A new study published in the Geophysical Research Letters journal last week reveals that sand ripples, dunes, and rocks on Mars indicate the ancient red planet once held many similarities to Earth, reported The Washington Post. Conducted by researchers at the Los Alamos National Laboratory in New Mexico, the study findings show that planet Mars around 4 billion years ago would have looked much more like Earth to us than it does today.

“A vast shallow sea shimmered beneath oxygen-rich skies. The rocky crests of cliffs and hills reflected in the still water below. The landscape would have been familiar, except for its eerie desolation; nothing on the entire planet moved but the sands shifting in the wind.”

This vision is one developed by researcher Nina Lanza and her colleagues, who argue that the recent discovery of manganese oxide on the surface of Mars – a substance that can only form in a wet, oxygen-rich environment – shows that the planet was once much more similar to Earth than it is now. Today, Mars is a frozen, barren wasteland that is characterized mainly by ancient, muted red-hued rock that has been twisted into a wide variety of peculiar formations and ripples over time.

Another study published last week in the journal Science also delves into similarities to Earth in Mars’ ancient past, this time involving strange ripples in the sand that forms only in the thin, arid atmosphere of the red planet. This fossilized formation is estimated to date back more than 3.7 billion years and – along with the New Mexico study – highlights an important and little-known period in the history of Mars, when the planet began to lose its atmosphere and with it, the ability to hold onto liquid water.

“The formations are fluid drag ripples, similar to those seen underwater in stream beds on Earth, and their size is controlled by the thickness of the Martian atmosphere.”

Researchers reportedly discovered the pattern in sand on Mars when the NASA rover Curiosity stopped at a set of dunes in the planet’s Gale crater during late 2015 and early 2016. The current research suggests that the if the ripples on Mars are indeed simply patterns that were preserved in the sand as it turned to stone, they could serve as a sort of “paleo-barometer.”

“The scientists found ripple patterns in ancient rocks that are slightly smaller than the ones found across the planet today,” wrote Sciencemag.org. “That, they say, suggests that the ancient atmosphere was slightly thicker.”

According to the science team behind the Curiosity mission, planets Earth and Mars both have large and small sand dunes, with ripples of similar sizes, but Mars also has ripples that are in between – about three meters – and are not found on Earth. Curiosity conducted the world’s first up-close study of active sand dunes not on planet Earth six months ago when it explored the Bagnold Dunes on the northwestern slope of Mount Sharp on Mars.

Learn more about sand dunes on planet Mars:

“Both planets have true dunes – typically larger than a football field – with downwind faces shaped by sand avalanches, making them steeper than the upwind faces,” wrote Science Daily.

As Curiosity approached the Bagnold Dunes on Mars, however, researchers were able to determine that the crest lines of the three-meter ripples are sinuous, like the sand ripples that form underwater on Earth. Additional findings from Curiosity’s work on Mars also show similarities to how dunes behave on planet Earth. Today, the rover is investigating evidence about how and when ancient environmental conditions in the area changed from freshwater settings favorable for microbial life into drier conditions that are less habitable.

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