In Real Life, Mars is the lifeless, dusty red planet next door to the lush, blue planet we call home, Earth. The implication that barren Mars once was as bountiful and full of life as Earth and has become a wasteland entirely through the activities of today's threat gives a chilling demonstration of what kind of potential damage could happen to our world. Often this sort of damage starts with Mars first and goes from the outside of the solar system to the interior.
Stories where Mars had a thriving civilization are getting to be a Discredited Trope these days due to real-life Martian probing finding little or no archeological evidence. The theorized reasons why Mars isn't thriving like Earth now has a lot to do with its significantly lower gravity being unable to hold in an atmosphere with enough air pressure to keep liquid water from evaporating away, or any ozone layer to protect it from deadly solar radiation; a slow environmental death of natural consequences. However, in the past before space probes, astronomers only had their telescopes and their imaginations pointed at Mars, giving plenty of room to think up entire alien civilizations living on it, or at the very least life.
This trope has its roots in a 19th Century theory that the planets were formed in reverse order to their proximity to the sun, gradually moving further from the source as they aged. Therefore, Mars was seen as an old, dried-up world whose best days were behind it. This same theory also gave rise to the trope of Venus as a youthful and fecund planet.
What is known about Mars that aligns with this trope is that flowing water almost certainly existed there on a grand scale early on in its history. Billions of years ago, when Mars's volcanism still flourished, areas of liquid water spanned the soon-to-be-Red Planet's surface, carving out features such as lakes, rivers and deltas. Recent studies have even found evidence that Mars still has some standing water on it, though not on the surface; below the crust around Mars's south polar ice caps — composed largely of carbon dioxide and water ice — is a system of subterranean lakes containing salty water. While one prominent theory argues that Mars’s water evaporated into space, analysis of Martian rocks has suggested that the majority of Mars's water is actually still on Mars, but has been sequestered into the planet's rocks and crust, contained within hydrated minerals over the ensuing aeons. The presence on Mars of certain minerals that outright require water to be present to form, such as opals (a hydrated amorphous form of silica) certainly lend credence to this idea.
In any case, Mars's surface is extremely dry, and though water does occasionally flow on its surface, dripping down from the ice caps and existing in thin films condensed out of the water vapour in the atmosphere, only the most extremophilic organisms would be able to stand a chance of survival here.
For other tropes relating to the changing view of our planetary neighbors, see Venus Is Wet and Strolling on Jupiter. Unlike the former trope, however, there is a hint of Truth in Television here. Astronomers really do believe that Mars may have, at the very least, possessed liquid water in the distant past, and this has in turn fueled discussion of whether the planet may have once had life.
- In The E.Y.E.S. of Mars, human civilization has mostly destroyed Mars' once lush ecosystem.
- Bad Planet shows Mars teeming with life before the arrival of the death-spiders that harvested all life on their world and reduced it into a designated "bad planet".
- In Warlord of Mars, Mars is depicted as once having massive oceans and the greatest superpower at the time being the seafaring empire of the White Martians, but a disaster led to the oceans drying up and the atmosphere being slowly destroyed.
- Dan Dare: In The Red Moon Mystery, it is shown that a thriving civilisation once existed on Mars: Dan's Uncle Ivor is an archaeologist who specialises in Martian ruins. Ivor discovers that Martian civilisation was destroyed by something called The Red Moon, just in time for said object to return and threaten Earth. Clues left by the last Emperor of Mars enable Earth to be saved and the Emperor to get his posthumous revenge.
- Last Child of Krypton: As it turns out, Mars was destroyed by the Angels instead of the White Martians.
- In chapter 46 of Mutant Histeria, the Acolytes, on the verge of their time-travelling journey, end up on Mars 3.6 billion years ago, and find it with a breathable atmosphere and oceans maintained by a civilization of ammonia/methane-based slime who are capable of spaceflight and even reading Sabertooth's brain to learn their language. This all comes apart when Sabertooth and Gambit's brawl knocks Pyro out and causes him to drop a fireball on one of the blobs, which then reaches their creeks and causes the entire civilization to literally burn out.
- Ice Age: Collision Course reveals that Mars was indeed wet and green and on the verge of birthing life. However, as the first amphibian crawls out of the water, it gets accidentally destroyed along with the rest of the planet by a Flying Saucer piloted by a mad squirrel with an acorn obsession.
- Ghidorah, the Three-Headed Monster states that Martian civilization was wiped out by the titular monster (this only applies to the English dub; in the Japanese version, it was Venus that was destroyed).
