Editorial: Origins of plant life

Published in The Hindu on November 2, 2010

Evidence collected from western Argentina samples shows that land plants (Embryophytes), which played a critical role in changing the global climate and in the evolution of multicellular life, had established themselves on the dry parts of the globe about 8-12 million years earlier than previously thought. A paper in the New Phytologist journal reports that spores representing five genera were found in samples recovered from western Argentina. The spores belong to liverworts (cryptospores), the basal group of land plants that still exist and are 473-471 million years old. Similar evidence from 463-461-million-year-old land plants came from liverwort spores recovered from Saudi Arabia and the Czech Republic. The latest evidence from Argentina indicates that terrestrial plants had already diversified as early as 473-471 million years ago. Thus the most remarkable chapter in the earth’s history: the invasion of the land by plants had probably taken place during the Cambrian period, millions of years earlier than what the fossil record currently reveals. The study reaffirms the assumption that land plants had evolved in the eastern parts of the supercontinent Gondwana before the continents split millions of years ago and moved to their present positions.

The possibility of plant terrestrialisation at multiple locations at almost the same geological time appears quite unlikely. But the possibility of long-range dispersal of spores from western Argentina to Saudi Arabia and the Czech Republic in a span of 8-12 million years cannot be completely ruled out. In fact, present day western Argentina and Saudi Arabia and the Czech Republic were located in the same latitude (35° S) 470 million years ago. The spores, in turn, were also equipped for long-range dispersal, both in aerial and aquatic environments. After all, the outer cell wall of liverwort spores is covered by sporpollenin, the most resistant polymer known to man. The coating protects the spores from abrasion, ultraviolet light, desiccation and micro-organism attack. That scientists could extract the spores from samples by dissolving the rocks in acid indicates the spores’ ability to withstand chemical action. After all, such protection was necessary to survive in the harsh aerial conditions that prevailed at that time. Early land plants lacked lignified tissues that enable plant fossilisation. This makes clear that spores and pollens hold the key to the search for the earliest origins of plant life rather than plant megafossils which are much harder to recover.