After having studied the most well-known mass extinction, the mass extinction at the K/T limit, we will examine the four other more significant ones: the extinctions at the Ordovician/Silurian, late Devonian, Permian/Triassic and finish-Triassic limits. If the probabilistic model is relevant, it is probable that we will be able to find, in these four mass extinctions, the same figure case as in the mass extinction to the finish-Cretaceous. The environmental evolution had to induce the biological evolution, thanks to the food chain probabilistic influence and the calcium biomineralization factors. If it can be considered as such, the main probabilistic role, but nonexclusive, from calcium, in the acme will be highlighted together with the extinction of living organisms significant groups, as well from protists as from metazoa.

It is the most significant mass extinction of the phanerozoic era. More than 200 organisms families disappear whereas the four other extinctions relate to approximately a hundred families each one. It is estimated that 13 % of the animal classes, 17 % of the orders, 49 to 52 % of the families, 72 % of the genera, between 80 and 95 % of the species (90 % of the marine shapes with shells; 78 % of the reptiles families, 67 % of those of the Amphibia), could have disappeared (Raup 1979), (Devillers, Chaline 1989), (Erwin, Valentine, Sepkoski), (Erwin 1996). All the groups decimated or extinguished at the P/T limit knew an apogee before this limit: Fusulinids Foraminifera, Ammonoids (Goniatids), Brachiopods (Articulated Class, Orders of Strophomenida and Orthida - superfamilies Orthacea and Enteletacea), Crinoids, Bryozoa and solitary Corals.

We will examine the principal Invertebrates groups reached or decimated at the P/T limit, with the approximate percentage of the extinctions of the families (Newell 1977)

Echinodermata

1) Crinoids: calcite exoskeleton representing between 95 and 99 % of the animal volume; the genera major part disappear at the Permian end, approximately 100 % (Roux 1988).

2) Cystoids: polygonal chalky plates formed tests, disappear at the Permian end, 100 %.

3) Blastoids: coronal chalky plates, extinct with Permian, 100 %.

4) Echinids: chalky tests ; the only genus which survives Triassic is Miocidaris which has only two interambulacral plates columns, whereas all the other Permian genera which disappear in have up to 8 (Erwin 1996), more than 50 %.

5) Ammonoids:Goniatites; chalky shells , acme with Carboniferous, die out with Permian, 100 %.

6) Trilobites: exoskeleton rich in calcium phosphate, benthic existence, nourishes mud and micro-plankton, progressive extinction since Ordovician, final with Permian, 100 %.

7) Ostracods: calcareous bivalvular carapace, more than 50 % decimated with terminal Permian

8) Brachiopods: calcium phosphate and/or carbonate cockle, frequently associated with Spongiae and Corallia, approximately 75 % of extinction (Strophomenida and Orthida - Orthacea, Enteletacea -) (Babin 1991).

9) Bryozoa: colonial organisms with calcareous or phosphated zoecies, especially met in the limestone facies, approximately 75 % of extinction (Trepostomes and Cryptostomes) (Theobald, Gama 1969).

10) Solitary corals: calcareous skeleton , the corallia represent the third of the limestones built on the surface of the globe, 100 % of extinction.

11) Fusulinids Foraminifera: bulky and heavy calcareous cockle (imperforated walls, basal cords), in limestones with fusulines, tests in great quantity associated with calcareous Algae , Polyps and Bryozoa, 100 % of extinction (Theobald, Gama 1969).

One can note that at the P/T limit, in these 11 marine invertebrates groups, with calcium carbonate or phosphate exoskeleton, the families are either extinct, or decimated from 50 % to 75 %. These groups of organisms calcic metabolism is more or less significant: Crinoids almost extinct with calcite skeleton between 95 and 99 % of the animal volume; Miocadaris, of small size, with mean test and two interambulacral plates columns, the only Echinidea genus which escapes the extinction whereas the other extinct genera have many interambulacral limestone plates columns; calcite tests or skeletons, aragonite, calcium phosphate, coronal calcareous plates , etc... Gastropods and the Bivalvia are also seriously reached (Pamela J.W. Gore 1997). Spongiae, which can have calcareous or siliceous spicules, appear relatively little touched.

Thus, 13 groups out of 14, with significant calcic metabolism, die out or are seriously decimated, that is to say 93 %. Such a high percentage cannot be alloted randomly.

