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Speculation has come and gone as to when the world will end, but now scientists have put a date to when Earth will become unable to host life. Rest assured though, that day will only come some 1.75 billion years from now.

Researchers at the University of East Anglia in the United Kingdom have determined that Earth will become inhabitable in 1.75 billion to 3.25 billion years' time. However, scientists estimate that before this time, astronomical forces will eventually render the planet uninhabitable. Somewhere between 1.75 billion and 3.25 billion years from now, Earth will travel out of the solar system's habitable zone and into the "hot zone," new research indicates.

"It will get progressively hotter and there's nothing we can do about it," said Andrew Rushby, who studies planet habitability at the University of East Anglia.

The scientists' work is based on the concept of habitable zones - the "Goldilocks regions" of space around stars where the surface of a planet is neither too hot nor too cold for that essential for life, liquid water, to flow, according to the research published Sept. 18 in the journal Astrobiology.

The researchers looked at the origin of life in order to determine how much long the Earth will be able to sustain life. Simple cells first appeared on Earth nearly 4 billion years ago. "We had insects 400 million years ago, dinosaurs 300 million years ago and flowering plants 130 million years ago," lead researcher Andrew Rushby, of the University of East Anglia in the United Kingdom, said in a statement."Anatomically modern humans have only been around for the last 200,000 years - so you can see it takes a really long time for intelligent life to develop."

The researchers created a new tool to help evaluate the amount of time available for the evolution of life on other planets: a model that predicts the time a planet would spend in its habitable zone. They then applied the model to Earth and eight other planets currently in the habitable zone, including Mars. 

They calculated that Earth's habitable-zone lifetime is as long as 7.79 billion years. (Earth is estimated to be about 4.5 billion years old.) Meanwhile, the other planets had habitable-zone lifetimes ranging from 1 billion years to 54.72 billion years.