How do scientists estimate the age of language?

Scientists have borrowed a technique from biology to calculate the age of our mother tongue. They say the Indo-European languages emerged more than 9,000 years ago. Languages evolve much as animals do, words gradually change over time just as gene evolves in the living beings. So a biologist in New Zealand decided to use the mathematical tools developed to estimate the age of living species to study the evolution of our mother tongue. He and a colleague studied 2,400 words in more than 80 so-called Indo-European languages. The researchers now report in Nature that these languages started out as a common tongue more than 9,000 years ago. That’s consistent with other research dating our root language. According to that hypothesis, Indo-Europeans started out in Anatolia, which is present-day Turkey, and spread through Europe as farmers settled the land.