After calcium and iodine, a third probabilistic interaction application between the environmental evolution and the biological evolution is proposed. It relates to the free molecular oxygen rate evolution in the Earth's atmosphere during ages, which can also be regarded as a stimulus to which the organisms, its origin and its consequences react.

In the present state of knowledge, the data on the atmospheric oxygen rate, during various geological periods, are full of uncertainties, discussed by the various authors and prone to permanent calling in question, with the researchers works thread. In what follows, we tried, nevertheless, to establish a probable middle increase chronology in the oxygen rate in the Earth's atmosphere. Because of the preceding reserves, one must regard this chronology various stages more as magnitude orders that like precise and rigorous datings (Holland 1984-1998; Mason 1992). It is not excluded, moreover, that the PO2 P.A.L. rate knew fluctuations during geological periods.

Crust/ocean/atmosphere system enrichment in free PO2 P.A.L. intervened, mainly, following photochemical reactions grouped under the photosynthesis generic term (Rybak 1974) and, marginally, of the water vapor photolysis. This process is, presently, primarily, the plants fact. One considers the free molecular oxygen present percentage at 5 % oxygen present total at the earth's crust surface (Schidlowski, Eichman 1977).

We indicate below the earth's atmosphere in PO2 P.A.L. enrichment principal stages since the earth origin (4,6 Billion Years) until today, of which we gave, to Chapter VI, the essential data. The figures indicated are based, either on geological arguments (various radioactive elements isotopic ratios, U 238, K 40, C 14, etc...), or on biological arguments (biological processes physiological thresholds: aerobiosis, collagen production, cutaneous respiration, etc...).

1) Hadean (4,6 to 3,9 B.Y.) the earth paramount atmosphere is made up mainly hydrogen, methane and ammonia (planetologic arguments). This time intense volcanic degazifications do not contain free molecular oxygen. PO2 P.A.L. = 0

2) Archean (3,9 to 2,5 B.Y.) uraninite deposits (UO2.) and pyrite (FeS2) until towards 2,3 B.Y. indicate atmosphere not-oxydative conditions with PO2 P.A.L. rates probably going from 0,0005 to 0,005 (Holland 1998). PO2 P.A.L. = > 0,0005

3) Proterozoic (2,5 to 0,544 B.Y.)

a) Between 2,8 and 1,8 B.Y., B.I.F. deposits (Banded Iron Formations - ribboned iron Formations) alternate layers rich and low in magnetite (FeO4) (Guntflint Chert 1,9 B.Y.), also indicating not-oxydative atmosphere.The photosystème II, appeared towards 2,7-2,5 B.Y. seems to have been dominating and to have caused the increase in the O2 molecules in the atmosphere. Abundance peaks between 2,5 and 2 B.Y., coinciding with the uraninites disappearance indicate an increase in the PO2 P.A.L. rate (Holland 1998). PO2 P.A.L. = > 0,005

b) The Red Beds (Red Formations) hematite (FeO3) deposits appear towards 2,00 B.Y., indicating oxydative atmosphere conditions and lead to the B.I.F. disappearance towards 1,8/1,7 B.Y. with the ozone layer O3 development (Levin). The increase in the molecules O2 in the atmosphere allows the emergence of the oldest known aerobic eucaryote cells, approximately 1,9 B.Y. old (Gryptania spiralis - Pan Terra 1996); 0,01 threshold for the protists aerobic breathing (Holland 1998). PO2 P.A.L. = > 0,01

c) Vendian (0,565 B.Y.) Between 0,750 and 0,550 B.Y., the carbon isotopic composition suggest an appreciable increase in the PO2 P.A.L. rate before the cambrian era (Hoffmann, Kaufman, Halverson 1998). The geochemical data clearly indicate a rise in the PO2 P.A.L. rate right before the Vendian macroscopic animals appearance. They also show a phytoplankton dynamic evolution at the Precambrian/Cambrian (Knoll 1996) border. In addition, the apparition of the ediacarian fauna of soft body metazoa requires, for the collagen, muscles production and the cutaneous respiration (Dickinsonia: 1 meter length for a maximum thickness of 6 mm), a 0,07 PO2 P.A.L. minimum (Towe 1970 - Bruce Runnegar 1982 - Rudolf, Elizabeth Raff). PO2 P.A.L. = > 0,07

4) Paleozoic (0,544 to 0,250 B.Y.)

a) Cambrian (0,544 to 0,505 B.Y.) "the cambrian explosion", with its various episodes, S.S.F. (Small Shelly Fossils), tommotian and atdabanian radiations, the Burgess Shale fauna, implies an increase in PO2 P.A.L. necessary to the organisms complexification and their biomineralization. The correlation between PO2 P.A.L. and the living organisms evolution is corroborated by many data compilation which we indicated in Chapter VI and which we point out here. The analysis of these data (Rhoads, Morse 1971) made it possible to show the relation between the dissolved oxygen level and the fauna benthic presence in the basins on low oxygen level, in the Black Sea (Bacescu 1963), the Gulf of California (Parker 1964), the Basin of Santa-Barbara (Emery, Hulsemann 1961) and the Basin of San Pedro (Hartman 1955, 1966). They established that faunas can be classified in three facies correlated at different PO2 P.A.L. rates. With a value < 0,1 ml/l (approximately 0,01 PO2 P.A.L.), the marine sediments are primarily metazoa benthic deprived; for a value ranging between 0,3 ml/l and 1 ml/l (between approximately 0,03 and 0,10 PO2 P.A.L.), benthic faunas are made up small species mainly with soft body; when the level is higher than 1 ml/l (approximately 0,10 PO2 P.A.L.), faunas are relatively varied and made up many species which secrete skeletons limestones. Similar relations were observed in the Saanich split in the Vancouver Island (Tunnicliffe 1981). Rhoads and Morse proposed that these relations between the faunas emergence and the oxygen rates dissolved in these basins are regarded as analogues with the metazoa groups development during the Proterozoic last stages and the Phanerozoic first stages. PO2 P.A.L. = > 0,10

b) Ordovician (0,505 to 0,438 B.Y.) The first appearance of terrestrial life would go up in middle Ordovician where terrestrial spores traces are found (0,449/0,458 M.A.- Jane Gray) but not from vascular plants.The first spores would be perhaps dated from Cambrian. The PCO2 P.A.L. level before 0,440 B.Y. would have been higher 16 to 18 times on its present level (Crayton J.Yapp 1998). PO2 P.A.L. = > 0,10

c) Silurian (0,438 to 0,408 B.Y.) If the possibility of plants and terrestrial animals is probable in Ordovician, their obviousness is established in Silurian with the plants vascular fossils (Cooksonia), perhaps of Lycophytes (Baragwanathia?), mushrooms (ascomycetes) and Arachnida and millipede first fossils (Taylor and Taylor 1993). The analysis, by stable isotopes geochemical methods, makes it possible to provide the oxygen lower level rate, during the last 440 million years. This rate would not be lower than 0,13 (Crayton J.Yapp 1998). PO2 P.A.L. > 0,13

