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Gaia nel tempo e nello spazio

Risulta molto suggestivo considerare la Terra come un organismo vivente anche quando si cerca di ripercorrerne la storia fino alla comparsa della specie umana. In questo modo è possibile descrivere il contesto sia temporale che spaziale nel quale l’uomo si ritrova oggi a dover inevitabilmente compiere delle scelte (etiche e politiche). Gli studi dei paleontologi ci dimostrano che i fossili dei primi elementari esseri viventi risalgono a circa 3,5-4 miliardi di anni fa. Questa è, al momento, l’età che possiamo attribuire a Gaia. In realtà, il pianeta esisteva già da tempo. I dati a disposizione oggi fanno risalire la formazione della Terra a 4,5 miliardi di anni fa, mentre quella del Big Bang (teoria attualmente più accreditata sulla formazione dell’intero Universo) a circa 13 miliardi di anni fa. Sappiamo che esistono miriadi di galassie e che ciascuna è costituita da miriadi di sistemi solari che contengono diversi pianeti. Non sappiamo al momento se esistano altri pianeti viventi oltre al nostro. Quello che si può affermare è che, in ogni caso, la vita ha fatto la sua comparsa quando le condizioni chimico-fisiche del nostro pianeta lo hanno permesso. Da questo punto in avanti è partito un inesorabile processo di evoluzione che, in seguito alle continue interazioni e mutue trasformazioni tra organismi viventi e contesto ambientale, ha prodotto l’enorme varietà biologica e di habitat che oggi osserviamo.

A cura di Alice Benessia, Maria Bucci, Simone Contu, Vincenzo Guarnieri.

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