrates and plants which had all the elements to sustain terrestrial vertebrate life that emerged around this time or slightly later,' said Gess.
Exactly why there is such a difference between when Gondwana and Laurasia were colonized is unclear. Studies have revealed that the two were separated by a deep ocean 450 million years ago. Climatic differences may also have resulted in more favourable ecological conditions. Even so, it will require more study and fossil evidence before we understand why Laurasia was the cradle of terrestrial life, while Gondwana remained a lost continent for millions of years. Yet the discovery of Gondwanascorpio, however, is a positive start.