Earth 'home to 8.7 million species'

Previous guesses had put the total number of different types of plant and animal on Earth at anywhere between three million and 100 million. Now, a new calculation, based on the way in which life forms are classified, puts the estimate at 8.7 million.

The list of known species currently stands at about 1.2 million, but scientists say that the remainder could be found and classified within the next century.

The research was undertaken by a team from the Census of Marine Life, a 10-year project involving 2,700 scientists from over 80 countries aimed at assessing the diversity of life in seas and oceans, 'The Daily Telegraph' reported.

By analysing the rate at which the more generic groups, such as mammals and fish, break down into smaller ones the scientists were able to predict the number of species at the lowest level despite not having found them yet.

When tested against well-known groups like mammals, birds and fish, the method accurately predicted the number of individual species, study leader Dr Camilo Mora was quoted by the British newspaper as saying.

The formula predicted there are 7.77 million species of animal, of which fewer than one million have been catalogued, 298,000 species of plants, and 611,000 species of fungi on the planet.

Dr Sina Adl, one of the scientists, added: "If we really want to understand how our environment works we need to have a sense of what the species in it are and how they interact. If we have been trying to manage the environment with only 10 per cent of its species known, then it is no surprise that we are not doing a very good job."

Most of the species which have been found are vertebrates, like mammals and birds, while many of the 7.5 million undiscovered species lurk in the seas and in the soil around us, according to the findings published in the 'Public Library of Science Biology' journal.

In a commentary accompanying the study, Robert May of Oxford University said: "My optimistic guess would be around a century to complete our assessment of the diversity of life on Earth."