Mike Tice

I have twisty ways of getting to my points! Sorry it was so convoluted.

I'll be giving a talk elsewhere during the BASE meeting, but Russell will be there representing our group. I'd be very happy to meet up with you remotely, too.

Definitely! There are many examples where individuals or groups have killed careers or held back good studies. It's bad for science and awful for scientists. My feeling, though, is that the scientific damage is mostly corrected by the scientific community, not politicians elevating dissenting views.

On a more fun note, here's a pretty X-ray image of a very old rock (3.22-billion-year-old Moodies sandstone from South Africa). Red=Fe, green=Ca, blue=Mn, white=Mn, cyan=K.

Respect for the scientific merits of a convincing study should extend to respect for the slow, multifaceted process that the community uses to evaluate and assimilate it. The hard-won agreement of people so prone to disagreement should mean a lot!

That's why I also believe that the huge variety of scientists' approaches should give weight to scientific consensus. If I disagree with the vast majority, my ideas should be taken seriously. But they shouldn't drive policy or education decisions under the guise of openness or an ideal science...

In the end, these personal differences (quirks?) between scientists constitute an important safeguard in evaluating any single study. My colleagues' idiosyncrasies help to keep my own oddities in check, even if the process can feel maddeningly slow or overly abrasive at times...

Scientists' starting positions generally already come from evidence and hard-won theory. Those positions generally shouldn't be abandoned or altered lightly. It can take time to absorb new approaches--it can be easier and safer to evaluate later evidence coming from a familiar direction...

It's now clear that my "realism" was rooted in cynicism as much as any real insight into how science works. "How could all of these scientists be so wedded to their ideas that they can't objectively evaluate new evidence?" I'm now more sympathetic about how slowly scientific opinions can shift...

I was asked as a graduate student if a paper I wrote was going to convince everyone about a conclusion that was controversial in the mid-2000s. Even as a newbie to my field, I wasn't naive enough to believe it would...

This is a beautiful figure! Even if this particular branch of research doesn't wind up in a publication soon, I hope your thinking on it informs other branches that are more immediately rewarding. That's how I've learned to make peace with my backlog!

You're right, but if these rocks were buried by other rocks or sediment and then heated for a long time, that could potentially do the trick. The temperature discussion in our paper argues against that possibility. We would be more sure with access to basic geologic tools in a lab on Earth, though.

Yes, at least things formed in similar ways. Keep following Perseverance to see what else might be around. However, we were lucky to find these. Rovers only get to closely examine a fraction of the rocks they encounter. These structures were only visible up close after the dust had been blown off.

@gsjphd.bsky.social is right: even animals that we think of as simple are incredibly complex. Paleontologists know a lot about how to recognize even old burrows in sedimentary rocks! The challenging things are small with geometric shapes (e.g., rods/spheres) more easily spoofed by other processes.

I'll be jumping up and down when we finally cross the threshold to certainty about life on other planets, either way. But I still think it's worth noticing when we've shrunk our own ignorance about an important question, and at least for now, this is one of those times.

The point is that it is not 1000:1 in either direction. And before finding these features, I would have told you that we didn't have enough information to distinguish between any of those possibilities. That, to me, is the exciting thing here...

All of this is to say, my gut feeling is that the poppy seeds and leopard spots stand about a 50:50 chance of holding up as solid evidence of life on ancient Mars. If you wanted to argue that the likelihood is closer to 20:80 or 80:20, I wouldn't disagree with you...

Finally, 5) is the potential biosignature corroborated by another independent sign of life?
*No extraterrestrial biosignature, including the leopard spots and poppy seeds, has yet crossed this threshold.*

If something unknown like that actually produced these Martian structures, we will have to learn about it through the concentrated research that will certainly follow from this paper...

I think it's a long shot for our interpretation to be wrong on this count. On the other hand, we can't completely discount the possibility of some unknown way for getting outside sulfide into these isolated spots, or for some exotic chemistry unknown in Earth sediments making sulfide in place...

4) How well are the relevant abiotic formation mechanisms known?
In this case, it's the steps to get sulfide minerals in the leopard spots that are critical. Abiotic sulfate reduction is well-studied because it sours petroleum. We know that this reaction is incredibly slow at temperatures <120 C...

My personal feeling is that, if we are wrong about anything, it will be this. Our paper provides good reasons to think that the temperature at formation was low, but the instruments on Perseverance weren't designed to make that determination with the same confidence we could in a lab on Earth...

3) How well are the conditions of formation known?
We interpret the leopard spots and poppy seeds to have formed shortly after the mud containing them settled out of a river or lake and well before the mud was turned into a rock. We also think that they formed at low temperatures, meaning <120 C...

In the case of the leopard spots and poppy seeds, the critical questions would be about the minerals we identified (ferrous sulfides and phosphates) and about the presence of organic matter. I doubt that we are going to turn out to be wrong about those detections. So far, so good...

2) How confident is the detection of the potential biosignature?
This is where many of the trace gas biosignatures on other planets have interesting questions. Methane on Mars, phosphine on Venus, and DMS on K2-18 have all had questions about whether they were correctly identified...

I ask five questions about new claims for extraterrestrial life. 1) Is the new biosignature so complex that it must have been alive? *We have never found extraterrestrial fossils like this, including the new Martian structures.* They don't even exist for the first billion years of Earth life!

The debates in the 1990s and early 2000s over the famous Martian meteorite ALH84001 and over when life first arose on Earth both drove the field to treat evidence for life in that way. As a result, we now know a lot more about how different processes can mimic things that organisms do...

Skepticism about potential biosignatures is a good place to start. Living things mostly perform reactions that happen without life. That's why specialists don't talk about things only life can produce, they talk about things that non-life is unlikely to make under the conditions they formed in...

Image collected by WATSON on the Perseverance rover of "Cheyava Falls," a rock on Mars containing potential biosignatures

I've been asked a few times over the last few days what I think the chances are that the "leopard spots and poppy seeds" on Mars will turn out to be actual evidence of life. People are naturally skeptical given the history of possible signs of life on other planets. Strap in: long thread ahead...

YouTube video by This Week in Space Life on Mars? - With Dr. Michael Tice

I had a great discussion today about the potential biosignatures found by Perseverance with the fun and insightful folks at This Week In Space (@twit.tv). Check it out here: youtu.be/MbDEslwnkdI?...

Thank you, Gwen!