The sudden emergence of advanced multicellular lifeforms in the Cambrian Explosion (CE) about 540 Ma ago is still one of the great mysteries of mainstream biology. The team led by ETH researcher Andrea Giuliani found in rocks from deep mantle what can be regarded as traces of CE. The proposal is that partly organic material would have been subducted to the deep mantle after CE and changed the isotopic compositions of Carbon and other elements. Also other elements, for instance strontium and hafnium showed a pattern similar to carbon.
The group of Giuliani examined rare diamond-containing volcanic rocks known as kimberlites from different epochs of the Earth's history. These special rocks originate from the lowest regions of the Earth's mantle. The isotopic composition of carbon in about 150 samples of these special rocks was determined. The composition of younger kimberlites, which are less than 250 million years old, was found to vary considerably from that of older rocks. In many of the younger samples, the composition of the carbon isotopes is outside the range that would be expected for typical rocks from the mantle.
The isotope ratio R=13C/12C for Carbon in the deep mantle is considerably lower for the kimberlites younger than 250 Ma whereas the value for kimberlites older than 250 Ma is typical mantle value. The values of younger kimberlites are also more variable. More quantitatively, δ(13C)= (Rsample/Rstandard -1)× 103 serves as a parameter. For a typical sample from the mantle, the value is δ ≈ -5+/- 1 per mille whereas for the studied samples δ is in the range [-20.-30] per mille.
The increased subduction caused by plate tectonics of the material from the surface of Earth could explain this. The estimate is that it takes 200 Ma for the material from the surface to reach the lower mantle. In the standard geology, the natural interpretation is that the dramatic increase in the generation of organic matter in CE has reduced the carbon isotope ratio. One must however assume that the partly organic material from the surface should have ended down to the deep mantle along specific routes by subduction.
Is the TGD inspired hypothesis for Cambrian Explosion life consistent with these findings?
- The proposal is that life evolved in underground oceans ("womb of Mother Gaia'') and suddenly emerged to the surface in the CE as highly developed multicellular organisms. CE was caused by a rapid increase of Earth radius by factor 2, which generated bursts of the underground water reservoirs to the surface and created the oceans. The expansion broke the Earth's crust to pieces and led to the emergence of plate tectonics, subduction, and oceans. Note that in Mars this tectonics is not present and the radius of Mars is actually roughly 1/2 of the radius of Earth.
- The rapid increase of the Earth radius is the TGD counterpart for a smooth increase of Earth radius in cosmic expansion. All astrophysical objects look as if they would not participate in cosmic expansion: this is a mystery in general relativity. In TGD this mystery is resolved by replacing smooth cosmological expansion with a sequence of rapid expansions followed by stationary periods (see this and this.
- The conclusion of Giuliani et al seems undeniable: the isotope decomposition in the mantle changed 200 Ma ago and was caused by the transport of the material affected by CE to the lower mantle.
- In the TGD framework these findings do not however force the conclusion that life emerged suddenly in CE. Rather, multicellular life was present in the underground oceans before CE but plate tectonics and subduction were absent.
The increase of the radius of Earth reduced the average density of Earth dramatically, and created the proposed subduction routes to the lower mantle, which dramatically increased the rate of transport of the organic material to the deep mantle.
- >Interestingly, the process analogous to CE appears to have occurred episodically throughout most of Earth’s history, with the oldest diamonds that contain eclogitic inclusions forming at roughly 3 billion years (Ga) (see this). In the TGD framework this suggests that the rapid expansions of Earth have occurred episodically and have led to the emergence of life forms from the interior to the surface and the transport of the material containing organic carbon to the mantle.
For a summary of earlier postings see Latest progress in TGD.