Here’s David Tyler at Access Research Network (05/31/11), on “Non-marine life throughout the Neoproterozic”:
What do these findings mean for our understanding of life on the Precambrian Earth? Dr Charles Wellman, an author of the paper, is quoted by ScienceDaily as saying:
“It is generally considered that life originated in the ocean and that the important developments in the early evolution of life took place in the marine environment: the origin of prokaryotes, eukaryotes, sex and multicellularity. During this time the continents are often considered to have been essentially barren of life — or at the most with an insignificant microbial biota dominated by cyanobacteria. We have discovered evidence for complex life on land from 1 billion year old deposits from Scotland. This suggests that life on land at this time was more abundant and complex than anticipated. It also opens the intriguing possibility that some of the major events in the early history of life may have taken place on land and not entirely within the marine realm.”
We should note that marine organisms are isotonic with seawater: this means the same salt concentration exists inside as well as outside the cell membrane and there are no osmotic pressures. However, fresh-water and land organisms are all hypertonic, which means that the internal salinity exceeds that of the fresh-water outside the cell, and unless there are mechanisms to counter osmosis, the cell will die. In addition, non-marine life may have to face the problem of desiccation. This appears to be a real issue for some of the Torridonian eukaryotes, because some of the samples were obtained from desiccation cracks in the Diabaig Formation at Loch Diabaig (this is of personal interest, having obtained samples of these desiccation cracks some years ago from this same locality). More.