[MUSIC] We will now move forward to the Neoproterozoic era that started about a thousand million years ago. Organic microfossils from the Neoproterozoic are not unusual. But it was shown in 2010, by an American research team, that the highest diversity occurred between 800 million and 700 million years and again somewhere after 580 million years. Also, the morphological disparity among microscopic eukaryotes, which may be explained as morphological variation, increased during the Neoproterozoic. The rising acritarch diversification in the early Neoproterozoic has been related to the evolution of sexual reproduction in the late Mesoprotozoic, and the British research group led by Timothy Lenton showed in 2014 that the so-called cyanobacteria-dominated biological pump in the oceans was replaced by the eukaryote-dominated pump starting before the Cryogenian glaciations. Some of the important Eukaryotes that evolved just before the glaciations include testate amoebae, and very small 10 to 30 microns phosphatic, eukaryrotic scales preserved in about 800 million years old rocks from Canada. It is not certain what has driven this pre-glacial Neoproterozoic diversification among the eukaryotes. But it was suggested by Susanna Porter in 2011 that predation among uni-cellular organisms may have had an influence on the rising diversity. It is possible that also the oceanic increase in oxygen and nitrogen have had an effect. The Cryogenian Period spans an interval from 850 to 635 million years. It includes two major glaciations called the Sturtian and Marinoan glaciations and a smaller named the Gaskiers glaciation. This Cryogenian glacial event is sometimes called the Second Snowball Earth not to be confused with the Paleoproterozoic Snowball Earth event. The name Snowball Earth is related to the hypothesis that the cold period resulted in very extensive glaciations. Perhaps causing that the ocean bottom at times was frozen solid even at low latitudes. Some scientists are sceptical to this and suggest that it only reached a so-called "slush-ball" stage. No matter what is true, it is clear that the glacial period influenced negatively on the evolution and diversification of life, as it has been shown that the diversification of eukaryotes was significantly lowered during the glacial events. The Rodinia Supercontinent did form some 900 million years ago and broke up again at about 750 million years. The Cryogenian glaciations occurred just after the break up, between 720 and 580 million years. An international research team published in 2009 in Nature the oldest evidence of Metazoa. More precisely they detected biomarkers indicating the occurrence of the group of sponges called Demospongia from 635 million years old rocks from the end of the Cryogenian. The living natural bath-sponges, which some of you may know to also belong to the Demospongia. Demospongia are benthic organisms living on the sea floor both in marine environments and lakes. An intriguing hypothesis was published by Lenton and co-workers in 2014 in Nature Geoscience. They suggested that both the shift from cyanobacteria to eukaryotic algae as primary oxygen producers and the appearance of filter-feeding benthic animals like the sponges, had a significant influence on both ventilation of the shelf seas and the removal of phosphorous. As a consequence, they hypothesized that the amount of phosphate and global oxygen demand in the sea, decreased during the Neoproterozoic without requiring an increase in the atmospheric oxygen. The result was more oxygenated sea-water and diversification of higher- oxygen-demanding animals. After a long and relatively stable period that lasted from the mid-Mesoprotozoic, to approximately 600 million years, atmospheric oxygen levels began to rise again, especially in the late Neoproterozoic, just after the end of the glacial period. Analysis of the iron content of deep-sea sediments from Newfoundland, shows that the deep ocean was anoxic and ferruginous, that is rich in iron-2, before and during the last of the Neoproterozoic glaciations around 580 million years ago that is called the Gaskiers glaciation. Don Canfield and co-workers have shown, however, that the oxygen content of the deep sea rose significantly just after the last Neoproterozoic glacial period. The first convincing Metazoan fossils were found in the Ediacarian, nearly 575 million years ago in old phosphoritic sediments from the Yangtze platform, southeast China. This very unique Lagerstatte has been named the Doushantuo Formation Lagerstatte. The exceptional fossils include both putative metazoan embryos, larvae, and microfossils; unnamed, mature, possible Cnidaria which possibly are Hydrozoans and tubular fossils that probably belong to Cnidaria, which is the phylum where also corals belong. The Doushantuo biota was succeeded by the Ediacara biota, consisting of several different macroscopic and microscopic ecosystems recognized globally. The Ediacara biota consists of very special organisms representing puzzling tubular and frond shaped, mostly sessile organisms, which lived during the Ediacaran period from 635 million years ago to 541 million years ago. The Ediacara biota radiated about 575 millions years ago, just after the end of the Cryogenian period's extensive glaciations. The biota didn't survive the Precambrian/Cambrian boundary at 541 million years. The taxonomical classification of most of the organisms is currently unsolved. Fossil of both sponges, that is Porifera, and more advanced animals called Bilateria have been found from the period just before the Cambrian, but the Ediacaran period was mainly characterized by experimental life forms without secure ties to the living organism groups, and they had only a very short temporal extent, geologically speaking. It was suggested by Buss and Seilacher of Yale University that several taxa were so special that they were transferred to a new kingdom called Vendobionta. Originally, in 1994, Seilacher interpreted them as a possible sister group of the Eumetazoa, but nine years later, he and co-workers suggested the quite controversial idea that they may instead be giant protozoans. Perhaps related to Foraminifera. But perhaps we are now a little bit closer to understand these extraordinary fossils. In 2014, Danish scientists from the Natural History Museum of Denmark discovered and described a new living non-bilaterian genus, called Dendrogramma originating from between 400 and 1,000 meters depth offshore Tasmania. It has been suggested that Dendrogramma perhaps may be related to representatives of the Ediacara biota. At the entrance to the Cambrian the development of life began to take a serious hold among multi-cellular organisms, particularly among the metazoans. Many new features were invented such as hard skeletons and hard teeth. The oxygen content increased also in the deep part of the oceans, and organisms developed new feeding strategies and occupied new niches and habitats. The resulting explosive rise in biodiversity has been called the Cambrian explosion. [MUSIC]
