Martians are of Terrestrial ancestry: their earliest ancestors were native to Earth, but they developed an advanced civilization and eventually left Earth for Mars, all before our own species had advanced past the Stone Age. They genetically engineered themselves to survive in the Arean oceans. At that time, Mars did have dry land, but its powerful seasonal monsoons made the surface virtually uninhabitable.
Mars's ocean were much shallower than those of Earth even at their greatest depth, with an average of just 115 feet. They were also highly saline, but the salt in question was not sodium chloride, which is responsible for the salinity of Earth's oceans. Instead it was magnesium sulfate—a compound made of magnesium and sulfuric acid. While the radioactive elements in Mars's core did play a role in forming its electromagnetic field, like on Earth, part of that electromagnetic field was also generated by ocean circulation because of the high concentrations of magnesium sulfate.
This system eventually failed because the Martians, in attempting to create a habitable biosphere, introduced corals and marine algae from Earth such as Corallina and gorgonians. These organisms depleted the ocean's magnesium concentration as a part of their calcification process. Gradually at first, Mars's oceans were demineralized, and almost too gradually for the Martians to notice, the planet's electromagnetic field began to weaken as a result.
The weakening of the electromagnetic field enabled ultraviolet rays from the sun to strip the evaporated water from the planet's atmosphere. Mars's formerly violent monsoons grew less and less intense, a phenomenon which the Martians initially celebrated, until it became clear that the planet's oceans were also shrinking. And as the oceans dwindled in size and currents were disrupted, so their ability to generate an electromagnetic field deteriorated even more, forming a feedback loop which enabled water to be stripped away at faster and faster rates.
Eventually, the Martians were forced to genetically modify themselves yet again, this time for survival on an increasingly arid terrestrial world. The shift to dry land took place before the oceans vanished, as the concentrations of magnesium sulfate and other minerals left behind in the remaining water increased to inhospitable levels.
The planet's weakening electromagnetic field left the surface vulnerable to ultraviolet radiation. It was rapidly becoming too arid to be hospitable, surface temperatures were plummeting due to the loss of greenhouse gases, and the atmosphere's oxygen levels were also becoming depleted, rendering the air unbreathable. Before long the Martians gave up on surface life altogether and moved their civilization underground, where they remain to this day.
Martians first became aware of humans in the early 20th century, and began to anticipate possible contact with humans or human-directed drones after mankind successfully reached the moon. Some aspects of our technological development have baffled them, however, such as our use of radio waves to encode audible speech sounds instead of simply developing telepathy as they did.
Martians no longer possess the capacity for audible speech, either in an anatomic or neurological sense; they have fully adapted to telepathic communication and the association between telepathic "sounds" and the means by which those sounds would be produced anatomically has long since been forgotten. Instead, they have developed technology which may receive a telepathic signal and translate it into audible speech. Outwardly, it is not all that apparent that they aren't actually speaking, although some humans have described their vocal tone as sounding slightly odd.
The Martian Project is © G. K. Lancaster (2020-). No part of it may be used without permission.