I already had a short posting about pre-Cambrian evolution in light of Expanding Earth hypothesis. Because of the profound implications of the hypothesis I decided to represent the model as short postings in the hope that it might find the response that it certainly would deserve.
Expanding Earth hypothesis is by no means not new. It was proposed by (see this) and I learned about it from the video animations of (see this and this) demonstrating that the continents fit nicely to form a single continent covering entire Earth if the radius is one half of the recent radius. What TGD has to give is a new physics justification for Expanding Earth hypothesis: cosmic expansion is replaced with a sequence of fast expansion periods increasing the value of Planck constant and these transitions occur in all scales.
If Expanding Earth hypothesis is correct it forces to modify dramatically the view about pre-Cambrian period. The super-continent theory could be replaced by much simpler theory and it might be possible to give up the assumption about hypothetical super continents and super oceans. The view about glaciations (see this) must be modified dramatically. Concerning the evolution of life the natural hypothesis is that it escaped to the underground seas formed as a consequence of expansion during pre-Cambrian era and returned back to the surface in Cambrian Explosion.
I have divided the discussion in short postings: 5 altogether. In the first posting I will discuss the notions of super-continents, super-oceans, and glaciations during Neoproterozoic period with short coments inspired by R/2 scenario. Next posting will discuss the dominating Snowball model for the climate during Neoproterozoic period in the same spirit. Third posting discussed TGD Expanding Earth view about super-continents, super-oceans and glaciations and compares it with Snowball Earth scenario. Fourth posting discusses paleomagnetic tests for R/2 scenario. Fifth posting discusses the Expanding Earth scenario about how life escaped to the underground lakes and seas created during the expansion and returned back in the beginning of Cambrian era.
Super-continents, super-oceans, and glaciations during Neoproterozoic period
1. Super-continent theory
Super-continent theory assumes a cyclic formation of hypothetical super continents (see this). Rodinia (see this), Pannotia (see this), and Pangea (see this) might have preceded by earlier super-continents. The period would be roughly 250 Myr.
- The super-continent Rodinia (see this) is assumed to have existed during interval: 1100-750 Myr. 750 Myr ago Rodinia rifted into three continents: Proto-Laurasia which broke up and eventually reformed to form Laurasia (North America and Asia), the continental craton of Congo (part of Africa), and Gondwana (now southern hemisphere plus India).
- Pannotia (see this) existed during time interval 600-540 Myr. Pannotia rifted in the beginning of Cambrian era to Laurentia (North America), Baltica, Siberia and Gondwana (see the illustration of Pannotia).
- Wegener (see this) ended up to postulate that super-continent Pangea should have existed about 250 Myr ago (see this). The support for its existence is rather strong since tectonic plate model and paleo-magnetic methods allows to trace the drift of the tectonic plates.
One can criticize the cyclic model. The concentration of land mass to Southern Hemisphere during Rodinia period does not look very probable event. The cyclically occurring formation of connected land mass surrounded by much larger ocean looks even less probable unless one can develop some very good physical mechanism forcing this. The basic motivation for super-continent theory are various correlations between distant parts of Earth which would cannot be understood otherwise. In R/2 model the the continents would have been quite near to each other during the expansion and the notion of cyclic formation of super-continents becomes un-necessary since land bridges between the continents could explain the correlations. There would have been just single super-continent all the time.
2. Standard view about oceans
In the standard model the total area covered by oceans has reduced since pre-Cambrian era due to the increase of the continental cover, which is nowadays 29 per cent. Oceans cover the remaining 71 per cent with Antarctica and Arctica included. The evolution of Oceans in standard model requires the introduction of hypothetical oceans which left no trace about their existence (subduction mechanism provides perhaps too convenient trash bin for hypothetical theoretical constructs).
- Proto-Atlantic Ocean was introduced to explain some contradictions with Wegener's Pangea model allowing to conclude which parts at opposite sides of Atlantic Ocean had been in contact. Proto-Atlantic Ocean closed as Pangea formed and opened again in slightly different manner to form Atlantic Ocean. This process implied mixing of older pieces of the continents and explained the contradictions. Large inland sea is a natural counterpart of the Proto-Atlantic Ocean in R/2 option.
- Mirovia (see this) was the super-ocean surrounding Rodinia. It transformed to Pan-African Ocean surrounding Pannotia. Pan-African ocean was then closed so that the ocean floor of Mirovia disappeared by subduction and left no signs about its existence.
- In the rifting (see this) of Pannotia Panthalassic ocean (see this) emerged and was the predecessor of the Pacific ocean.
The presence of super-oceans is forced by the assumption that the radius of Earth was the recent one during the pre-Cambrian era plus the local data related to the evolution of continents. The questionable aspect is that these oceans did not leave any direct trace about their existence. In R/2 model there is no need for these super-oceans except possibly the counterpart of Panthalassic Ocean (see this).
3. Glaciations during Neoproterozoic period
Glaciations dominated the Neoproterozoic period (see this) between 1-.542 billion years. The period is divided into Tonian (see this), Cryogenian (see this), and Ediacaran periods (see this). The most severe glaciations occurred during Cryogenian period.
It is believed that during Cryogenian period (see this) two worldwide glaciations -Sturtian and Marinoan glaciations- took place. This involves extrapolation of continental drift model and plate tectonics theory. Also hypothesis about hypothetical super-continents is needed so that one must take these beliefs with some skepticism. In R/2 model the world wide glaciations are replaced with ordinary glaciations proceeding from poles.
- Sturtian glaciation occurred 750-700 Myr. The breakup of Rodinia is believed to have occurred at this time. One can wonder whether there is a correlation between these events. R/2 model suggest that the energy needed to compensate the reduction of gravitational energy in expansion could have caused the cooling.
- Marinoan (Varanger) glaciation ended around 635 Myr ago.
Deposits of glacial tillites (see this) at low latitudes serve as support for the claim that these glaciations were world wide. In R/2 model Equator corresponds to North pole in TGD framework where Rodinia covered entire Earth and the interpretation would as ordinary glaciations.
After the end of Marinoan glaciation followed Ediacaran period during 635-542 Myr (see this). The first multicellular fossils appeared at this time. Their relationship to Cambrian fossils is unclear. The standard interpretation for the small number of fossils in pre-Cambrian period is that hard shells needed for fossilization were not yet developed. The problem is that these shells should have developed almost instantaneously in Cambrian explosion.
For details see the new chapter Expanding Earth Model and Pre-Cambrian Evolution of Continents, Climate, and Life of "Genes and Memes".