- In John Carter, it's said that Mars is dying out due to the actions of the Therns, and after the Therns are done with Mars they'll just move on to Earth. This doesn't happen in the book; in the book Mars is dying on its own and the natives have multiple methods in place to slow down the process. While the Therns' leader, Matai Shang, is a villain in the books, the filmmakers wanted him to be the villain of what was supposed to be a big franchise, so they needed to increase the plot stakes of his already-considerable evil.
- In Life (2017), a group of astronauts in the ISS discover a life form that annihilated all life on Mars and now wants visit Earth.
- Near the end of Mission to Mars, the astronauts discover an ancient Martian orrery that explains that Mars was once very Earthlike and had spacefaring intelligent life on it. The planet suffered a cataclysm, and the Martians abandoned their homeworld and seeded Earth with life on their way out of the Solar System.
- In Quatermass and the Pit (U.S. title, Five Million Years to Earth), Professor Quatermass theorizes that a discovered spacecraft, with corpses of insectoid-beings within, originated from the now "dead" planet Mars, five million years ago when... "Mars must have been teeming with life," and even been highly advanced scientifically. But, the Martians "...realized their planet was doomed," and sought to preserve what they could of themselves by establishing a "colony by proxy" on Earth.
- In Species II, a disgraced scientist claims that Mars was once a thriving planet a billion years ago before the antagonistic aliens wrecked the entire ecosystem and are now trying to do the same thing to Earth. He was locked up to keep him quiet.
- Total Recall (1990) shows that Mars was once inhabited by ancients, who had a massive machine that maintained a breathable atmosphere and biosphere on the planet — which is now being uncovered by the mining operations going on in the movie's present.
- In Sergey Sukhinov's The 21st Century Chronicles series, it's eventually revealed that not only was Mars once habitable, but the Martians were a thriving, space-faring civilization. They had tech like Deflector Shields, powerful weapons, and devices for reconstructing past events by largely undetectable trace evidence. However, an even more advanced race arrived from another system and soundly defeated them, rendering Mars uninhabitable. Some of the survivors may have been taken as slaves, and others were forced to resettle to the neighboring planet, possibly becoming our ancestors.
- In the Animorphs book about the Ellimist, he first visits our solar system around the time the dinosaurs died out. He mentions that Mars has life, but it's dying and, unlike on Earth, isn't going to recover.
- A throwaway line in the first Jack Blank book shows that the planet of Mars once was as green as Earth, and that the reason it's as barren as it we know it is because the planet-consuming Rüstov already finished with it, and they are presently attempting to invade the Earth.
- In John Carter of Mars, Mars once had thriving seas and green life, but the planet is now on life support, with its great canals and even its atmosphere sustained artificially by its inhabitants who haven't given up the ghost. Its seas are so long gone that there are ancient ruins in the plains that used to be the bottom.
- The Long Mars: It's revealed that most iterations of Mars possessed ecosystems at some point that were ultimately destroyed when the planet cooled. On those few Marses that subsequently warmed up again due to volcanic activity, life is able to redevelop from spores and microscopic organisms buried underground... though, ultimately, there's only one Mars in three million where the native Martians were able to develop quickly enough to build a space elevator and get off-world before the planet cooled and died again.
- The Martian Chronicles shows a civilization living on Mars who didn't think Earthlings existed until they started landing on the planet, which the Martians attempt to resist as much as possible. Eventually, the Martians die off from a mild Earth disease and humans are all that remain on Mars.
- In Out of the Silent Planet, it turns out that Mars was once lushly habitable before being attacked and ravaged by the bent Oyarsa of Earth (i.e., Satan), and now life there is mostly limited to a few geothermal oases.
- One of Larry Niven Svetz stories, Rainbow Mars, involves time travel to Mars' verdant past, and chronicles what happened to it.
- The Sword Of Rhiannon: Present-day Mars is a desert planet (although the canals are water-filled) inhabited by Human Alien Martians, but a million years ago, Mars was much warmer, with extensive oceans.
- The War of the Worlds (1898) has the Martians invade the Earth because Mars is dying. They would go on to consume their solar system inward if they hadn't made their lifestyles so sterile that they can't survive an encounter from Earth's abundant microorganisms.
- Doctor Who: In the serial "Image of the Fendahl", the Doctor says the Fendahl were responsible for Mars becoming a dead planet.
- Kamen Rider Build: The first manned mission to Mars in 2007 discovered ruins and a mysterious object that researchers dubbed "Pandora's Box". Later in the series, it's revealed to be the work of a roving planet-destroying entity named Evolt, who used the Box to create an Unrealistic Black Hole that devastated the planet's surface — and he's seeking to do the same to Earth.
