Origin of Life: how did plants get onto land (Introduction)

by David Turell , Sunday, December 20, 2015, 01:40 (3049 days ago) @ David Turell

Think about it: if life started at sea, how did plants get up onto land. They don't have fin/legs like some fish did and do. Obviously algae could wash up on the shoreline and take hold. A new study considers how algae may have accomplished the feat:- http://www.sciencedaily.com/releases/2015/12/151216134406.htm-"Plant biologists agree that it all began with green algae. At some point in our planet's history, the common ancestor of trees, ferns, and flowers developed an alternating life cycle--presumably allowing their offspring to float inland and conquer Earth. But on December 16 in Trends in Plant Science, Danish scientists argue that some green algae had been hanging out on land hundreds of millions of years before this adaptation and that land plants actually evolved from terrestrial, not aquatic, algae.-***-"Notably, traits that land plants use to survive on land today are well conserved in some species of green algae.-***-"'We realized that algae have a cell wall that's similarly complex to terrestrial plant cell walls, which seemed peculiar because ancient algae were supposedly growing in water," says Harholt, Science Manager at the Carlsberg Laboratory. "We then started looking for other traits that would support the idea that algae were actually on land before they turned into land plants."-"Working with Moestrup, an expert in algae, they also explored structures (or rather, the loss of structures) that are hard to explain if algae only lived in water. For example, some green algae have lost their flagella, whip-like organelles that help single-celled organisms move around in water. All of the algae that are close relatives to land plants no longer have an eyespot, which they would use to swim toward light.-"Cell wall traits combined with the recently sequenced genome of terrestrial green algae Klebsormidium, (published in 2014, doi:10.1038/ncomms4978), revealed that this green alga shares a number of genes with land plants related to light tolerance and drought tolerance. With the genetic evidence in hand, we know that the traits have arisen linearly, rather than by convergent evolution.-"If their theory withstands scrutiny, it would begin to upend what's been cited in textbooks for over a century. The idea that plants jumped from water to land is credited to botanist Frederick Orpen Bower, although it is unclear whether that was his intended argument. In his 1908 tome "The Origin of a Land Flora," he simply proposed that the "invention" of alternating life cycles provided early land plants with a platform--the sporophyte--for evolutionary experimentation and thus adaptability.-***-"The researchers' biggest challenge will be to prove that a period of pre-adaptation led to the complex cell walls of land plants (although about 250 new genes were required for the formation of this terrestrial-friendly cell covering, which helps their case). They believe that these terrestrial green algae were advanced enough to survive on sandy surfaces, living on rain as a source of humidity. But with a small fossil record to go on--only spores exist from this period of evolutionary history--they will need to rely heavily on genetics to make their argument."-Comment: It seems they show evidence that land algae have been around a long time, but the issue still is, if life began in the sea, how did the algae get up onto land?