VITA E METEORITI

Otto amminoacidi presenti in alcuni meteoriti rinvenuti sulla Terra testimoniano che la vita si è originata dallo spazio. Lo afferma Steve Macko, docente di scienze ambientali presso l’università della Virginia, Usa. Lo studioso ha analizzato alcune condriti carbonacee, rocce di natura meteoritica costituenti l’85% del materiale cosmico presente sulla superficie terrestre. In esse ha rinvenuto otto amminoacidi identici a quelli riscontrabili sul nostro pianeta. Secondo Macko è questa la prova che in passato sulla Terra precipitarono numerosi meteoriti di questo tipo che innescarono i primi processi biologici. Del fenomeno se ne è discusso a Seattle, nel corso del convegno annuale della Geological Society of America. Ora gli studiosi cercheranno di capire perché i meteoriti analizzati presentano solo determinati amminoacidi, mentre mancano di tutti gli altri.

Meteoroid Bombardment May Have Made Earth More Habitable, Says Study

When a meteoroid from space enters a planet’s atmosphere, extreme heat causes some of the minerals and organic matter on its outer crust to be released as water and carbon dioxide (as a meteor burning up in the atmosphere) before it breaks up and hits the ground (and becomes a meteorite). Researchers suggest the delivery of this water could have made Earth’s and Mars’ atmospheres wetter. The release of the greenhouse gas carbon dioxide could have trapped more energy from sunlight to make Earth and Mars warm enough to sustain liquid oceans. In the new study, researchers from Imperial College London analysed the remaining mineral and organic content of fifteen fragments of ancient meteorites that had crashed around the world to see how much water vapour and carbon dioxide they would release when subjected to very high temperatures like those that they would experience upon entering the Earth’s atmosphere. The researchers used a new technique called pyrolysis-FTIR, which uses electricity to rapidly heat the fragments at a rate of 20,000 degrees Celsius per second, and they then measured the gases released. They found that on average, each meteorite was capable of releasing up to 12 percent of the object's mass as water vapour and 6 percent of its mass as carbon dioxide when entering an atmosphere. They concluded that contributions from individual meteorites were small and were unlikely to have a significant impact on the atmospheres of planets on their own. The researchers then analysed data from an ancient meteor shower called the Late Heavy Bombardment (LHB), which occurred 4 billion years ago, where millions of rocks crashed to Earth and Mars over a period of 20 million years. Using published models of meteoritic impact rates during the LHB, the researchers calculated that 10 billion tonnes of carbon dioxide and 10 billion tonnes of water vapour could have been delivered to the atmospheres of Earth and Mars each year. This suggests that the LHB could have delivered enough carbon dioxide and water vapour to turn the atmospheres of the two planets into warmer and wetter environments that were more habitable for life, say the researchers.

(Science Daily)