Tales of the Heliosphere

Are the red rocks that dominate the Martian landscape evidence that Mars once had life? The answer is "yes," according to San Diego State geology professor Gary Peterson. Peterson dropped his bombshell conclusion on an audience of the San Diego Astronomy Association during his lecture, "The Great Martian Climate Change," on Wednesday.

Peterson turned to his lifetime of studying geology here on Earth to Mars to make his case. Peterson took as his bedrock (it's a pun, I know, live with it) three assumptions that all terrestrial planets in the solar system formed at the same time, the same way, and from the same materials, through a long process of asteroid and comet collisions. The differences among the terrestrial planets today are due to their different masses and distances from the sun, which have affected their evolution over time.

All things being equal Mars should be like Earth. But Earth's mass has enabled it to hold on to most gases during its long life and given us our present atmosphere dominated by nitrogen and oxygen. The lighter mass of Mars on the other hand has caused it to lose most of its atmosphere except for the heavy gas carbon dioxide, and has left it with less than one percent oxygen. It also means that the pressure of the red planet's atmosphere today is less than one percent that of Earth's. That lower pressure, and the red planet's farther distance from the Sun, causes Mars to have an average temperature well below zero.

But the planet's red face means that some time in its distant past, Mars must have had oxygen levels as high as Earth's today, tropical temperatures, flowing water, and a thick atmosphere. According to Peterson, that red face also means that life probably existed on Mars when the Earth-like conditions existed there.

Red rock is hematite, which is made when basalt oxidizes, which requires moisture and oxygen. Basalt only turns red during oxidation in tropical temperatures. In colder temperatures, basalt oxidizes into a darker rust color. But what about red rock in St. George, Utah? That's nowhere near the tropics now but Peterson pointed out that during the Triassic period the area that eventually became St. George was below 20 degree north latitude in the tropics.

Mars has red rock on a global scale, which means that for a long time in its distant past, Mars was a tropical planet.

As Peterson put it, basalt on Earth oxidizes into hematite "reluctantly" despite a level of atmospheric oxygen at 21 percent. At some time in its past, up to 40 percent of Earth's atmosphere was oxygen. The less than one percent level of oxygen on Mars today is not sufficient to have oxidized the planet on a global scale. Thus, at one time in its past, Mars had to have oxygen levels similar to Earth's.

How does an atmosphere get oxygen? According to Peterson, oxygen is created two ways, either by photochemical dissociation, when sunlight reacts with water vapor to free the oxygen. The other source is life's process of photosynthesis. The interaction of sunlight and water vapor does not create the amounts of atmospheric oxygen needed to enable basalt to oxidize into hematite. Here on Earth, our atmosphere contains only one percent oxygen created by sunlight and water vapor. Twenty percent of our atmosphere is oxygen created by photosynthesis, mostly from bacterial life.

Thus, Peterson concludes, for Mars to have rusted red on a global scale it must have had a high percentage of oxygen in its atmosphere at one time. Since photochemical dissociation doesn't create enough atmospheric oxygen to turn basalt to hematite over an entire planet, photosynthesis, probably from bacterial life, must have filled the Martian atmosphere with the oxygen that eventually turned Mars into the rusted red rock it is today.

After the formal talk, Peterson speculated that the atmospheric methane on Mars could come from long-dead Martian life in oil shale. Oil shale is formed on Earth from deposits of silt and organic debris on lakebeds and sea bottoms. Heat and pressure change the deposits into a stable mixture of inorganic minerals and solidified organic sludge, known as oil shale. (Click here for Wikipedia article.)
If Peterson's correct that there's shale oil in them thar former lake bed craters on Mars, the US has just the right president in office today to lead the way. Operation Martian Freedom, anybody?

-tdr

Labels: Mars