d) Devonian (0,408 to 0,360 B.Y.) From upper Silurian to higher Devonian, one attends a considerable development of the vegetable cover by terrestrial vascular plants with the sheets, roots, secondary tissues and seeds acquisition. Concomitantly, the PCO2 P.A.L.. rate falls quickly and in a very significant way (Algeo and Scheckler 1998). An imbalance between the oxygen production by the carbon cycle and its consumption by the sulphur cycle, by only 5 %, can increase the PO2 P.A.L. rate of 50 % in 40 million years. The iron cycle can also intervene in this imbalance. On the long term, a balance is roughly established between the sulphur cycle and the carbon cycle which is an atmosphere/ocean/terrestrial crust system redox state major element (Holland 1984). During middle and higher Devonian, the increase in the vegetable biomass accelerates the atmospheric CO2 "pumping" level towards the ground and establishes a carbon cycle new long-run equilibrium, between its production and its consumption, which is maintained until our days (Algeo, Scheckler and Maynard 1998). It is estimated that the atmospheric PCO2 P.A.L. level between Silurian and higher Devonian is divided by 5 or 6 (Berner 1994). One can suppose, reciprocally, an increase in atmospheric PO2 P.A.L. of the same magnitude order. This assumption is corroborated by Heinzinger, Schidlowski and Junge work (1974). These authors, by comparing the isotope § 18 O value (11,4 o/oo SMOW), in meteorite magnetite spangles dating from higher Devonian, found values around 0,65 (11,4/17,6) of those of the recent samples § 18 O (17,6 o/oo SMOW). Other magnetite spherules, dating from Oligocene gave values appreciably equivalent to those of today (17,4 o/oo SMOW). The atmospheric isotope § 18 O respective values give, for superior Devonian 17,3 o/oo SMOW, for the Oligocene one, 23,3 o/oo SMOW and 23,5 o/oo SMOW for today is a value of 17,3/23,5 = 0,74 PO2 P.A.L. for Devonian. PO2 P.A.L. = 0,65 to 0,74

d) Carboniferous/Permian (0,360-0,250 B.Y.)

5) Mesozoic (0,250 to 0,065 B.Y.)

The carboniferous flora and the terrestrial vascular plants radiations during the Permian and the Triassic, with the PCO2 P.A.L. rate decrease (Berner 1994), could carry the PO2 P.A.L. oxygen rate which one estimates at 0,93 with the Gymnosperms blooming (Coniferals) until lower Cretaceous. PO2 P.A.L. = 0,93

6) Cenozoic (0,065 B.Y. - present)

Of the Cretaceous until our days, develop Angiospermae. A last increase in PO2 P.A.L. partial pressure had to occur during the Cretaceous various oceanic anoxic events OAEs (Holland 1984), carrying it to its present value with the Cenozoic one. PO2 P.A.L. = 1

As we indicated higher, crust/ocean/atmosphere system enrichment in free PO2 P.A.L. intervened, mainly, following photochemical reactions grouped under the photosynthesis generic term (Rybak 1974) and, marginally, of the water vapor photolysis. This process is, presently, primarily, the product of the plants (Knoll 2000).

This environment parameter, that the probabilistic model regards as a stimulus to which the organisms react is, as we will see it below, itself produced by the living organisms evolution during geological times, from the procaryotic photosynthetic unicellular organisms then eucaryotes and later plants.

The following table establishes the correlation observed between the producing oxygen organisms biological evolution and the increase in the atmosphere free molecular oxygen PO2 P.A.L. partial pressure. This table indicates: 1) the billion years age 2) producing oxygen present organisms 3) estimated PO2 P.A.L. rates.

4,6: no life, possible water vapor photolysis, null or negligible PO2 P.A.L. (Holland 1984). PO2 P.A.L. = 0.

3,85: Isua carbonated sediments (Mason 1992), life traces (carbon 12, Akilia island) (Mojzsis and Arrhenius 1996), null or negligible PO2 P.A.L.. PO2 P.A.L. = 0

3,5: life traces, stromatolites, archaes (?), autotrophic bacteria, oxygen not-producing, filamentous bacteria, Australia Warrawoona fossils (North Pole); null or negligible PO2 P.A.L. (Mason 1992). PO2 P.A.L. = 0

2,8: stromatolites, proalgae, blue algae cyanobacteria precursors, procaryotic, anaerobic photosynthesis (chemosynthesis) and aerobic with oxygen release (Schidlowski, Eichman 1977), (Schopf 1977), (Whitaker, Klein 1977), (Brack, Raulin 1991), (Holland 1998). PO2 P.A.L. = < 0,005

Proterozoic

2,5 to 2,3: B.I.F. (Banded Iron Formations) and uraninites, more than 58 listed spheroid microfossils genera (Boureau 1986), procaryotic aerobes, PO2 P.A.L. 0,005 to 0,01 (Holland 1984), (Mason 1992). PO2 P.A.L. = 0,005 to 0,01

2,0: B.I.F., Gunflint Chert ribboned iron formations, ozone layer, abundant aerobic procaryotic blue algae, 10 microns in diameter, similar to present Nostocs, PO2 P.A.L. from 0,01 to 0,02 (Schidlowski, Eichman 1977), (Margulis 1977), (Holland 1984), (Mason 1992). PO2 P.A.L. = 0,01 to 0,02

1,9 to 1,5: hematite red layers, first known aerobic eukaryote cells (Gryptania spiralis - Pan Terra 1996), cells increase, acritarchs (40 microns diameter), mitosis, meiosis, green and red algae. PO2 P.A.L. > 0,02 < 0,07

1,5 to 0,565: acritarchs radiation towards 0,900/0,850 then quasi-disappearance towards 0,600; first unicellular green eucaryote algae fossils equipped with distinct chloroplasts; first multicellular plants fossils with structures similar to salads and kelps (1,4-1,2 Butterfield 1998); increase in the eucaryote microflore and reduction in the procaryotic microflore, in particular because of the eucaryotes greatest capacity to use available phosphate (Lehman, Botkin, Likens 1975); increase in the photosynthesis and the free molecular oxygen rate (Cloud 1990) and in the organic carbon sedimentation (Knoll 2000), Algae era. PO2 P.A.L. = < 0,07

0,565 to 0,544: phytoplankton dynamic evolution which involves an increase in the atmospheric oxygen level right before the macroscopic Ediacara fauna appearance at the Precambrian end (Knoll 1996), (Heinrich D. Holland 1998). PO2 P.A.L. > 0,07 = < 0,10

Paleozoic

0,544 to 0,505: (Cambrian): possible terrestrial first spores (Brasier 1979), (Bengtson, Conway 1984); " Thallophyta era " (British Columbia, Conway Morris and Robinson 1988). PO2 P.A.L. = > 0,10

