If they were aliens to Earth, one of his first questions sure to be many different forms of life on this planet, and "we are ashamed of our response uncertainty," said Robert May, an eminent zoologist at the University of Oxford. Scientists tell the story of an international team that made the last estimate of the number of species on Earth. A total of 8.7 million species, 25% of them in the ocean might respond to these scientists, led by Camilo Mora, the aliens of May. Although they point out that the calculated error is above or below 1.3 million, a figure is considerably accurate, considering that so far stood the total number of species between three million and one hundred million. "If we do not know even the order of magnitude (one million, ten million, one hundred million ...) the number of inhabitants of a country, how can we plan ahead?" Raises, for example, a the authors of the research, Boris Worm (Dalhousie University, Canada). 86% of all terrestrial species and 91% of marine have not yet been discovered, described and cataloged, say Mora (Dalhousie University researcher, in Canada, and Hawaii, USA) and colleagues presented their technique for estimating species and the resulting data in the scientific journal PLoS Biology on the Internet. From that, 253 years ago, the Swedish scientist Carl Linnaeus [Unlink] created the system to name and describe species used so far, have cataloged more than 1.2 million (approximately one million 250,000 in land and oceans) and collected in general database, an estimated 700,000 more would be described and waiting to enter the database.The technique developed for this estimate is based on observation of the hierarchy of taxonomic categories, from the level of species and genera, orders and classes through to phyla and kingdoms, May said in an accompanying article in PLoS Biology also. Mora and his colleagues have found that for eukaryotes, the description of the higher taxonomic categories is much more complete than in the lower levels. Furthermore, analyzing the taxonomic groupings in the 1.2 million species currently in the Catalogue of Life and the World Register of Marine Species, number patterns have been found linking higher taxonomic levels to species. These patterns allow the estimates of number of species in lesser-known groups and get a total with a margin of error.The interest in knowing the number of species does not respond to mere scientific curiosity or the desire to look good in front of a hypothetical alien visiting Earth asking good questions. The question of the number of species on the planet, along with research into their distribution and abundance, "is particularly important now because a lot of human activities and impacts are accelerating the rate of extinctions, many species may disappear even before know we exist, we know your niche and role in ecosystems and that we can explore its potential contribution to improving human welfare, "said Mora in a statement the program Census of Marine Life.