Dalla Terra alla Luna è la nuova rubrica di Cronache Maceratesi Junior per migliorare l’inglese imparando nuove cose sul nostro territorio. Grazie a una super insegnate, Barbara Innocenti, biologa e mamma che ha vissuto per oltre 20 anni negli Stati Uniti andremo alla scoperta dei segreti delle Marche… in inglese! Come un viaggiatore spaziale che va sulla Luna e ritorna sulla Terra con un sacco di cose da raccontare così anche Barbara è tornata nelle Marche dopo aver scoperto tante cose negli States e ora vuole condividerle con te. Sei pronto per questa entusiasmante avventura? Allora preparati, in questa prima puntata andremo sul monte Conero per fare un viaggio nel tempo di “solo” 90 milioni di anni!
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Chi non ha mai sognato di essere protagonista del film Jurassic Park? Di poter tornare indietro nel tempo e vedere branchi di dinosauri pascolare tranquilli in una pianura o combattere ferocemente tra di loro? Chi non ha desiderato, più semplicemente, di imbattersi in un fossile, un osso o un’orma di dinosauro, magari lungo un sentiero sterrato sulle nostre bellissime colline marchigiane? Purtroppo neppure quest’ultimo desiderio si realizzerà mai e vi spiegheremo perché. Vi spiegheremo anche come una passeggiata sul Monte Conero vi permetterà di viaggiare indietro nel tempo, fino a 90 milioni di anni fa. Potrete vedere, osservare, quasi toccare le rocce che 65 milioni di anni fa, alla fine del Cretaceo, assistettero alla morte dei dinosauri e di circa l’80% delle specie animali. Troverete le rocce del Terziario in cui la vita rincominciò dalle sue forme più semplici per culminare nell’evoluzione dell’Uomo. Soprattutto potrete vedere il tanto famoso quanto raro livello K-T, un sottilissimo strato di rocce, esattamente a cavallo tra Cretaceo (K) e Terziario (T), che contiene le prove della caduta sulla terra di un meteorite gigantesco che secondo gli scienziati spazzò via i dinosauri.
Fossils are any residue of ancient life that was buried in the ground and that with the action of time, temperature and pressure transformed within rock. Fossilized residues such as bones, teeth, plants, footprints, sometimes even dung, last meals and microorganisms can all tell us a story about the ancient past as the residues are hidden within the rock which acts to preserve them. The rock is needed to protect fossils but it also prevents us from finding them. To locate fossils the rock needs to erode a bit to expose back the residue. This can occur by atmospheric or water erosion of the rocks or other geological events such as earthquakes and plaque tectonics. Unfortunately those same events can occasionally destroy fossils forever.
If we want to find dinosaur fossils or want to know about life at their time, we must first find a place where rocks of the right age are exposed and well preserved. Since dinosaurs lived between 252 and 65 million years ago, we need to find rocks belonging to that range of time. On Monte Conero, in the Regional Natural Park of Monte Conero, along a path known as ‘sentiero di San Lorenzo’ there is a wall, about 10 meters high, exposing rocks dated between 90 and 55 million years. 90-65 million years ago covers a segment of time of the so called Cretaceous period, the last period in which dinosaurs lived. These oldest rocks are found at the bottom of the wall and are whitish in color. 65-55 million years ago coincides with the beginning of the so called Tertiary period, when dinosaurs had disappeared and new species of animals took over their old habitats. These more recent rocks are positioned higher in the wall and have a light-grey color or hue. Can we find dinosaur bones in the bottom within the white part of the rock wall? No, we cannot. During the Cretaceous period, Marche was underwater. It was actually a sea and thus no land animal can be found. The pattern displayed by the rock wall, made by horizontal bands, one on top of the other, tells the story of a continuous sedimentation of plankton and debris that slowly accumulated at the bottom of the sea.
Even if devoid of dinosaur fossils, the ancient sea keeps a record of the event that killed the dinosaurs. Between the white bottom part and the grey top part, there is very thin layer, less than 1 cm thick, called the K-T boundary. It formed about 65 million years ago, marking the end of the Cretaceous (K) period and the beginning of the Tertiary (T) period. It is rare because it is exposed and well preserved only in a small number of places around the world. What characterizes it is the unusual high concentration of iridium, an element very rare in terrestrial rocks but abundant in meteorites and asteroids. Scientists think that the K-T boundary contains the residues of a giant asteroid that impacted the Earth at the end of the Cretaceous and scattered its debris all over the Earth surface, both on land and sea. The impact started a chain of events that resulted in the death of dinosaurs and about 80 % of all living forms.
Besides preserving the K-T boundary, the site on Monte Conero keeps a record of the devastating consequences of the meteorite’s impact on marine life. The rocks contain microfossils, fossils of microorganisms that lived million years ago. The size, type and number of species are different in the white versus the grey zone. Already at the magnification provided by a good hand lens, the gravel coming from the white zone shows a more variegated content that the gravel coming from the grey zone. To conclude, What does Marche have to do with dinosaurs? Nothing. What does Marche have to do with the extinction of the dinosaurs? A lot, since it keeps a clear and visible geological record of the event that determined their extinction. For this, Monte Conero is not only a beautiful terrace on the Adriatic Sea. It is a rare outdoor Natural Museum, free of charge to everyone, accessible even to children along the easy hiking path of the ‘sentiero di San Lorenzo’.
