A recent study showed that Mars was warm and wet billions of years ago. The finding contrasts with another theory that this era was mainly cold and icy. The result has implications for the idea that life could have developed on the planet at this time.
Whether Mars was once habitable is a fascinating and intensely researched topic of interest over many decades. Mars, like the Earth, is about 4.5 billion years old and its geological history is divided into different epochs of time.
The latest paper relates to Mars during a time called the Noachian epoch, which extended from about 4.1 to 3.7 billion years ago. This was during a stage in solar system history called the Late Heavy Bombardment (LHB). Evidence for truly cataclysmic meteorite impacts during the LHB are found on many bodies throughout the solar system.
Two obvious scars from this era on Mars are the enormous Hellas and Argyre impact basins; both are well over a thousand miles across and each possesses enough volume to hold all the water in the Mediterranean with room to spare.
One might not imagine such a time being conducive to the existence of fragile lifeforms, yet it is likely to be the era in which Mars was most habitable. Evidence of landforms sculpted by water from this time is plentiful and include dried-up river valleys, lake beds, ancient coastlines and river deltas.
The prevailing climatic conditions of the Noachian are still a matter of intense debate. Two alternative scenarios are
typically posited: that this time was cold and icy, with occasional melting of large volumes of frozen water by meteorite impact and volcanic eruptions, or that it was warm, wet and largely ice-free.