0,505 to 0,438 (Ordovician): first terrestrial plants spores fossil obviousnesses, terrestrial vascular Crytogams possibilities, Protopsylophytes in higher Ordovician (Auboin, Brousse, Lehman 1985), (Babin 1991). PO2 P.A.L. = > 0,10

0,438 to 0,408: (Silurian): terrestrial vascular plants and terrestrial photosynthetic production of O2 obviousness and development which supplants the primarily marine photosynthetic production former to Silurian (Holland 1984). In higher Silurian, first poikilotherms

(Cooksonia) and Lycopodophytes (Baragwanathia?), "Thallophyta era", photosynthesis on the continents (Theobald, Gama 1969), (Auboin, Brousse, Lehman 1985), (Babin 1991), (Crayton J.Yapp 1998). PO2 P.A.L. > 0,13

0,408 to 0,360: (Devonian): continental flora diversification, terrestrial vegetable cover considerable development, Pteridophyta explosion (Psilophytines - Rhynie flora -, Lycopodiophytines, Equisetophytines, Filicophytines, etc...); "vascular Cryptogams era" (Theobald, Gama 1969), (Auboin, Brousse, Lehman 1985), (Babin 1991), (Holland 1984). First Spermatophyta. First forests with high sizes trees (of 8 m up to 30 m). Vegetable diversification is regarded as a "devonian explosion" (R. Goldring 1978). It is estimated that the terrestrial ecosystems photosynthetic productivity exceeds that of the marine ecosystems of a factor 2 (Whittaker, Likens 1975; McLean 1978). Terrestrial vegetable photosynthesis acceleration with the PCO2 P.A.L. fast fall (Berner 1994) and PO2 P.A.L. significant growth (Heinzinger, Schidlowski, Junge, 1974). PO2 P.A.L. = 0,65 to 0,74

0,360 to 295: (Carboniferous), immense marshy forests, carboniferous flora supporting the coal formation, Pteridophyta considerable development, Pteridospermales and Cordaitales appearance.

0,295 to 0,250: (Permian) and 0,250 to 0,065 (Mesozoic) Phanerogams development, " Gymnosperms era " then of Angiospermae (starting from the lower Cretaceous - Ranunculus ferresi) (Theobald, Gama 1969), (Auboin, Brousse, Lehman 1985), (Babin 1991), (Holland 1984), (Heinzinger, Schidlowski, Junge, 1974). PO2 P.A.L. = 0,93

Cenozoic

0,065 to Present: (Tertiary - Quaternary): Angiospermae radiation (Monocotyledoneae and Dicotyledoneae). PO2 P.A.L. = 1

If one analyzes the earth's atmosphere enrichment, from Archaean to Cenozoic, one notes that this average atmosphere enrichment is concomitant with the successive appearance, in the biosphere, of increasingly powerful oxygen producing organisms, from the Archaean cyanophyta and the blue and green procaryotic algae to the pluricellular " higher " eucaryote organisms, like present Angiospermae. One can distinguish, in the PO2 P.A.L. rate evolution five significant phases or thresholds:

1st phase (2,8 to 2): cyanobacteria, procaryotic algae, monera. PO2 P.A.L. = < 0,01

2nd phase (2 to 0,565): monera, protists, acritarchs, first multicellular plants, Schizophyta and Thallophyta, " algae era ", primarily marine plants. PO2 P.A.L. = < 0,07

3rd phase (0,565 to 0,438): Thallophyta development, first terrestrial spores in Ordovician, first terrestrial vascular plants in higher Ordovician. PO2 P.A.L. > 0,13

4th phase (0,438 to 0,360): development in Silurian then " explosion " in Devonian of the Pteridophyta vegetable cover, " vascular Cryptogams era ", primarily terrestrial plants, with photosynthetic productivity double that of the sea plants (Whittaker, Likens 1975; Mc Lean 1978), PCO2 P.A.L. fast fall and concomitant increase in PO2 P.A.L. PO2 P.A.L. = 0,65 to 0,74

5th phase (0,360 - Present): terrestrial flora considerable development at Carboniferous and Permian, " Gymnosperms era " from Permian to the lower Cretaceous, " Angiospermae era " from the lower Cretaceous to Present with a PO2 P.A.L. rate = 1 at the Cenozoic PO2 P.A.L. = 1

This PO2 P.A.L. evolution, from Archaean to Present, is proposed like model, with uncertainties which are attached to it, in the entirely reliable and precise data absence. The most coherent values that one can retain, in the knowledge present state are: PO2 P.A.L.: 4,6 (Hadean) = 0; 2 (Proterozoic) = < 0,01; 0,565 (Vendian) = < 0,07; 0,438 (Silurian) > 0,13; 0,408 to 0,360 (Devonian) = 0,65 to 0,74; Present = 1. The preceding restrictions do not affect the process total interpretation.

The correlation between the producing oxygen organisms evolution, of the aerobic monera to the terrestrial plants, from Precambrian to Cenozoic, and the partial pressure of free molecular oxygen in the atmosphere concomitant enrichment, arises clearly from the preceding table. If the tectonic, volcanic, climatic phenomena, the sulphur, carbon, iron cycles, the terrestrial crust/ocean/atmosphere system redox state importance (Schidlowski, Eichman 1977) and many other factors could play a non-negligible role in the PO2 P.A.L. evolution, it appears, nevertheless, that the prevalent, probabilistic factor, of this evolution is the rise of the vegetable kingdom, from Archaean to our days, from Schizophyta and Thallophyta primarily watery to the Pteridophyta and Spermatophyta, primarily terrestrial, with increasing productivity. This corresponds to our probabilistic interaction model between the environmental evolution and the biological evolution.

After having highlighted the vegetable evolution probabilistic influence on an environment parameter, partial pressure PO2 P.A.L., we will study the opposite interaction, the evolution probabilistic influence of partial pressure PO2 P.A.L. on the biological and, more particularly, animal evolution.

According to the probabilistic model, the PO2 P.A.L. the rate evolution in the atmosphere, from the Archaean to our days, is a prevalent parameter, probabilistic, of the living organisms evolution, from procaryotes to the "upper" Vertebrates. We noted (II) that the vegetable evolution had considerably modified, primarily by photosynthesis, since the earth origin until today, the PO2 P.A.L. rate. Reciprocally, the organisms reacted, while evolving, with this chemical parameter rate modification of their free molecular oxygen environment. Just as the calcium, iodine elements, or others like C, S, P... or like the electromagnetic, sound waves..., oxygen can be regarded as an environment stimulus to which react the organisms. We propose that, in accordance with our model, the animal evolution is correlated, chronologically, in a probabilistic way, during geological times, with the free molecular oxygen content present in the hydrosphere and the earth's atmosphere. PO2 P.A.L. having passed, from Archaean to our days from 0 to 1 (I), it results from it that the the organisms reaction evolved, concomitantly with this free molecular oxygen stimulus variation, this evolution appearing primarily by a modification of the respiratory systems.