If we analyze the Vertebrates case, it confirms the essential role of the calcic metabolism in the expansion and extinction of the families.

The Reptiles group dominates the terrestrial Vertebrates at Permian. Cotylosauria, the oldest Reptiles, have, in the unit, of the heavy, lumpish and relatively large forms: Limnocelis (2 m of size), Diadectes (1m, 50 of size), Pareiasaurus (3 m of size). Pelycosauria are only Permian forms: Dimetrodon, kind of enormous 3 m length chameleon with a dorsal peak supported by thorny apophyses a strange length (Theobald, Gama 1969). Eosuchia, groups living with the Primary and the Secondary borders, are generally of small sizes, but with many teeth. Mesosauria, are marine Reptiles and perhaps terrestrial, large-sized, with a long tail and many teeth. In these various forms, the calcic metabolism seems to play a major role. 78 % of the Reptiles families disappear at the P/T limit (Erwin 1996). The Amphibia class knows an expansion phase to the Permian-Carboniferous one. Among Permian Stegocephalia, existed large-sized forms, exceeding those of the current crocodiles, beside smaller forms ((Seymouria); Rachitomes: Edops (squat bones, cranium of 63 cm), Eryops (massive and well ossified members, cranium of 2 m) (Babin 1991), (Pamela J.W. Gore 1997), Actinodon, etc... Their body was covered with scales or dermic plates. Powerful bones closed completely the dome of the skull (Grasse 1992). As in the Permian Reptiles, the calcic metabolism role seems to have been dominating. One estimates the Amphibia families extinction percentage at the P/T limit to 67 (Erwin 1996).

With Permian, the super-continent Pangea formation involves the continents collision and the mountains erection (the Appalachian Mountains, Alleghany). Whereas calcareous sedimentation, during the Paleozoic one, had been abundant and in particular since Dinantian, the terminal Permian sees occurring the hercynian orogenese palatine phase and a sedimentation which had with the new mountain masses erosion, in mainly siliceous matter (variegated sandstone or Bundsandstein), on most of the sphere. At the same time an intense volcanicity involving considerable basaltic castings occurs (Siberia trapps rejecting into the atmosphere and the stratosphere from 2 to 3 million volcanic material Km3 rich in silica). South China knows, at the same time, significant volcanic eruptions (Erwin 1996) (Renne 1995). Volcanicity is accompanied by glaciations in the North and South Poles, by climate cooling and local dysaerobic facies in the not very deep oceans and by oxygen level fall (S.E. Sichuan, China - Wignall and Hallam 1998). Evaporites broad accumulations and hypersalines water are also observed (Pamela J.W. Gore 1997). CO2 released in the volcanic eruptions increases in the atmosphere and the oceans (Dewey Mr. McLean 1997).

Thus, at the Permian end, many calcium biomineralization disturbing probabilistic parameters were present, either on all the sphere surface, or on a regional level:

Factor 2: The glaciations with the two poles cool the temperature and not very deep oceans water

Factor 3: Higher consecutive CO2 level to the Siberia trapps and South China intense volcanicity in the atmosphere and the oceans (Renne 1995 - Erwin 1996)

Factor 4: Terrigenous erosion and dust rich in volcanic eruptions silica

Factor 5: Oceans hypersalinity attested by the evaporites accumulation (Pamela J.W. Gore 1997)

Factor 6: Anoxia in the oceans (Wignall and Twitchett)

Factor 7: Food chain breakage: fusulinids Foraminifera, Corals, Bryozoa, Brachiopods, etc...disappearance

It is noted that at the Permian end, the near total of the disturbing probabilistic biomineralization factors are in action, which explains with relevance the major mass extinction which occurs at the P/T limit.

The probabilistic model is in phase with the two extinction pulsations assumption at the Permian end, one in Guadaloupean, the other in Tatarian (Stanley and Xiangning Yang 1994).

They are roughly equal in intensity as we pointed out higher, of a hundred families order each one (Sepkoski 1986). The groups which disappear or which are most touched are always, Vertebrates or Invertebrates, protists or metazoa, significant calcium " consumers " for their internal or external skeleton construction. Briefly let us examine these 3 extinctions.

