The Tonian Period

The Tonian period marked the beginning of the Neoproterozoic; this period is roughly estimated to be started when the Grenville orogeny was at its end, which was nearly1.0 billion years ago, and this period lasted till 850 million years ago. The name for this period was said to have been taken from a Greek word that means stretching, this period witnessed numerous shifting and stretching of the continental plateaus and hence justifies its name quite appropriately. This drifting of the continental plates leads to the breaking up of Rodinia. Due to this continuous stretch and drifting of the tectonic plates, the crust of the stretched areas became thinner and lead to the formation of the inland seas. A lot of evidences proved this fact like the stromatolites covered drowned cartons which have been found at large.

The most interesting thing that is to be noticed about the Tonian era is the Acritarchs' first radiation, which means something whose origin is uncertain. These are organic microfossils which were mostly found in the sedimentary rocks that originated in the marine or the saline water areas and the very term refers how they were taken from the sediments. The sedimentary rock was initially pulverized and then was made to dissolve in hydrofluoric acid. These organisms did not dissolve in the acid solution showing that they were made of and skeletons, which were non-siliceous and non-carbonaceous. Thus, they were easily extracted out of the solution. They clearly revealed to have an organic walled structure that contained absolutely no mineral along with the remains of different organisms mostly in the stage of cyst.

We first come across the Acritarchs in the geological records that dated back to 1.4 billion years, at the starting time of the Ectasian. They were known to have revealed the inclusion of various organisms, which included the remains of the eggshells of tiny metazoans to various kinds of green algae or chlorophyta. It can be assumed that some species of the acritarch may even represent resting or cyst stages of algae which were the ancestors to the dinoflagellates. However, natures of the organisms which can be associated with the older acritarchs were not known though according to some geologist they are related to the marine algae, which were unicellular. Theoretically, when it is not possible to come to any conclusion regarding the biological origin or the taxon of the acritarchs, it is good to classify them with their respective group.

The Tonian period saw a great influx of the diversified species of the Acritarchs which profusely grew through the entire Neoproterozoic era and only during the Cryogenian glaciations they face a small decrease in their number.

During the Tonian period, Rodinia was the super continent. Mirovian Ocean is the only ocean which surrounded this super continent. There were numerous inland seas, most of which occurred during the Tonian period. The Stromatolites were found in the salty water as well as in the fresh water. They were also in abundant in places like the marine coastal line which had the marine environment.