Oxygen is not essential to the life. In the anaerobiose, there is hydrogen transfer of an organic molecule to another (fermentative mode) whereas in aerobiosis, this transfer passes by oxygen. The breathing significant result is less the water and carbon dioxide formation that of A.T.P. By glycolysis and the fermentative way, the anaerobic cells manufacture, starting from glucose, 2 A.T.P. molecules, whereas the same reaction, continuing with breathing in the aerobic cells, produces 32 A.T.P. molecules (Krebs cycle oxydative phosphorylation) that is to say 16 times more energy (Mason 1992, Robert J.Huskey 1998).

As we evoked above (Chapter VI: The cambrian explosion), the relations which exist between free molecular oxygen and the organisms are complex. We pointed out the two principal respiratory modes: watery breathing (cutaneous and branchial) and air breathing (cutaneous, trachean and pulmonary) just as the mixed systems (tracheangills, " water pulmonary "), breathing various physical and chemical parameters (capitance, temperature, Fick law, etc...), the multiple morphological and physiological devices which improve it (lashes, whips, gills, circulatory apparatus, blood or hemolymph, respiratory pigments, etc...) (Turquier 1994).

An animal energy consumption analysis results in its oxygen uptake. This one depends, at the Vertebrates, on the heart size and the cardiac beats frequency. It is admitted that the cardiac flow is correlated with the animal oxygen uptake at rest (Turquier 1994). In the following table, we indicated, for various animals groups, the heart weight, in % of the body weight, the cardiac flow and the average oxygen consumption:

Heart weight, in % of the body weight: Fishes 0,2 - Amphibia 0,5 - Reptiles 0,5 - Mammals 0,6 - Birds 0,8 (2,56 for the Thrush - Grassé 1992).

Cardiac flow, in ml kg-1 min-1: Fishes: Teleosts 9,3, Selacia 22 - Amphibia (Urodela, Anoura) 30 - Reptiles: Iguana 44, Tortoise 55 - Mammals: Man 85, Dog 150 - Birds (Duck): 287.

Consumption O2, in ml kg-1 H-1: Cephalopods 60/120 (much less by Nautile) - Fishes (Trout) 100 - Amphibia (Frog) 70/170 - Reptiles 50 - Arachnida 13/356 - Mammals, from 210 (Man) to 7400 (Shrew) - pulmonary Gastropods (Limax flavus) 360 - Birds, hen egg 200, average 700 (Rahn, Ar, Paganelli 1986) (Turquier 1994).

With this table reading, one can make the following observations:

1) At the Vertebrates, the heart weight in % of the body weight varies in the same direction as the cardiac flow (from 0,2 to 0,8 and 9 to 287).

2) the oxygen uptake is, on average, parallel with the cardiac flow and grows, from the Invertebrates with branchial breathing to the organisms, Invertebrates and Vertebrates, with air or mixed breathing (Amphibia, Reptiles, Arachnida, Mammals, Birds and even pulmonary Gastropods).

3) It is necessary to moderate these observations by noting that, at the Vertebrates, with equal weight, the average oxygen consumption is 14 times more significant at Homeotherms than at Poikilotherms (with 20 ° C): 700 ml H-1 for a Mammal of one kg for 50 ml H-1 for a Reptile of one kg (Turquier 1994).

4) In addition, at the homeotherm Vertebrates, the oxygen quantity consumed per weight unit is all the more large since the animal is smaller: of 210 ml O2 kg-1 H-1 at the Man to 7.400 ml O2 kg-1 H-1 at the Shrew (body mass 5 g).

The evolution, the increase in PO2 P.A.L., during geological times, from Hadean to the Present one, that the preceding analyses made it possible to highlight, were not without having a determining influence on the animal life evolution. We indicated that this PO2 P.A.L. rate, environment parameter, can be regarded as a stimulus to which reacted the organisms, following the example calcium, iodine, etc... or physical factors like the electromagnetic waves, the sound waves, etc... While increasing, the PO2 P.A.L. rate opens biological process possibilities, starting from certain thresholds. Thus the 0,01 PO2 P.A.L. threshold for the protists aerobic breathing (Holland 1998) is it necessary, like the collagen, muscles production and the cutaneous respiration requires a 0,07 PO2 P.A.L. minimum (Towe 1970 - Bruce Runnegar 1982 - date of Rudolf, Elizabeth Raff).

In the table which follows, we tried to establish the correlation between 1) the earth age (of billion years), 2) the PO2 P.A.L. corresponding rate, 3) biological and respiratory processes permitted by the PO2 P.A.L. rates, 4) animal groups appearance (and protophytes) attested by their fossils. Given the documentation gaps and uncertainties, the PO2 P.A.L. rates must be considered, as we indicated higher, more like reference marks and magnitude orders than like rigorous data, and more particularly at Archaean and Proterozoic. This table is not exhaustive and can be only simplifying, given the biological phenomena complexity. It counts the chronology of the apparition of new biological and respiratory processes as its most significant species correlation. We will be able to note that this appearance of the species is not fortuitous. It is contemporary or posterior on its biological possibility date. This, which could be regarded as a self-evident truth, expresses, in fact, the relation which exists between a biological process possibility permitted by the PO2 P.A.L. rate and the organisms probabilistic reaction to the oxygen stimulus, as we proposed higher.

4,6: PO2 P.A.L. = 0 - abiotic earth's crust - earth constitution, intense volcanicity, primitive atmosphere by coat degazification, rich in methane, hydrogen and ammonia, probably carbon dioxide and water vapor (Brack, Raulin 1991).

3,80-3,85: PO2 P.A.L. = 0 - possible anaerobic biological processes - bacterial synthetic activity in the carbonated Isua sediments (Schidlowski 1988) (Mason 1992), Akilia island (Mojzsis and Arrhenius 1996), reduced carbon, autotrophic and chimiotrophes organisms, methanogenese, photosynthetic sulphur bacteria golden age (Nisbet 1987), archaebacteria (Woese 1981), unicellular (or acellulars?) organisms, ARN world? LUCA (Last Universal Common Ancestor) hyperthermophile archae? (Forterre 1997), or alive tree with primitive cells generating three primitive groups: bacteria, archaebacteria and eucaryotes (Carl Woese 1998 ; W.Ford Doolittle,1999) - procaryotic cells.

3,5: PO2 P.A.L. = 0 - possible anaerobic biochemistry and fermentation - anaerobic autotrophic microbial forms, archaebacteria, purple anaerobic photosynthetic bacteria (Margulis, Sagan 1989), first Warrawoona Australia stromatolites (North Pole) (Mason 1992), filamentous microfossils from blue and green algae (Awramik 1977), (Schopf 1991), thermoacidophiles organisms and photosynthetic eubacteria ? (Nisbet 1987), - procaryotic cells.