- Russian rap-rocker Noize MC has a song titled "На Марсе классно" (Na Marse klassno, "It's cool on Mars"), which claims that Mars used to have a thriving civilization not completely unlike Earth. Sadly, that civilization wiped itself out completely in a nuclear war.
- Rocket Age's Mars was once a cool, idyllic world, until some Ancient Martian scientists managed to knock their own planet out of its correct orbit by firing the Planet Killer Rocket at their enemies, turning Mars into a hot desert world.
- Space 1889 is set in an alternate Victorian era where Victorian science was correct about many things, including Mars. Mars was a fertile planet thousands of years ago but is now drying up and the great canals were an attempt to sustain it. Its people are remnants of a lost golden age, and Mars is now being colonized by the great European powers.
- Warhammer 40,000, set tens of thousands of years in the future, plays with this trope in a weird way. Mars was the first planet colonized by humanity, and it had been fully terraformed to be just like Terra (Earth), but that was Before the Dark Times. Eventually, the Age of Strife hit humanity, and the Martian atmospheric shields were shattered, turning the whole planet into a post-apocalyptic wasteland. People depended on technology to survive, hence why they turned to cybernetics. Eventually the planet was ruled by the Adeptus Mechanicus, a machine-worshiping cult that seek to implant themselves with cybernetics to 'transcend' humanity. As of the 41st millennium that Warhammer 40,000 is set in, Mars is a desertified Polluted Wasteland populated by technophile cultists and the people slaving away in their factories.
- Cognitive Dissonance has Mars dotted with wreckage and abandoned laboratories. The Data Logs detail that the Martians were leading a prosperous civilization, but it was ruined after a war with Jupiter caused by a misunderstanding, and another war in which they lost to Giegue, who then turned the remaining Martians into Starmen.
- In Crash Team Racing, a Dummied Out piece of dialogue from N. Oxide infers that he's responsible for this:
"You're the fastest racer so far? You're the best this planet can offer? This is going to be a bigger joke than that last civilization I challenged. What was it called... on that red planet so close to here... Oh, yes. I think you call it Mars. Now that was an easy win. What? You say there is no civilization on the planet Mars? (laughs) Not anymore! They lost the race!"
- In Cydonia: Mars - The First Manned Mission, the Martian people were once a peaceful race, until their strict caste system caused half the population to destroy the other using nuclear weapons, but another alien race left behind structures to help the survivors transcend reality. Since the human race has already decimated Earth, and you were sent to Mars in hopes of establishing a colony there, you have to follow this trail in search of the Ambassador that helped them. Using an alien UFO, you're able to warp back in time to when Mars was green, with a purple ocean and mushroom-like trees. When you gain the Ambassador's trust, it gives you the means to a new colony, where you can either lower an EMP field that lets mankind settle on Mars in its current, inhospitable state, or activate a device that terraforms Mars and turns it green again.
- Orthopox's exposition in the beginning of Destroy All Humans! states that when the Furons visited on Earth in ancient times to, err... relieve stress with early humans, they had just finished eradicating the Martians. Destroy All Humans! 2 elaborates that Mars used to be a full-on ocean world, until it was reduced to a barren wasteland by Furon weaponry. The main antagonists of the second game are lobster-like Martian remnants plotting to perform Hostile Terraforming on the Earth.
- Doom³: A civilization existed on Mars that was destroyed by The Legions of Hell, the exact same legions that are faced by the human space marine protagonist.
- In Ultima: Worlds of Adventure 2: Martian Dreams, the Avatar travels in time to the 19th century, and from there, to Mars, where a native civilization is discovered. Said civilization is in ruins, however, and the Avatar needs to help them with restoring Mars to a habitable state. Ultimately, Mars's environment cannot be saved. The Avatar is, however, able to place the minds of the surviving Martians into robots and re-locate them to Earth. Over the course of the next century or two, Mars's ecosystem dies completely, and the planet is reduced to the dusty, dry world we know today.
- In Waking Mars, it's theorized that Mars was indeed once green, except the lifeforms there were nothing like we're used to. The pseudoplants (called Zoa) you find and spread are recovering from a billion years of dormancy due to increased volcanic activity in the area. You eventually encounter the Sentients, native Martians, who are true Starfish Aliens. If you didn't know it, you could easily confuse them for yet another kind of Zoa. In the end, you can either have the Sentients revive Mars (which will only work for a few months) or escape the planet with you either staying aboard or going back to the Base Camp.
