Oxygen and the banded iron formation shown above are just two of an endless number of fascinating manifestations of physics and chemistry that span time and space, from super nova to the intertwined web of life on an ancient earth to the the rise and fall of human empire. But fair warning, if you go below the fold today, there's going to be a surprise twist at the end of that story. One that may test the compassion and respect you're willing to show for your fellow progressive.
There is evidence photosynthetic oxygen production has been around for more than three billion years. But it really came into its own about two billion years ago. If you could visit the earth during the start of the Paleoproterozoic Era you would be hard pressed to recognize it! The earth was warmer then despite the sun being cooler, the moon was roughly two-thirds as far away as it is now; it would have been huge and beautiful in the sky. Sadly, there would have been little time to marvel at the alien earth without a spacesuit of some sort to keep you breathing. But free oxygen was in the mail and it would change everything.
Photosynthesis had arrived on the primeval earth, little cells were bubbling the stuff off like soda water, some of them were busy being incorporated into larger collectives, the forerunners of prokaryotes and eukaryotes, which would one day become part and parcel to plants and animals respectively. As the oxygen content of the early oceans grew, it reacted like oxygen does, with anything it could. Oxygen reacted with dissolved iron in the seawater and settled out in vast deposits called banded iron formations. Much of the iron and alloys like steel are possible today because of this process. For this and other reasons we may think highly of oxygen today—after all it's good for the brain!—but back then it was a deadly new poison. There is a school of thought that whole microbial ecologies crashed and died under the new chemical assault called the Oxygen Catastrophe.
As oxygen producing cells rose they consumed carbon dioxide, a potent greenhouse gas, earth lost one its warm blankets. The result was a period of ice ages, some so brutal they may have covered the entire world. If not for greenhouse gases released by volcanoes that periodically built up in the absence of traditional storm systems, we might never have emerged from this snowball earth. But emerge we did, and by the Cambrian, beginning about 550 MYA, life had grown complex, plants and animals now danced in resonance with predators and prey, the first modern marine biome developed. Oxygen became so concentrated in the air some of it lofted all the way to the stratosphere, where it formed a UV filter composed of ozone without which life may never have gained a robust foothold on land.
Ozone is made of pure oxygen, and yet it's radically different from the oxygen you breathe, it has a different number of individual oxygen atoms. A compound made of the same element but with a different number of atoms in the molecule is called an allotrope. Whereas diatomic oxygen, written O2, is good for the brain, three oxygen atoms forming ozone or O3 is a deadly poison for humans. That may sound counter-intuitive, but oxygen is not the only such good versus bad allotrope you've probably heard about. Remember the movie Erin Brokovich and her nemesis Pacific Gas & Electric? At issue there was the effect of two different kinds of chromium. There are benign allotropes of chromium, one so safe you can buy it in the health food store and add to your food. But the kind Brokovich found used by PG & E was hexavalent chromium, a deadly form. The only chemical difference between the two is a few chromium atoms (Actually, just a few electrons in the outer shell -- DS).
Allotropes aren't the only example of the difference an atom can make, the vast majority of chemical compounds includes two or more elements and we see the same sort of dramatic change there, too. Sodium is toxic and caustic, pure chlorine is deadly. But combine them and they form Sodium Chloride. If that sounds familiar it should, it's table salt, absolutely essential for life.
The point of this is two-fold: one, it's fascinating stuff! But two, just because an element is bad for humans in one form does not mean it is bad in another, far from it. And that's where another element comes in, one named after the fleet-footed god in Roman mythology: Mercury.
Ever hear the phrase "mad as a hatter"? In the 19th century mercury was used in the production of materials used to make clothing. Tailors that made their own felt or who were exposed to gads of the fresh stuff over long periods of time could suffer the consequences. Among them loss of memory, emotion, and other basic cognitive functions. So it's not surprising that substances containing mercury are highly regulated and are suspect in all kinds of neurological disease. Since autism is usually diagnosed around the same time childhood vaccinations are given, it's completely appropriate that vaccines containing a compound of mercury called thimerosal have been scrutinized for links to that condition.
But to date, no such links have been established. Just to be safe, almost all drug makers stopped using thimerasol over a decade ago, but rates of childhood autism remained unabated, adding to the idea that there is no demonstrable cause and effect. Most researchers concerned with the condition then begin looking elsewhere for a solution to the mystery. But some folks had become invested in thimerasol, some had even come to make living off the fear of mercury in vaccines, and some of those have proven less scrupulous than others. A whole cadre of charlatans have arisen who exploit parents' worst fears for personal reasons—mostly for profit. Despite being exposed again and again as unreliable, in some cases dramatically, good people have been taken in, whether by skilled operators or concerned citizens with good intentions is a judgement you'll have to make.
For those of us in the progressive science blogging community, pushing back against antivaxxars, as they've come to be called, is not just a matter of principle or preserving some hare-brained idea of false equivalency; if a few people listen to these guys it is potentially disastrous for all. Per usual the people who will pay first are the sick, the poor, the young, the weak, and the old. That's because diseases like smallpox, typhus, flu, etc., used to kill more people than just about everything else combined, they tend to zero in on the most vulnerable, and that horseman can ride again!
One big reason this panoply of diseases do not exact such a tragic toll anymore is because of vaccinations. That could change in just a few short years if a critical fraction of parents in a given region become so fearful of vaccination that they withhold them from their children: just as climate change poses a risk in part because a few influential people have become invested in denying it, what might be called an nascent anti-vaccination movement poses a risk. It is my hope we can persuade those who are concerned that that skepticism is currently unwarranted. More importantly, to develop better treatment, we need to know more, a lot more, about the exact underlying causes of childhood autism.