3,0: PO2 P.A.L. < = 0,002-0,003 - fermentation, possible aerobic biochemistry at the 0,002 pressure (Chapman, Schopf 1983) - aerobiosis beginning, oxygenates produces by photosynthesis (Schidlowski, Eichman 1977), collected by the dissolved iron in water to form ferric oxides (Wilson 1993), procaryotic microbes age who are flourishing (cyanobacteria), for the majority obligatorily photoautotrophic (Rambler, Margulis, Barghoorn 1977), (Nisbet 1987), coccoids (Boureau 1986) - procaryotic cells..

2,8-2,6: PO2 P.A.L. < 0,01 - stromatolites, blue and green photoautotrophic algae cyanobacteria precursors (Schidlowski, Eichman 1977), possible aerobic organisms (Chapman, Schopf 1983) - anaerobic photosynthesis (chemosynthesis) and aerobic with oxygen release (Schidlowski, Eichman 1977), (Schopf 1977), (Whitaker, Klein 1977), (Brack, Raulin 1991), (Holland 1998), chlorophyllian photosynthesis (Boureau 1986), ribboned iron formations, ozone layer beginning, first aerobic organisms (unicellular procaryotes), (Holland 1984), (Mason 1992), (Wilson 1993), many aerobic photosynthetic species (Margulis, Sagan 1989), photosystème II appearance (Holland 1998) - procaryotic cells.

2,5-2,3: PO2 P.A.L. < 0,01 - (B.I.F., Banded Iron Formation), uraninites; 58 spheroids microfossiles genera were listed at the Proterozoic beginning (Holland 1984), (Boureau 1986), (Mason 1992) - procaryotic cells. .

2,0: PO2 P.A.L. = > 0,01 - possible anaerobic and aerobic organisms with fermentation and breathing (Krebs cycle), (Chapman, Schopf 1983) - stromatolites, ozone layer reinforcement (Margulis 1977), anaerobic and aerobic organisms Gunflint Chert B.I.F., filamentous procaryotic cells (Gunflintia minuta) and coccoids, (Tyler, Barghoorn 1954), abundant aerobic procaryotic blue algae, 10 microns in diameter, similar to present Nostocs , 18 species known flora arranged in 14 genera (Boureau 1986), purple and green photosynthetic microbes, with oxygen optional production, A.T.P. production by the present cyanobacteria aerobic ancestors (Margulis, Sagan 1989), (Holland 1984), (Mason 1992) - procaryotic cells.

1,9-1,5: PO2 P.A.L. > 0,01 - the hematite red layers, (FeO3) appearing towards 2,00 indicate oxydative atmosphere conditions and lead to the B.I.F. disappearance towards 1,8-1,7 and the ozone layer O3 development (Levin). The increase in the molecules O2 in the atmosphere allows the oldest known aerobic eucaryote cells emergence, approximately 1,9 B.Y. old (Gryptania spiralis - Pan Terra 1996); 0,01 PO2 P.A.L. threshold for the protists aerobic breathing (Holland 1998); cells increase, acritarchs (40 to 60 microns in diameter), mitosis and meiosis appearance, A.T.P. production by Krebs cycle oxydative phosphorylation, genetic recombinations (Boureau 1986), endosymbiose?, (Schopf 1977), (Margulis, Sagan 1989), (Danchin, Debrenne 1992), eucaryote algae (Wilson 1993) - eucaryote cells.

1,5-0,565: PO2 P.A.L. > 0,01 = < 0,07 - acritarchs radiation towards 0,900-0,850 then quasi-disappearance towards 0,600; unicellular green eucaryote algae first fossils equipped with distinct chloroplasts; multicellular plants first fossils with structures similar to salads and kelps (1,4-1,2 Butterfield 1998); increase in the eucaryote microflore and reduction in the procaryotic microflore, in particular because of the eucaryotes greatest capacity to use available phosphate (Lehman, Botkin, Likens 1975), (Holland 1984); Montana multicellular algae, tracks and burrows traces (Coelomates?) (Babin 1991) - eucaryote algae era.

0,565-0,544 (Vendian): PO2 P.A.L. > 0,07 = < 0,10 - phytoplankton dynamic evolution involving an increase in the atmospheric oxygen level right before the metazoa macroscopic fauna appearance with soft body of Ediacara at the Precambrian end (Knoll 1996), (Hoffmann, Kaufman, Halverson 1998), (Heinrich D. Holland 1998); ediacarian metazoa fauna production possibility with soft body which requires, for the collagen, the muscles production and the cutaneous respiration (marine worm Dickinsonia: 1 meter length for a 6 mm maximum thickness), a 0,07 PO2 P.A.L. minimum (Towe 1970 - Bruce Runnegar 1982 - Rudolf, Elizabeth Raff); symbiotic relations between photosynthetic algae and animal organisms (Hallock-Muller) - 25 species and 15 genera Ediacara fauna belonging to 3 phyla: Cnidae majority (Coelenterata 67 % of which the three quarters are medusoids organisms, " jellyfishes era "), Annelida (25 %, Dickinsonia), Arthropoda (5 %) and incertae sedis (Cloud, Glaessner 1982), stromatolites built by the blue and green algae regression (Avramik 1977); metazoa with soft bodies, first metazoa with calcium phosphate and carbonate shells among the most recent fossils - diploblastic and triploblastic metazoa.

0,544 to 0,505 (Cambrian) PO2 P.A.L. = > 0,10 : possible cutaneous and branchial watery breathing; many biological innovations, coelomic circulation, hemal or blood circulatory apparatus, respiratory pigments, calcium phosphate and/or carbonate exoskeleton secretion, intense phosphogenese; Cambrian "fossiliferous explosion", from Tommotian to middle Cambrian, with the sub-kingdoms and faunas diversification with increasingly varied shells and exoskeletons, rich in calcium carbonates and phosphates (Spongiae, Archeocyata, Cnidae, Brachiopods, Molluscs, Arthropoda, Echinodermata, etc...), cf Chapter VI "the cambrian explosion" (Stanley 1976, Rhoads, Morse 1971, Brasier 1979, Conway Morris 1982, Valentine 1986, etc...); possible first terrestrial spores, (Brasier 1979), (Bengtson, Conway 1984); " Thallophyta era " (British Columbia, Conway Morris and Robinson 1988); radiations: approximately 400 genera, 120 families (Devillers and Chaline 1989).

0,505 to 0,438 (Ordovician): PO2 P.A.L. = > 0,10 : The terrestrial life first appearance would go up in middle Ordovician where terrestrial spores traces are found (0,449/0,458 B.Y. Jane Gray) but not from vascular plants.The first spores would be perhaps dated from Cambrian. The first terrestrial vascular plants Crytogames, the Protopsylophytes, would date from higher Ordovician (Auboin, Brousse, Lehman 1985), (Babin 1991). Many plants and animals species adaptive radiations; at the Ordovician end one counts approximately 1400 genera and 470 primarily marine metazoa families (Devillers and Chaline 1989). The PCO2 P.A.L. level before 0,440 B.Y. would have been higher 16 to 18 times its present level (Crayton J.Yapp 1998). First marine scorpions (Eurypteride - Petrunkevitch 1960, Wills, Briggs and Fortey 1994). First established Vertebrates (Sacabambaspis, Agnatha of higher Ordovician - Gagnier 1986).

