JWST M51 image credit: ESA/Webb, NASA & CSA, A. Adamo (Stockholm University) and the FEAST JWST team

I’ve written another OpEd for Scientific American, this time about what evidence we have for UFOs (or, in the modern tongue, UAPs for Unidentified Anomalous Phenomena). You can guess where I stand here; despite a lot of sound and fury the current evidence signifies nothing. I also talk a bit about astronomer Avi Loeb, who has made a lot of claims about natural phenomena being possibly due to alien spaceships, which, again as you can imagine, I take a pretty dim view of.

I’ve bumped heads with UFOers many times over the years. Most of the time their claims are laughable (Stanton Friedman was a loud voice about this for decades, and he, um, was not a fan of mine), and —as is usual for anti-science claims — it can be difficult to distinguish between true believers and grifters.

But given that, a lot of UFO enthusiasts have (usually sarcastically) asked me what evidence would it take to convince me alien visitation are real. One landing on the White House lawn?

My answer is an immediate: Yes! Exactly! That’s the sort of standard we should be seeking here. Not blurry photos or shaky evidence or straight-up assertions, no matter how vigorously made.

And even with Klaatu setting his flying saucer down in central DC I’d still want more. I’d ask the occupants if they have knowledge of something we don’t or cannot know but could later determine. Where’s Planet Nine in the sky? Describe all the planets orbiting Proxima Centauri. What supernova’s light will reach Earth next? Can they provide a sample of an element we haven’t yet seen on Earth?

Look: I’m an astronomer. As a profession, there’s no one on Earth who wants alien visitations to be real more than we do. We spend our lives dedicated to studying objects we can never visit, never touch, and hardly even see. Most of us would drop everything, instantly, for the chance to actually go and visit them in person and see them up close^*. Yet—with few exceptions—we are among the most skeptical of these very claims.

Why? Because we don’t want to believe. We want to know.

 ^* I mean, I wrote a whole book about this.

The Great Oxygenation Event, or GOE, was one of the largest events in Earth’s history, possibly the first mass extinction event, and I’d argue the biggest climate event. Before about 2.5 billion years ago, the Earth’s atmosphere had no free oxygen in it. It was all locked up in rocks and water. But then something happened, and suddenly, geologically speaking, the amount of oxygen in Earth’s air climbed rapidly.

The culprit is almost certainly cyanobacteria. These relatively simple microorganisms evolved the ability to convert sunshine into energy they can use, and released oxygen as a waste product. Over time it built up, killing off a lot of anaerobic bacteria (ones that didn’t use oxygen) at the time. Eventually some evolved the ability to use oxygen, which is like supercharging your metabolism; when oxygen combines with other elements you can extract a lot of energy out of the reactions. Those organisms were able to outcompete anaerobic ones, and the rest is (very very ancient) history. 

Or is it? We don’t know a lot of details about the GOE. Did it happen all at once, or in spurts? How long did it really take?

New research indicates it happened over time, in fits and starts. Atmospheric oxygen levels went up, then down, then up again, likely many times before reaching some critical point and just rising [link to journal paper].

The researchers figured this out using a proxy, some reaction depends on oxygen to work, so they didn’t need to measure oxygen directly. They analyzed the presence of a sulfur compound in shale sediments known to form only when there’s no oxygen present, and found the amount of this material in shale rose and fell many times just before the GOE, indicating atmospheric oxygen levels fluctuated.

But there’s more. Life was in the ocean at the time — it hadn’t evolved to live on land yet, as far as we know — so they also looked for proxies in those shales that were made in water. That meant thallium isotopes, the abundance of which are sensitive to the presence of manganese oxide in the seafloor, and found the same pattern corresponding to the sulfur compounds in the same shales. Manganese oxide would be more abundant when there was more oxygen in the water for manganese to combine with, so thallium is another proxy for oxygen levels.

Details aside, what they found is it looks like the GOE took over 200 million years to fully play out, which is a long time. And even then it was not constant. That doesn’t surprise me much; at first the oxygen would have been absorbed by minerals, for example, so at the very beginning the levels would’ve fluctuated a lot, especially given volcanic activity. But eventually it got its act together, and reached levels similar to what we see today, about 21% (the major component of our air is nitrogen at 78%, with various other gases making up the rest). That level still goes up and down — in some prehistoric times there were higher levels, which is likely why insects could grow bigger during the Carboniferous and Permian periods, with some dragonflies having 60-cm wingspans!

We owe our existence to little bacteria that lived and died billions of years ago. They poisoned the planet, as far as most life at the time was concerned. As I point out in my article on The Old Blog™, I hope we can get our own act together quickly enough that we don’t do the same.

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