Among the hundred families which disappeared, the most concerned groups were Bryozoa, Brachiopods, solitary Corals, Trilobites, Graptolites, Echinoidea and Crinoids (Newell 1977) (Stanley 1991). All these organisms had a more or less significant calcic metabolism. Only Graptolites, seriously affected also, did not possess calcium made up skeletons. These organisms, planktonic for the majority, nourishing bacteria and other marine microscopic organisms were gathered in collagen protein tubes networks made similar to those of Pterobranchii (Ruppert and Barnes 1994). The Ordovician end is at the orogenetic caledonian cycle taconic phase. The continents were, at that time, biological deserts, vegetable cover for lack (the first air plants appear at this time). The continents were the erosion prey from where a terrigenous facies prevalence in the inferior Paleozoic seas (Auboin, Brousse, Lehman 1985). The caledonian chain installation was accompanied by metamorphism and granitisation. One passes from final Ordovician limestones to the lower Lhandoverian sandstones and schists. The terrigenous erosion importance is manifest. At the same time, the plate tectonics was responsible for a volcanic arc in North America. The climate cooled with a significant glaciation in Gondwana at the Ordovician end (Sahara drifts - Pamela J.W. Gore 1996).

Let us summarize the calcium biomineralization disturbing probabilistic factors at the Ordovician end

Factor 2: Paleoclimate cooling and Gondwana glaciation

Factor 3: Higher CO2 level in the atmosphere and the oceans due to the cooling and the CO2 discharge by the volcanoes

Factor 4: Terrigenous sedimentation by the erosion importance

As at the Ordovician and Triassic end, a hundred families disappear at the Frasnian and Famennian limit. The most concerned groups are, as in most of the extinctions, those of the marine community whereas the terrestrial flora and fauna are really concerned. The most affected taxa are the species of hot and tropical water and, in particular, the principal manufacturers of reefs: stromatoporoids, rough and tabulate corals. The other organisms which are seriously concerned are the floating Algae, Trilobites, Brachiopods, Conodonts and Acritarchs, primitive fishes and Ammonoids (Clymenids).

All these groups use, more or less, calcium for their exoskeleton or endoskeleton construction. Whereas the sponges with limestone spicules collapse, the sponges with siliceous spicules thrived and diversified at the Devonian end (Stanley 1991). At Agnathes, whereas Ostracodermi, " armoured Lampreys " with the dermic osseous formation more or less significant, by ossified shields (Osteostraci), plates (Anaspids) or osseous carapaces (Heterostraci) disappear, the Lampreys, with the cartiligeous body, persist. At Gnathostoma, Placoderms, fishes with cartiligeous internal skeleton have an osseous armour (Antiarchs and Arthrodiran). They die out almost completely in final Devonian whereas Acanthodii, with intern skeleton also cartiligeous, which carried only one spine in each fin front and were stripped of osseous armours as Placoderms persist until Permian (Babin 1991) (Theobald, Gama 1969).

The existence of the reefs, carbonates and evaporites in Devonian suggests a hot climate. In middle and final Devonian, a considerable change in the climate occurs with a glaciation in Gondwana (highlighted by the drifts in the Brazil North), a total cooling with vast black schist deposits and a marine biotic crisis which eliminates 70 to 80 % from the existing species with a narrow temporal correlation between these two events. Acadian orogeny in North America and caledonian in Great Britain and Norway generates the mountains erection and an intense erosion which produces the Old Red Sandstones powerful detrital series. One passes, to Europe, of frasnian limestones to the famennian schists (Auboin, Brousse, Lehman 1985). Correlatively, the volcanic eruptions develop along the earth's crust mobile belts which result from crumplings and the mountains erection consecutive to the rock plates gigantic collisions on the earth surface.

We find three calcium biomineralization disturbing probabilistic factors in final Devonian:

Factor 2: Gondwana glaciation and marine water total cooling

Factor 3: Higher CO2 level in the atmosphere and the oceans due to the cooling and the CO2 discharge by the volcanoes

Factor 4: Intense erosion and black schists vast deposits and the Old Red Sandstones detrital series

The groups which are mainly concerned were the Brachiopods, Ammonoids (Ceratites), the bivalvular Molluscs (Taxodonts), Gastropods and Conodonts (Theobald, Gama 1969), (Babin 1991). The labyrinthodont Amphibia and the marine Reptiles, except for Ichthyosauria which appear about this time, are decimated. All these organisms have a endoskeleton or a exoskeleton and a more or less significant metabolism.