0,438 to 0,408 (Silurian): PO2 P.A.L. > 0,13 : If the terrestrial plants and animals possibility is problable in Ordovician, their obviousness is established in higher Silurian. The terrestrial vascular plants development and the O2 terrestrial photosynthetic production supplants the primarily marine photosynthetic production former to Silurian (Holland 1984). First vascular plants fossils, the Psylophytes (Cooksonia) and the Lycopodophytes (Baragwanathia?) attest increase in the photosynthesis which grows considerably on the continents (Theobald, Gama 1969), (Auboin, Brousse, Lehman 1985), (Babin 1991). Development in Silurian then explosion in Devonian of the Pteridophyta vegetable cover, " vascular Cryptogams era ", primarily terrestrial plants, with photosynthetic productivity double that of the sea plants (Whittaker, Likens 1975; Mc Lean 1978); fall fast of PCO2 P.A.L. (Berner 1994) and concomitant increase in PO2 P.A.L. (Crayton J.Yapp 1998). Air breathing possibilities (atmospheric gas oxygen absorption and not only dissolved in water) with the increase in PO2 P.A.L. Mushroom fossils are counted (ascomycete) (Taylor and Taylor 1993). Pulmonary and tracheans apparatuses first appearance at the Vertebrates and the Invertebrates. First Invertebrates fossils with air breathing, Arachnida (oldest known, a trigonotarbide gone back to 0,414 with pulmonary respiration - Petrunkevitch 1960), marine scorpions (higher Silurian Palaeophonus) (Moret 1966), (Theobald, Gama 1969), (Grassé 1993), (Taylor and Taylor 1993); myriapoda. Exoskeletons and endoskeletons secretion, swim bladder acquisition at Actinopterygia (higher Silurian) which will become a pulmonary at Dipnoi in Devonian (Babin 1991), (Grassé 1992).

0,408-0,360 (Devonian): PO2 P.A.L. 0,65 to 0,74 - Antiquated Pteridophyta Development (Rhynia - Aglaophyton major) in the Scottish marshes (Jean Broutin 2000). Various modes of air, cutaneous, pulmonary, trachean, mixed breathing simultaneous diversification. " Explosion ", starting from Devonian, of air breathing in the Metazoa groups majority and particularly at the Arthropoda and the Vertebrates (Turquier 1994). Air breathing develops at the same time on earth and in the aquatic environments.

In the Arthropoda, at Chelicerata as at Antennata, 4 classes out of six adapt to air breathing: 1) Arachnida (Acarina, Protocarus Crani of Devonian, Theobald, Gama 1969; Spiders with tracheo-pulmonary respiration of Devonian, Babin 1991, Grassé 1993); 2) Shellfishes (Malacostraceous: Isopoda, Woodlice, Old Red Sandstones Praearcturus with pseudo-tracheas, Theobald, Gama 1969, Grassé 1993); 3) Myriapoda (Diplopoda, devonian Archipolypoda, probably amphibia, Grassé 1993; Archidesmus, Moret 1966); 4) Apterygota Insects (Collemboles with transtegumentary breathing, Grassé 1993; middle Devonian Rhyniella of Rhynie, Moret 1966); Pterygota Insects (middle Devonian Rhyniognatha hirsti of Rhynie, Theobald, Gama 1969); Devonian marine pulmonary Gastropods (Moret 1966).

In the Vertebrate sub-kingdom, among Gnathostoma, in 2 classes, organisms will develop with a mixed breathing (gills and pulmonary) in Devonian. The 3 other classes, with entirely air breathing, will appear later, when the atmospheric PO2 P.A.L. rate increases: 1) Fishes : Selacia, Arthrodians Placodermi of middle Devonian (Coccosteus) and superior (Phyllolepis) with gills and pulmonary breathing; middle Devonian Crossopterygii (Latimeria chalumnae with ossified swim bladder and nonfunctional pulmonary outline, Grassé 1992); lower Devonian Rhipidistians with manners amphibia (Osteolepis, Theobald, Gama 1969); Sarcopterygii (lower Devonian Dipnoi, Maisey 1996; Dipnorhynchus with gills and pulmonary breathing , Theobald, Gama 1969); 2) Amphibia (higher Devonian Old Red Sandstones, Stegocephalia, Ichthyostega with air breathing, oldest tetrapode known, Theobald, Gama 1969, Babin 1991, Pamela Gore 1997). The tetrapoda, equipped with air breathing, start to conquer the earth from 0,360. Close relations of pulmonary fishes, they are divided into 2 groups, the Amphibia with mixed and cutaneous breathing and Amniotes (Reptiles, Mammals and Birds) with entirely air breathing.

0,360-0,295 (Carboniferous) PO2 P.A.L. 0,93 : trachean and pulmonary respiratory possibilities blooming - Among Amniotes with entirely pulmonary breathing, Vertebrates class appearance , the Reptiles (Cotylosauria - superior Carboniferous Diadectes, middle Carboniferous Hylonomus; Pelycosauria - superior Carboniferous Varanosaurus - Theobald, Gama 1969, Babin 1991). Among the Invertebrates, Pterygota Insects with trachean breathing rise (Paleopteran: Paleodictyoptera, Ephemeroptera, Odanotoptera, Stephanian Megasecoptera; Neoptera: Stephanian Protorthopteroids, inferior and middle Westphalian Blattopteroids, Theobald, Gama 1969). The Insects presently represent 80 % of the alive animal species. In the Molluscs, terrestrial Gastropods with pulmonary respiration emergence which will develop until the Present one (Stylommatophores, Dendropupa, Zonites, Theobald, Gama 1969). Nemathelminthes remainders are known with Carboniferous (Theobald, Gama 1969) - certain Nematodamorpha with cutaneous air breathing have teguments with exoskeleton (Turquier 1994).

0,295-Present (Permian, Mesozoic, Cenozoic): PO2 P.A.L. 1 - Complete present air respiratory possibilities - "superior" Vertebrates: Mammals (terminal Triassic, Rhetian, pulmonary respiration with intense bronchial and alveolar ramifications, Grassé 1992), Birds (superior Jurassic, Archaeopteryx, complex bronchial system and air bags), more powerful air breathing at these amniote homeotherm Vertebrates, in connection with their needs more significant than at amniote poikilotherm Vertebrates (Reptiles) (see higher). Invertebrates: Annelida (terricol Oligochaeta, Lombric or Earth Worm, transtegumentary air breathing, superior Jurassic?; Achaeta, Hirudinea of the Eocene) (Turquier 1994), (Theobald, Gama 1969). Arthropoda, land Decapoda Crustacean (Coenobita, Birgus latro, Cretaceous, mixed, gill and pulmonary breathing) Theobald, Gama 1969), (Turquier 1994).

