
A New Recipe for Hunting Alien Life - JJLongusa
https://www.scientificamerican.com/article/a-new-recipe-for-hunting-alien-life/
======
vanderZwan
This reminds me of one of my favourite pieces of science writing ever: _"
Bands of Iron"_, by Adam Lee[0]. I don't think I've ever read something that
better conveyed a sense of Deep Time[1] in the context of life on this planet:

> _Unlike today, there were no oxygen-breathing animals to expire carbon
> dioxide and close the cycle, and so it quickly built up in the atmosphere as
> photosynthetic bacteria spread and thrived. To us, it’s the breath of life,
> but to these bacteria, it was a deadly toxin._

Luckily for these bacteria, there was iron that could react with this oxygen,
keeping the atmosphere liveable for a while. That is, until the iron ran out
and oxygen build up in deadly concentrations:

> _The consequence was mass death among the planet’s abundant bacterial
> colonies – an oxygen holocaust that knocked life back down to nearly
> nothing. Only a few anaerobes survived, in isolated nooks and crannies where
> the deadly gas did not reach._

> _After this catastrophe, the planet would have seen several million years of
> relative quiet. In this life-poor era, layers of silica minerals were
> deposited on the ocean floor. But in the meanwhile, erosion continued to
> free up iron atoms, which slowly scrubbed the atmosphere and oceans of
> oxygen._

> _Eventually, the world was cleansed, and life bounced back, spreading from
> its refuges to once again cover the planet. Of course, this exuberance
> contained the seeds of its own downfall – bacteria still spewed out the
> waste oxygen that they could not abide – and the cycle repeated, not just
> once but many times. Each time, a layer of iron oxides was deposited,
> followed by a layer of iron-poor silicates in the aftermath._

It took almost _a billion years_ before aerobic bacteria evolved and broke the
cycle. Think about that: for about a third of the entire time life has existed
on this planet, it was stuck in this self-destructive loop.

EDIT: What this story also shows is how much of Earth's geology is a result of
the presence of life, and I recall reading articles of scientist trying to
figure out if that could be used to detect the presence of life. Although I
guess that measuring the chemical composition of the rocks on another planet
would be even harder to measure than the atmosphere.

[0]
[http://www.patheos.com/blogs/daylightatheism/2009/02/bands-o...](http://www.patheos.com/blogs/daylightatheism/2009/02/bands-
of-iron/)

[1]
[https://en.wikipedia.org/wiki/Deep_time](https://en.wikipedia.org/wiki/Deep_time)

------
randomdrake
Study: Disequilibrium biosignatures over Earth history and implications for
detecting exoplanet life

Citation: Joshua Krissansen-Totton; Stephanie Olson; David C. Catling; Science
Advances 24 Jan 2018.

Link:
[https://dx.doi.org/10.1126/sciadv.aao5747](https://dx.doi.org/10.1126/sciadv.aao5747)

DOI: 10.1126/sciadv.aao5747

Abstract: Chemical disequilibrium in planetary atmospheres has been proposed
as a generalized method for detecting life on exoplanets through remote
spectroscopy. Among solar system planets with substantial atmospheres, the
modern Earth has the largest thermodynamic chemical disequilibrium due to the
presence of life. However, how this disequilibrium changed over time and, in
particular, the biogenic disequilibria maintained in the anoxic Archean or
less oxic Proterozoic eons are unknown. We calculate the atmosphere-ocean
disequilibrium in the Precambrian using conservative proxy- and model-based
estimates of early atmospheric and oceanic compositions. We omit crustal
solids because subsurface composition is not detectable on exoplanets, unlike
above-surface volatiles. We find that (i) disequilibrium increased through
time in step with the rise of oxygen; (ii) both the Proterozoic and
Phanerozoic may have had remotely detectable biogenic disequilibria due to the
coexistence of O2, N2, and liquid water; and (iii) the Archean had a biogenic
disequilibrium caused by the coexistence of N2, CH4, CO2, and liquid water,
which, for an exoplanet twin, may be remotely detectable. On the basis of this
disequilibrium, we argue that the simultaneous detection of abundant CH4 and
CO2 in a habitable exoplanet’s atmosphere is a potential biosignature.
Specifically, we show that methane mixing ratios greater than 10−3 are
potentially biogenic, whereas those exceeding 10−2 are likely biogenic due to
the difficulty in maintaining large abiotic methane fluxes to support high
methane levels in anoxic atmospheres. Biogenicity would be strengthened by the
absence of abundant CO, which should not coexist in a biological scenario.

