Scientists have discovered a string of submerged islands between the Cabo de Gata (Almería province) and what is now the Spanish city-province of Melilla on the northern Moroccan coast, close to the Algerian border.
These islands are close enough together that, before they were reclaimed by the sea, would have acted as a ‘footbridge’ between the continents of Europe and Africa.
The volcanic archipelago across the Alborán Sea was created through eruptions around 10 million years ago and served as a bridge between the continents for animals between five and six million years ago.
Soon after this, the gradual disappearance of volcanic activity in the region and the cooling of the earth’s crust across the European and African tectonic plates meant the islands began to be covered by the sea, disappearing altogether beneath the water some 1.8 million years ago.
Dr Guillermo Booth-Rea of the Andalucía Earth Sciences Institute and a member of Spain’s High Council for Scientific Research (CSIC) says the ‘bridge’ would have led to ‘an exchange of fauna’ between Africa and Europe, with ‘camels and rabbits’ mostly using it.
Dr César Ranero of the CSIC and the Institute of Sea Sciences, co-author of the study – which has been published in the periodical Scientific Reports – says this bridge was key in making south-eastern Europe a habitat for creatures less likely to be seen outside the tropics.
DNA and RNA (ribonucleic acid) samples from western Mediterranean species show they are distantly related to African species, the study shows.
Some of these include lizards and geckos, which would have migrated gradually from Algeria, Morocco and even Tunisia to south-eastern Spain.
The bridge also acted as a barrier between the Atlantic Ocean and the Mediterranean Sea, preventing their waters mixing and leading to very diverse flora and fauna in each, Dr Booth-Rea explains.
This eventually led to what is known in geological history as the Salt Crisis, where the Mediterranean almost became a giant freshwater lake due to salt from the Atlantic not reaching it.