Certain PO2 P.A.L. thresholds make possible the emergence of biological innovations , new anatomical structures and physiological processes. This emergence is contingent. The eucaryote cells aerobic breathing simple possibility does not involve necessarily their appearance. It is the probability, i.e. the events prevalence where the mathematical chances are high which transforms the contingency into the most probable event and, by extension, actually. We propose that the probabilistic interaction model between the environmental evolution and the biological evolution is this transformation vector. It is the probability theory which modifies the simple possibility into reality. The favorable factors existence to the aerobic breathing or the cutaneous respiration emergence involves thus, according to the probabilistic model, their appearance, in accordance with their high chances.

a) The PO2 P.A.L. rate growing enrichment during geological times is concomitant with the different animal taxa chronological appearance, in connection with the requirements out of O2 for their metabolism, from the protists to the most demanding metazoa, the Birds. We will specify low, in chapter 2, this chronology with the PO2 P.A.L. principal thresholds examination.

b) The darwinian theory accounts for the evolution by the couple mutations/selection. This couple relates to primarily the micro-evolution, i.e. the specific evolution, with random transfers and the favorable transfers to the species selection. This model does not have the capacity to bring a organisms macro-evolution valid explanation, parallel with the PO2 P.A.L. rate growth.

c) The macro-evolution, concomitant with the PO2 P.A.L. rate evolution, concerns, simultaneously, taxa, from the very distant sub-kingdoms, Invertebrates like Vertebrates, protozoa as well as metazoa. It is about a collective macro-evolution. Nothing, in the darwinian model, makes it possible to give an account of these simultaneous collective phenomena.

d) The collective macro-evolution in time, concomitant with the PO2 P.A.L. rate evolution, is also in space. Indeed, the taxa evolve as well on earth as in water with the PO2 P.A.L. rate growth: in Devonian, marine scorpions, amphibious myriapoda, marine pulmonary gastropods, terrestrial arachnida and insects; fishes with gills and pulmonary breathing, Arthrodians, Rhipidistians, Sarcopterygii, Amphibia with air breathing, Stegocephalia, Ichthyostega. Here either, the darwinian model does not have sufficient explanatory capacity.

According to the probabilistic model, the biological evolution proceeds under the environmental factors probabilistic influence and, in the event, under that of the PO2 P.A.L rate increase, during geological periods,.The evolution passes by a certain decisive stages number, conditioned by what one can indicate under the thresholds term. These thresholds are the minima from which the organisms, protozoa or metazoa, have the possibility to appear. This emergence possibility is transformed into reality by the means of the mathematical chances of the probability theory. These mathematical chances are objective, neutral, contrary to the darwinian advantages, utilitarian and anthropocentric. In the following diagram, the correlation between the PO2 P.A.L. biological thresholds appearance (chronology in million years) and the morphological and/or physiological innovations or organisms emergence is highlighted.

PO2 P.A.L. = > 0,01 - 2.000 - 0,01 PO2 P.A.L. threshold for the protists aerobic breathing (Holland 1998) - oldest known aerobic eucaryote cells emergence towards 1.900 (Gryptania spiralis - Pan Terra 1996).

PO2 P.A.L. > 0,07 = < 0,10 - 565 - 544 (Vendian): Metazoa production threshold with soft body which requires, for the collagen, muscles production and the cutaneous respiration (marine worm Dickinsonia), a 0,07 PO2 P.A.L. minimum (Towe 1970 - Bruce Runnegar 1982 - Rudolf, Elizabeth Raff); metazoa ediacarian fauna with soft body, first metazoa with calcium phosphate and carbonate shells among the most recent fossils - diploblastic and triploblastic metazoa.

PO2 P.A.L. = > 0,10 - 544 to 505 (Cambrian): Watery cutaneous and gill breathing threshold, many biological innovations, coelomic circulation, hemal or blood circulatory apparatus, respiratory pigments, biomineral respiratory pigments threshold, calcium phosphate and/or carbonate biomineralization and exoskeleton secretion threshold (Bacescu 1963), (Emery, Hülsemann 1961), (Hartman 1955, 1966), (Rhoads, Morse 1971), (Tunnicliffe 1981); Cambrian "fossiliferous explosion", from Tommotian to middle Cambrian, with the sub-kingdoms and faunas diversification and increasingly varied shells and exoskeletons, rich in calcium carbonate and phosphate (Spongiae, Archeocyata, Cnidae, Brachiopods, Molluscs, Arthropoda, Echinodermata, etc...), (Stanley 1976, Rhoads, Morse 1971, Brasier 1979, Conway Morris 1982, Valentine 1986); radiations: approximately 400 genera, 120 families (Devillers and Chaline 1989).

PO2 P.A.L. > 0,13 - 438 to 408 (Silurian) - PO2 P.A.L. 0,65 to 0,74 - 408 to 360 (Devonian): Air breathing threshold (oxygen atmospheric gas absorption and either only dissolved in water) with the increase in PO2 P.A.L. in Silurian. Pulmonary and trachean apparatuses first appearance at the Vertebrates ones and the Invertebrates. Invertebrates with air breathing first fossils, arachnida (oldest known, a trigonotarbide gone back to 414 with pulmonary respiration - Petrunkevitch 1960), marine scorpions (higher Silurian Palaeophonus) (Moret 1966), (Theobald, Gama 1969), (Grassé 1993), (Taylor and Taylor 1993); myriapoda. Swim bladder acquisition at Actinopterygia (higher Silurian) which will become a pulmonary at Dipnoi in Devonian (Babin 1991), (Grassé 1992).

In Devonian, with a PO2 P.A.L. rate carried with 0,68/0,74, the air various modes, cutaneous, pulmonary, trachean, mixed breathing simultaneous diversification, become possible. " Explosion ", starting from Devonian, of air breathing in the metazoa groups majority and particularly at the Arthropoda and the Vertebrates (Turquier 1994). Air breathing develops at the same time on earth and in the aquatic environments. In the Arthropoda, at Chelicerata as at Antennata, 4 classes out of six are adapted to air breathing: 1) Arachnida 2) Shellfishes 3) Myriapoda 4) Insects.

In the Vertebrates sub-kingdom, in 2 classes, organisms will develop with a mixed breathing (gills, cutaneous and pulmonary) in Devonian: 1) Fishes 2) Amphibia. The 3 other classes, with entirely air breathing, will appear later, when the atmospheric PO2 P.A.L. rate increases again.

PO2 P.A.L 0,93 - 360 to 295 (Carboniferous): Trachean and pulmonary respiratory possibilities blooming - Among Amniotes with entirely pulmonary breathing, a Vertebrates class appearance, the Reptiles. Among the Invertebrates, Pterygota Insects with trachean breathing rise. In the Molluscs, terrestrial pulmonary Gastropods emergence with pulmonary respiration which will develop until the Present one.