- Har Deshur: Visions of an alternate, slightly more habitable Mars is a Speculative Biology project whose basic premise is that, while it still deteriorated over time, Mars managed to stay slightly more habitable until modern day, allowing primitive plants and animals to carve out an existence, resembling Pre-Mariner-4 predictions.
- In the Ben 10: Alien Force episode "Fool's Gold", mischievous but harmless aliens come to a village every 17 years where they eat massive quantities of popcorn and defecate solid gold. When the town's mayor gets greedy and kidnaps one, he gives the alien a steak, causing the alien to grow into massive size and defecate unstable uranium. The alien's friend tells Ben that Mars "used to be called The Popcorn Planet" before his kind came there.
- Biker Mice from Mars managed to use the trope twice:
- The red planet is shown to have been a lush place before the Plutarkians invaded and literally stole away every resource, including the fertile soil.
- The 2006 revival shows that, before the Plutarkian invasion, the Martians themselves had ruined the ecosystem, but had repaired it with the Regenerator. The revival's Myth Arc deals with the attempt to recover the original Regenerator (now in the hands of Ronaldo Rump) or build a third one after the second one, who had apparently been used to restore Mars' resources after the Plutarkian's defeat, was destroyed before it could restore the water and fully revive the planet.
- Invader Zim: The Martians worked themselves into extinction converting their planet into a giant spaceship. Why? Because it was cool.
- The first arc of Justice League, "Secret Origins", displays an invasion of aliens coming to Earth. These aliens previously had taken Mars, leaving the Martian Manhunter as the Sole Survivor, who comes to Earth to warn the planet and help form the Justice League to fight them off.
- In Real Life, our probes have uncovered a lot of evidence indicating Mars once had oceans and running water, organic matter has been located by the "Curiosity" rover, and possible fossilized microbes have been found on meteorites in Antarctica traced back to the Martian crust. For its first billion years of existence perhaps, Mars might have had a magnetic field strong enough to sustain a decent atmosphere and protect a primitive biosphere — but being smaller and further from the Sun its core might have cooled fairly quickly, weakening that magnetic field to the point its atmosphere was (and still is being) stripped by the solar wind. There's also some evidence that a very massive object, possibly a dwarf planet like Ceres, impacted Mars in such a way as to throw the core itself off balance and likely disrupt its magnetism — the fact that the Southern Hemisphere crust is significantly thicker than the Northern is related to this.
- Another theory that plays into the idea that Mars was 'denied' a chance at being a planet filled with life plants the blame on Jupiter. Early on in the Solar System's history, Jupiter, the first of the planets to form around the Sun, formed much closer to the Sun than where it is now, and began rapidly migrating inward in what's referred to as the Grand tack hypothesis. On its journey towards the Sun and the infant rocky planets, Jupiter undertook a rampage of planetary proportions, slamming planets into each other or ejecting others into the Sun, while at the same time disrupting the accretion disks of Ceres and Mars, effectively stealing the rock and ice that was meant for them. Not only would this explain the considerably small sizes of the two (with Ceres being too small to apply the formal definition of a planet to it), but it could also explain Mars's lack of a magnetic field, as it was now too small to maintain one for as long as Earth. Earth could have very well met the same fate as Mars and Ceres, but fortunately the formation of Saturn and its subsequent 'capture' of Jupiter in an orbital resonance saved it from the King of the Planets' wrath.
- Inspiring some works of above, a theory that existed in the late nineteenth century and the very first part of the next one was that Mars was a dying world where Martians built an irrigation of canals from the polar caps to carry water to drier regions. Better observations showed both no canals and no water in Mars' atmosphere, and as noted at the beginning, spacecrafts sent there decades later finally shot it down.
- Another theory, that popped up when it was clear Mars lacked large bodies of liquid water, is that the dark spots (albedo features) that can be seen there with a telescope, formerly considered as seas, were areas of vegetation changing its extension as Martian seasons progressed. The late Carl Sagan suggested in the late '60s said dark areas were actually the result of dust being blown by the winds of Mars and that idea was vindicated when probes found exactly that.
- Leaving possible human-directed Terraforming aside, in a few billion years as the Sun's luminosity increases, Mars will have Earth-like temperatures. However this trope will very likely be averted, as it's too small and geologically inactive — change cold, dry and airless to hot, dry and airless as with no magnetic field to speak of and its low gravity, Mars' water would be lost to space — and in any case once the Sun goes full red giant, Mars will be a scorched, lava-covered Death World.
- Venus is also thought to have once had water (and possibly microbes) on it, until its own lack of a magnetic field caused the water to become disassociated by solar radiation, leaving nothing to prevent a runaway greenhouse effect that rendered the planet uninhabitable.