A significant breakthrough in the understanding of Earth's history has been made.

New analysis of ancient crystal grains embedded in rocks from the Australian outback suggests that Earth had land and fresh water about a billion years ago - a time when scientists thought the planet was completely covered by ocean.

A study published in Nature Geoscience provides the first evidence of fresh water and land on Earth four billion years ago.

The oldest preserved crystals date back more than four billion years. A number of ancient crystals come from the Jack Hills in the Midwest of Western Australia.

Chemical clues contained in zircon crystals have shown that the hot molten rock in which they formed came into contact with fresh water during crystal formation.

Ten percent of all crystals analyzed were older than four billion years.

The study's lead author, Hamed Gamaleldien, told the Express that "state-of-the-art techniques were used in Curtin and China to determine the age and oxygen isotopes of these zircon grains" and that their discovery is "important for the evolution of life".

"Zircon is the only mineral whose age we can determine with certainty; most other dateable minerals are likely to have lost their original characteristics through later grain-altering processes," he said.

"And other stable grains like quartz can't be dated because they don't have radioactive elements that can give us an age."

"We measured the ratio of heavy oxygen to light oxygen, which is thought to be much lighter in fresh water than in seawater."

The discovery has far-reaching implications for our understanding of Earth's early history and the potential for life.