During Triassic, where the continents are assembled in Pangea, the climate is generally hot and dry and the evaporites deposits accumulate. With the Triassic end, Pangea starts to be dislocated and the local volcanoes appear. Finish-Triassic corresponds to the alpine cycle cimmerian phase, especially significant in South-east Asia. One passes, at the Triassic end, from carnian and norian dolomites and the Keuper marls to Rhetian powerful basaltic flows (Auboin, Brousse, Lehman 1985). No glaciation and cooling seemed to have appeared with Triassic.

Factor 4: Orogeny, local volcanicity and the basaltic flow of Rhetian support terrigenous sedimentation

Factor 5: Transgressive water hypersalinity covering the evaporites episodically.

It is noted that, in these five mass extinctions, the organisms with composed calcium exoskeleton or endoskeleton, with more or less significant metabolism, undergo the effects of the appearance of the calcium biomineralization disturbing probabilistic factors.

Thus, in Ordovician, the organisms undergo the 3 calcium biomineralization disturbing probabilistic factors effects, in Devonian of 3 factors, Permian of 6 factors, the Cretaceous of 5 factors and with Triassic of 2 factors. These mass extinctions are preceded, generally, of radiations induced by the presence of calcium biomineralization probabilistic favorable factors: Ordovician, Silurian, basal and middle Devonian, Carboniferous and Permian, Mesozoic (Erwin, Valentine, Sepkowski).

1) At the K/T limit, the correlation between the persistence, the disappearance or the weak survival of 90 % of the genera at the K/T limit and their exoskeleton or endoskeleton composition; the one which exists, in space and time, between the Dinosaurs fossils local appearance and a preliminary transgression, i.e. a marine sedimentation which makes it possible to found the probabilistic trophic calcium chain; the calcareous sedimentation stratigraphic evidences change in siliceous sedimentation at the Cretaceous end, etc...

2) At the P/T limit, where 49 to 52 % of the families disappear; 13 invertebrates groups on 14, with calcium exoskeleton and calcic metabolism, die out or are seriously decimated, that is to say 93 %. In the same way disappear 78 % from the Reptiles families and 67 % of those of the Amphibia with significant calcic metabolism.

3) After ordovician radiation, at the Ordovician/Silurian limit, the most concerned groups are Bryozoa, Brachiopods, solitary Corals, Trilobites, Graptolites, Echinoidea and Crinoids; all these organisms, except Graptolites, comprise a calcium exoskeleton and a relatively significant calcic metabolism.

4) In late Devonian, the spongiae with siliceous spicules thrive at the limestone spicules spongiae expense; primitive fishes disappear (Ostracodermi and Placoderms, " armoured fishes ", with osseous plates and armours), whereas fishes which are not armoured (Acanthodii) persist.

5) With Finish-Triassic, the groups which are mainly concerned are always organisms with calcium exoskeleton and more or less significant calcic metabolism (Brachiopods, Ammonoids, bivalvular Mollucs, Gastropods and Conodonts).

The main arguments which validate the probabilistic model, in the mass extinction at the K/T limit, apply, in a similar way, with the other mass extinctions: " geological " duration, selectivity, animal groups former acme, prosperity and disappearance common denominator " simultaneous " of distant sub-kingdoms, Vertebrates and Invertebrates, trophic calcium chain, sedimentation character change during the extinctions, which passes from calcic dominant to siliceous dominant (by the orogenetic movements, volcanicity, magmatic intrusions). The other environment probabilistic factors disturbers of the calcium biomineralization are, by descending order: the glaciations and climate coolings (with Ordovician, with Devonian, with Permian and with Cretaceous), the CO2 increase in the atmosphere and the oceans (with Ordovician, with Devonian, with Permian and with Cretaceous), the oceans hypersalinity (with Permian, with Cretaceous and with Triassic), the food chain breakage (with Permian and with Cretaceous) and the anoxia (with Permian). These disturbing factors can have a regional or total action.

