The world's native languages are dying out at an unprecedented rate, taking with them irreplaceable knowledge about the natural world, according to a National Geographic study.
The study identified five global "hot spots" where languages are vanishing faster than anywhere else -- eastern Siberia, northern Australia, central South America, the US state of Oklahoma and the US Pacific Northwest.
"Languages are undergoing a global extinction crisis that greatly exceeds the pace of species extinction," linguistics professor David Harrison told the National Geographic website (www.nationalgeographic.com).
Harrison said half of the world's 7,000 languages were expected to disappear before the end of the century.
He said indigenous people had an intimate knowledge of their environment that was lost when their language disappeared, along with concepts dealing with mathematics and the nature of time often unfamiliar to western thinking.
"Most of what we know about species and ecosystems is not written down anywhere, it's only in people's heads," he said.
"We are seeing in front of our eyes the erosion of the human knowledge base."
Harrison was one of a team of linguists who carried out the study released Tuesday.
The researchers travelled to Australia this year to study Aboriginal languages, some of the most endangered.
"Australia is amazing because humans have been there for 50,000 years and they represent an unbroken link to the past in a way that other places on Earth don't," Harrison said.
"You can really glimpse human prehistory and the mythological beliefs and systems that they have produced and passed on orally with absolutely no recourse to writing of any kind."
While in Australia they found a man with knowledge of the Amurdag language, which had previously been thought exctinct.
The researchers said all five of the hot spots identified were areas that had been successfully colonised and where a dominant language such as Spanish or English was threatening native tongues.
Harrison said that in Australia, they were heartened to see a woman in her 80s who was one of only three remaining speakers of the Yawuru language passing on her knowledge to schoolchildren.
He said such inter-generational exchanges were the only way native languages could survive.
"The children had elected to take this course, no one forced them," he said.
"When we asked them why they were learning it, they said, 'This is a dying language, we need to learn it'."