Mayans were wiped out by drought

Despite a Mayan prophecy, the world did not end on December 21 last year - but new evidence suggests the ancient civilisation's calendar system was, in other respects, accurate.
By re-analysing a wooden beam from a Guatemalan temple, originally radiocarbon-tested in 1960, scientists believe it shows the Maya culture did collapse a thousand years ago because it failed to cope with climate change - a proposition first suggested last year.
The Central American people had developed a sophisticated society, accurate calendars and complex architecture including pyramids.
They thrived during rainy periods but a prolonged drought somewhere between AD 800 and 1100 is said to have brought about its collapse.
For a long time, experts struggled to match dates from the Mayan Long Count calendar with the modern European calendar.
The Long Count system comprised 20-day cycles made up of k'in, which formed 360-day cycles known as tuns.
Another unit, b'ak'tun, represented a cycle of 400 years - and it was the ending of one of these that led to the belief of the apocalypse in 2012.
Now, archaeologist Douglas Kennett, from Pennsylvania State University, has applied modern carbon dating methods to a lintel, carved with historical records, found at Tikal, which was a major Mayan city, according to NBC News.
His aim was to confirm the accuracy of the dating: 50 years ago, other researchers at the university reckoned the beam had been carved between AD 695 and 712.
"When looking at how climate affects the rise and fall of the Maya, I began to question how accurately the two calendars correlated using those methods," Kennett said.
As well as using carbon isotopes to establish its age, he and his team looked at the tree rings in the wood.
The date they concluded was around AD 658-696, which backed up the original correlation estimates.
The two estimates match up even more closely after factoring in the removal of ten to 15 years of wood growth while the carving took place, the researchers said in the journal Scientific Reports.
The lintel they analysed concerned the defeat of Tick'aak K'ahk', king of the nearby city of Calakmul, by Tikal's leader Jasaw Chan K'awiil.
This is turned re-confirmed the theory that the victory was in AD 695, 13 years after Jasaw Chan K'awiil took to the throne.
Their report in the journal continued: "These events and those recorded at cities throughout the Maya lowlands can now be harmonized with greater assurance to other environmental, climatic and archaeological datasets."