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lyudmila [28]
3 years ago
11

True Or False? the total amount of matter on earth changes significantly over geological time scales, roughly every 300,000,000

years.

Biology
1 answer:
zaharov [31]3 years ago
3 0

The rate of atmospheric CO2 has never been as low as today and the temperature / CO2 content relationship is still poorly understood Since the Earth existed, that is to say 4.567 billion years ago [1 ], if it is indeed a constant is that it never remained fixed as it was, and that it was constantly deeply modified in a rather random way. This concerns as much the internal processes (in particular the composition of the lithosphere and the variations of the mechanisms affecting the continental drift) as the external processes

Among the latter, the atmosphere has not ceased to vary completely, particularly with regard to its gaseous composition. All of these internal and external processes have continually 'telescoped' and have led to complex feedbacks at the root of the many climate changes observed in the geological record. To these parameters are also added those piloted at the extraterrestrial scale, among the most important are the activity of the Sun or the variations of the orbital parameters of our Planet (precession, obliquity, ecliptic). The result is an extremely complex combination of regular cumulative processes, irregular, linear or not, often chaotic, playing at all time scales and affecting at any time the climate that constitutes an answer. Physicists, chemists, biologists, geographers ... geologists try each one from his pre-square to unravel this skein particularly difficult to understand. The synergies between the disciplines are fortunately numerous and the climate system is gradually exposed through the geological time.

L'étude du climat actuel semble plus simple que celle des paléoclimats, il s'agit cependant également d'une situation complexe vu l'importance des paramètres mesurables et mesurés qui contribuent à établir la dynamique de notre atmosphère aujourd'hui. L'étude de l'atmosphère est donc bien un des points incontournables pour qui veut comprendre un système climatique, elle est en prise directe avec la partie interne de la Terre (exemple des volcans, de l'érosion continentale suite aux orogenèses ou formations des chaînes de montagnes…), avec la partie externe ou superficielle (exemple des océans, des forêts…) et la composante extraterrestre (exemple des flux des rayons galactiques cosmiques, des impacts de météorites …). Nombre de ces paramètres sont cernés de manière satisfaisante depuis que la Terre existe. Cette connaissance débute avec le modèle du ‘paradoxe du Soleil froid' ou hypothèse astronomique du Soleil pâle[2].

Les premières atmosphères, des réservoirs de gaz à effet de serre

Ce modèle d'évolution du Soleil prédit que sa luminosité était plus faible de 25 à 30% de l'Hadéen à l'Archéen, soit d'environ 4,6 à 4,0 Ga (Ga = milliards d'années). Si l'on considère que la Terre possédait durant cette période une atmosphère semblable à la nôtre il faudrait alors attendre 2 milliards d'années (donc jusqu'au début du Paléoprotérozoïque) pour que sa température de surface dépasse 0°C, la température initiale à 4,6 Ga étant comprise entre -43 et -23°C suivant le modèle du ‘paradoxe du Soleil froid'. La quasi-totalité des océans aurait dû être couverte de glace. Les géologues n'ont jamais relevé de trace de glaciation globale durant cette longue période excepté quelques glaciers locaux à 2,9 Ga (glaciation ‘pongolienne') et à 2,4 Ga (glaciation huronienne). Ils concluent bien au contraire à une période chaude comme en témoignent notamment la présence de cyanobactéries à 3,8 Ga[3] et d'un cycle érosif de l'eau déjà actif ayant mené à l'accumulation de petits cristaux de zircon il y a 4,4 Ga[4]. L'eau était donc déjà présente 160 Ma (= millions d'années) après la formation de la Terre et les températures océaniques déduites des isotopes de l'oxygène et du silicium mesurés sur des roches siliceuses variaient entre 30 à 50°C (Archéen et Paléoprotérozoïque) bien loin d'un climat qui aurait du être globalement très froid comme le laisserait supposer un ‘Soleil pâle' de faible luminosité.

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