PO2 P.A.L. 1 - 295 - Present (Permian, Mesozoic, Cenozoic): Complete present air respiratory possibilities - "superior" Vertebrates chronological emergence, according to their requirements level out of O2: Mammals at higher Triassic (Rhetian), pulmonary respiration with intense bronchial and alveolar ramifications, Birds at superior Jurassic (Archaeopteryx), complexe bronchial system and air bags. Air breathing, more powerful at these homeotherm amniote Vertebrates, is in connection with their needs more significant than at poikilotherm amniote Vertebrates (Reptiles) appeared at Carboniferous.

a) Taxa with air or mixed breathing phyla seniority and late emergence

The probabilistic correlation, between the PO2 P.A.L. thresholds and biological and respiratory processes that they make possible, and the taxa concomitant or posterior appearance using these new processes is clearly highlighted in the preceding table. This correlation between the PO2 P.A.L. evolution, that of the biological processes and the respiratory systems that it allows, and the animal evolution, is corroborated by the taxa with air breathing examination. If the watery Vertebrates appearance possible in Cambrian and is proven in Ordovician (Ostracodermi), the forms with mixed or air breathing (Fishes, Amphibia, Reptiles, Mammals and Birds) are known only from Devonian and later on (0,67 to 1 PO2 P.A.L.). Concerning the Invertebrates, the correlation is also obvious. The sub-kingdom adapted best to air breathing, that of the Arthropoda, is known in the aquatic environment since basal Cambrian (Trilobites, Crustacean Ostracods, Malacostraceous - Cambrian Ceratiocaris and Hymenocaris) (Theobald, Gama 1969), whereas 4 classes out of 6 are adapted to air breathing only since Devonian (Arachnida, Isopoda Crustaceous, Myriapoda and Insects). One does not count air breathing Annelida (Oligochaeta or Achaeta) (Theobald, Gama 1969) that since Mesozoic whereas the sub-kingdom exists since the Precambrian one (Ediacara fauna) (Cloud, Glaessner 1982). Among Molluscs, the Gastropods class is known since lower Cambrian (Amphigastropoda, Tryblidiata, Bellerophontata), whereas pulmonary Gastropods, with air breathing, are it only since Devonian (marine) or the Carboniferous (terrestrial) (Theobald, Gama 1969).

b) Taxa with mixed breathing in the intertidal mediums

The intertidal systems exist since the Precambrian and the Gastropods and Shellfishes classes with watery breathing since lower Cambrian. However, the intertidal organisms with mixed, watery and/or air breathing, are listed only since Devonian and later on (Molluscs: Prosobranchia, Opisthobranchia and Pulmonary Gastropods; Arthropoda: Decapoda Paguroide Shellfishes of Mesozoic) (Theobald, Gama 1969), (Turquier 1994). Thus, even in this very particular ecological system, only a significant increase in the PO2 P.A.L. rate at Devonian allows the release, starting from a certain threshold, by the probabilities, the emergence of the taxa with air breathing.

The examination of the biological evolution, concomitant with the increase in PO2 P.A.L., during various geological times, enabled us to note, thanks to many facts, the probabilistic model explanatory and predictive capacity.

This model highlighted chronological emergence of certain groups of animals, from what we proposed to call the thresholds rule: this rule expresses the relation which exists between the biological process possibility permitted by the PO2 P.A.L. rate and the organisms probabilistic reaction to the oxygen stimulus.

At the superior Archaean, the oxygen absence in the atmosphere authorizes only the anaerobic procaryotic organisms existence. Later, the beginning of the presence of a small atmospheric oxygen quantity (0,002 to 0,003), makes possible aerobiosis with the emergence of obligatory or optional aerobic procaryotic organisms.  

The 0,01 PO2 P.A.L rate, reached towards 2 B.Y., seems necessary to the aerobic eucaryote cells operation, which appear roughly at that moment.

The 0,07 to 0,10 PO2 P.A.L. rate, reached towards 565 M.A., necessary to the soft body organisms construction (conditioned by the collagen fibres, sterols, fatty acids, and muscles development) then exoskeletons organisms (conditioned by the biomineralization threshold) corresponds to the vendian fauna appearance followed by the "cambrian explosion".

The PO2 P.A.L. rate reached at the Silurian end (0,408 B.Y.), > 0.13 < 0.67, seem to start to allow absorption, by the organisms, until there strictly watery, of the atmosphere oxygen (marine Scorpions). In Devonian (0,408 to 0,360 B.Y.), where the PO2 P.A.L. rate reaches approximately the 2/3 of the present rate, air breathing can open out in 2 principal respiratory systems: the pulmonary system at the Vertebrates (still mixed, watery and air breathing at Fishes - Dipnoi - and the Amphibia - Stegocephalia -) and the trachean system in the Invertebrates (particularly at the Arthropoda, 4 classes out of 6). These 2 great systems can be combined (trachean - Arachnida pulmonary breathing) or be reversed (Pulmonary Gastropods pulmonary at Carboniferous).

From Devonian dates rise from the air breathing organisms, which will develop until the Present one, parallel to the increase in the PO2 P.A.L rate which grows from 0,67 to 1. The organisms have the present pulmonary and trachean posssibilities. The Vertebrates with entirely air breathing emerge, in their increasing oxygen consumption chronological order (Reptiles to the terminal Carboniferous, Mammals at higher Triassic, Birds at the superior Jurassic). The Invertebrates, with trachean breathing, open out from Carboniferous (Insects, which represent 80 % of the present animal species). In the same way, pulmonary terrestrial Gastropods, listed from Carboniferous, develop until our days. From Annelida, Oligochaeta (Lombrics), with cutaneous air breathing, would date from the superior Jurassic. In the same way, from Hirudinea would date from the Eocene. In the decapoda Shellfishes, Paguridae, with mixed breathing, are represented from the Cretaceous.

The respiratory systems development chronology, aerobic, watery (cutaneous and gills) then air (cutaneous, trachean and pulmonary) among protists (eucaryote cells) then the metazoa (vendian fauna, Vertebrates and Invertebrates with air breathing) cannot be regarded as fortuitous. As it could be noted in the preceding chapters, it is parallel and concomitant with the PO2 P.A.L. evolution. It concerns, simultaneously, most of the taxa. One can thus consider, rightly, that the emergence of the various respiratory systems common denominator is the PO2 P.A.L. rate. Maybe, probably, around 0,01 for the breathing protists, approximately 0,07 for cutaneous watery breathing, from 0,10 to 0,16 for gill breathing and probably towards 0,67 for air breathing.

In conclusion, the whole of the preceding facts validates our probabilistic interaction model third application between the environment parameters evolution and the animal taxa evolution. The molecular oxygen free rate PO2 P.A.L. is one of these parameters. It can be regarded as a stimulus to which the organisms react. Parallel to its increase, in a probabilistic way, the biological (procaryotic cells, eucaryote cells, protozoa, metazoa, exoskeletons and endoskeletons) and respiratory (cutaneous, gills, pulmonary and trachean) systems are evolving.