This statement in the article I find important, it seems to be passed over in various popular reports to the public and glad to see this here.
"Other research suggests that the Red Planet may have once been white, an icy wasteland with an average temperature of minus 54 degrees F (minus 48 degrees C). According to Robin Wordsworth, a researcher at Harvard, a colder scenario is more straightforward to model because Mars only gets 43 percent of the solar energy of Earth, and early Mars was lit by a younger sun believed to have been 25 percent dimmer than it is today. "That makes it very likely early Mars was cold and icy," he said in a statement."
This is the Faint Young Sun and different models indicate the ZAMS Sun produced perhaps 40% less energy than today some 4.5 billion years ago. Some models indicate 3.5 billion years ago for Earth, the Faint Young Sun emitted about 25% less solar energy so the average temperature of Earth could be -2C, Mars even colder and 4 billion years ago, colder still. Using the H-R star diagram, the ZAMS Sun is located in a different position than the present Sun where life abounds on Earth today.