A scientist in India has discovered a fossilised version of the earliest form of life, preserved for a mind-blowing two billion years.

Geologist Naresh Ghose found the prokaryote, a tiny, single celled organism, in shale underlying volcanic rock in the Gwalior basin of the Bundelkhand region near Jhansi.

He announced the find – the first of its kind – at the recent annual convention of the Indian Geological Congress in Nagpur.

"The present study reports for the first time the presence of "organogenic" microfossils – derived from living organisms," Ghose told the conference, according to the New Indian Express.

"Therefore, the microfossils [Prokaryotic-RNA cell] in the Gwalior basin may be regarded as the confirmed oldest existence of life dated about 2,000 million years ago ever to be recorded from the Indian subcontinent," he added.

"This important discovery was made using a simple and inexpensive device like a microscope without the aid of any sophisticated instrument," he said.

Prokaryotes are bacteria, usually single-celled, and without a nucleus. They were the world's only life form for most of its history, Jere H. Lipps, Director of the UCAL Museum of Paleontology, explains on the museum's website.

They first came into existence around three and a half billion years ago. It is not clear how they evolved into more complex forms of life. Prokaryotes have been found in rocks as old as three billion years.

Earlier this year, scientists discovered 1.6 billion-year-old eukaryotes in central India but Ghose's find is even older. He used his presentation at the convention to encourage citizen scientists to explore the natural world.

He said: "This important discovery was made using a simple and inexpensive device like a microscope without the aid of any sophisticated instrument."