Human activity is causing one of the largest mass extinction of species the world has ever seen, according to a new study conducted by scientists in Mexico.

An international team of researchers led by the National Autonomous University (UNAM) has found that since the year 1900, about 477 different species have become extinct because of continued human degradation and destruction of natural habitats.

The team, led by UNAM researcher Gerardo Ceballos, calculated for the natural rate of extinction that has occurred in previous years through the use of fossil records. They then compared this figure to the one they observed in the past 100 years.

They found that for every 10,000 species in the world, about two of them die off every century.

In the past 100 years alone, however, about 500 species have become extinct instead of the nine species that would have been expected at natural rates.

These extinct species include 158 fish, 146 amphibians, 80 birds, 69 mammals and 24 reptiles. The researchers said these estimates are highly conservative at best.

While such a study is susceptible to overestimation of modern-day extinction rates, especially given the limited data available, the researchers placed a floor on their figures so that the conservative extinction rates they arrived at would not be any lower given the data they had.

This means their findings are much more significant because even with the conservative estimates, they were able to calculate for extinction rates that are much higher compared to the background extinction rate, or the rate at which species are lost without any human impact involved.

Earlier studies have tried to establish the background rate of extinction for species. The results produced upper values of around one in every one million species lost every year.

The UNAM-led team used previous work made by co-author Anthony Barnosky in calculating for the background extinction rate, effectively doubling the first established rate. They assumed that two out of every one million species will become extinct through natural causes every year.

The researchers expected the differences between the background extinction rates and the human-caused extinction rates to shrink, but they discovered that the importance of more recent die offs is so overwhelming that it overrode any naturally-occurring processes.

The conservative estimate of the loss of species follows data collected from the International Union of Conservation of Nature. This includes recorded samples of several species becoming extinct.

The researchers made use of the same source of data to come up with their conservative estimate, which features identified extinct species and those considered to have died off or extinct while in the wild.

The National Autonomous University-led study is published in the journal Science Advances, and it includes a list of vertebrate species that have become extinct since 1500.

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