FORBES - Carbon Dioxide is often vilified as a bugaboo greenhouse gas. But its presence here on early earth is likely one of the reasons we are here to talk about it. Carbon dioxide, or CO2, was likely needed in large quantities in earth’s early atmosphere to raise temperatures sufficiently to enable the onset of the earliest microbial life. That’s because some four billion years ago, our sun had only about 70 percent of its current luminosity.
But there’s a catch. CO2 in large quantities can also be deleterious to the evolution of complex life —- particularly intelligent life like our own. We wouldn’t be here at all if our earth hadn’t developed a means of ridding its atmosphere of large quantities of CO2 via carbon recycling. That’s the process by which carbon in our atmosphere is subducted below earth’s surface in a process facilitated by the movement of giant tectonic plates below earth’s outermost crust.
Terrestrial mass planets around other sunlike stars may not be so lucky and may have long held onto their CO2-rich atmospheres. That’s not too much of a problem for microbial life. But it could be one of the factors that narrows the range of planets that could host intelligent life like ours.
Humans breathe O2 and exhale CO2, which is a waste product, Eddie Schwieterman, an astrobiologist at the University of California, Riverside, told me at the ‘Unique Species on a Unique Planet?’ astrobiology confererence in Copenhagen. We require abundant oxygen to survive, but CO2 levels which are too high poison us, he says. So, we could not have originated in an environment that would preclude our survival, so we should not be surprised that we find ourselves in a high-O2, low-CO2 world, says Schwieterman.