It has been inferred from the probable number of languages and the estimate of pre-contact population levels that there may have been from 3,000 to 4,000 speakers on average for each of the 250 languages. A number of these languages were almost immediately wiped out within decades of colonisation, the case of the Aboriginal Tasmanians being one notorious example of precipitous linguistic ethnocide. Tasmania had been separated from the mainland at the end of the Quaternary glaciation, and Indigenous Tasmanians remained isolated from the outside world for around 12,000 years. Claire Bowern has concluded in a recent study that there were twelve Tasmanian languages, and that those languages are unrelated (that is, not demonstrably related) to those on the Australian mainland.