An analysis of the organisms which are mostly affected by several mass extinctions consolidates the probabilistic model. In the following enumeration the groups of which 50 % or more species were decimated during the various extinctions appear:

1 Spongiae (Devonian: siliceous sponges prosperity at the limestone sponges expense)

2 Cnidaria (Ordovician: solitary corals; late Devonian: tabulate corals, stromatoporoids; Permian: solitary corals, rough and tabulate; Cretaceous: corals)

3 Bryozoa (Ordovician; Permian: Trepostomes and Cryptostomes)

4 Brachiopods (Ordovician; Devonian; Permian; Triassic)

5 Molluscs (Devonian: Ammonoids, Clymenids; Permian: Ammonoids, Goniatids; Gastropods, Bivalvia; Triassic: Ammonoids, Ceratites; Bivalvia, Taxodonts; Gastropods; Cretaceous: Ammonoids; Belemnoids; Nautiloids; Oysters, Hippuritids; Pelecypoda)

6 Arthropoda (Ordovician: Trilobites; Devonian: Trilobites; Permian: Trilobites; Ostracods)

8 Vertebrates (Devonian: Primitive Fishes, Ostracodermi, Placoderms; Permian: Amphibia, Reptiles, Pelycosauria; Triassic: labyrinthodont Amphibia; marine Reptiles except Ichthyosauria; Cretaceous: Osteichthyes fishes; terrestrial and marine Reptiles)

9 Graptolites (Ordovician)

10 Conodonts (Devonian, Triassic)

Among Protists, Coccolithophoridae, appeared in Carnian (higher Triassic), are decimated at the K/T limit. As for Foraminifera, they are almost extinct with Permian (fusulinids) then with the Cretaceous (Globigerines, Orbitoids). All these groups decimated, often on several occasions, protists or multicellular organisms (except for the graptolites which nourishes bacteria and planktonic microscopic organisms), have an exoskeleton or endoskeleton of compounds of calcium and a more or less significant calcic metabolism.

A last strong argument of the influence of the trophic calcium chain and calcium biomineralization probabilistic factors on the organisms acme and their mass disappearance is history of the tropical reefs. These reefs testify to the limestone importance in their construction, aragonite, calcite, carbonates, etc... According to times, the recifal formations were worked out by very diverse organisms, solitary or colonial Corals, symbiotic limestone Algae, Spongiae, Tabulata, Tetracorallia, Hexacorallia, Madreporia, etc... and even of Lamellibranchiata (Cretaceous Rudists). Calcium plays a fundamental role in the recifal constructions which represent a limestones third built on the sphere surface. The coral reefs are accompanied besides by perirecifal formations (oolitic limestones, lithographic limestones, etc...) (Theobald, Gama 1969).

If one shares the history of the tropical reefs in three periods (Copper 1988): 1) the periods of the beginning of the development 2) the periods of full development 3) the periods of complete absence, one notes:

Periods 1 and 2 of beginning and/or full development coincide with the radiation periods which precede mass extinctions: basal and middle Cambrian, Ordovician, Silurian and basal and middle Devonian, Carboniferous and Permian, Triassic, Jurassic and Cretaceous, Tertiary, i.e. the periods when calcareous sedimentation and the probabilistic factors favorable to the calcium biomineralization prevail.

Periods 3 of the total absence of the tropical reefs coincide exactly with the times of the 5 most significant mass extinctions: limit Ordovician/Silurian, late Devonian, limit P/T, finish-Triassic, limit K/T (more final Cambrian), i.e. the periods when siliceous sedimentation is essential (orogeny, volcanicity, etc...) and where the calcium biomineralization disturbing probabilistic factors decimate the organisms which produce the tropical reefs.

The correlation between the tropical reefs acme and disappearance and the establishment of the favorable or not to the calcium biomineralization probabilistic factors is not to be denied.

Annelids, which exist since the Precambrian one, very little provided in calcium exoskeleton (apart from some Polychaeta, Serpule, Pomateceros with calcareous tube, Spirorbis of Silurian, etc...) suffer generally little from the mass extinctions.

Among the Vertebrates ones, let us recall fishes little or not affected: Chondrichthya: Elasmobranchii with cartilage exoskeleton (67 % of survival to the Cretaceous) whereas Osteichthya, fishes with calcium exoskeleton are decimated (4 % of survival to the Cretaceous). Also let us recall the siliceous spongiae prosperity to the Permian end whereas the calcareous spongiae collapse.

In short, the impressive facts mass that we have just quoted largely make credible the probabilistic interaction model validity between a environment parameter, the calcium, and the organisms, as well invertebrates as vertebrates, protists or metazoa.