------
poelzi
The fermi paradox bothered me quite a bit, like all paradoxes and they should
bother everybody. They are a flag that something does not add up and there
must be some sort of wrong assumption somewhere. As most of our combined
"knowledge" does not add up correctly just one example is quantum mechanics
and relativity - no, they do not add and therefor need higher dimensions to
have a model (a emergency hatch).

It is quite funny when you understand that 2 general believed assumptions are
the root cause for all the strangeness in our psysical models and very far
down the line it explains why we will never receive alien EM signals in the
area we a searching in - really makes no sense to scan there.

Non the less, I appreciate their efforts.

~~~
pavel_lishin
It's not really a paradox, right? It's just a big equation and we're guessing
at the variables.

~~~
Chathamization
We also have no reason to believe that we'd be able to detect other
civilizations, even if there were millions out there. They might well be using
other means of communication. Even if they were using the very thing we were
looking for, it's still likely we would miss them - even if they were right
next door to us. From SETI's FAQ[1]:

> If an extraterrestrial civilization has a SETI project similar to our own,
> could they detect signals from Earth?

> In general, no. Most earthly transmissions are too weak to be found by
> equipment similar to ours at the distance of even the nearest star. But
> there are some important exceptions. High-powered radars and the Arecibo
> broadcast of 1974 (which lasted for only three minutes) could be detected at
> distances of tens to hundreds of light-years with a setup similar to our
> best SETI experiments.

It always seemed odd to me that people call this a paradox.

[1] [https://www.seti.org/faq#obs1](https://www.seti.org/faq#obs1)

~~~
poelzi
From the perspective I gathered through understanding a very beautiful unified
theory (not my model) - this is exactly my point. EM waves as we use it are
useless for long distance communications. I even doubt that those waves will
still be detectable in a different solar system as the general assumptions
that our vacuum is a very homogeneous is not true for me (the underlaying
dimensions are for me, but not the vaccum as we know it). I have much more
effects that cause disturbances of such waves. Inside a solar system, there
are also better techniques that are more stable in propagation then our Hertz
EM waves. But unfortunately, we adopted a form of Maxwell Equations that are
not suitable to describe the phenomena (the original equations in quaternion
math can however). Nicolas Tesla did a lot of research in this area, but it is
not very well known/understood. (From the model I'm using 3 forms are derived.
As far as I dug into Tesla, he worked with 1 form. The 3rd form is the
interesting one but very hard to produce /detect.)

------
rthomas6
I'm going to try to put into words something about our methods of hunting for
alien life that has always bothered me, and I'm probably going to fail.

What is intelligence in the context of extraterrestrial life? I posit that we
have no good model for what intelligence actually is, and that it makes no
sense to assume any alien lifeform would share our goals of seeking knowledge,
reproduction, preservation, or "living well". These are goals tied up very
much with how life on this planet evolved. What if instead of life being on a
one-dimensional axis of "intelligence", each isolated biome evolves unique
properties for continued existence on its own planet, with very little
overlap? What makes our "intelligence" special or even desirable, outside of
furthering our own evolutionarily programmed goals? Take those very specific
goals away, and intelligence becomes something without a definition.

This leads to a more fundamental question. What is life in the context of
extraterrestrial life? How do we define success for an alien lifeform? Its
continued existence? ...But in what form? Over what timescale? On what
physical scale? How do we even know if any life we may find is alive or dead?
I think these are not pointless philosophical questions, but something that
should guide our efforts. How would we even recognize life if we found some?
Are we even _looking_ for life, or are we merely looking for life _similar to
Earth_? Surely Earth-similar life would be much more rare than just life, but
we seem to think "life" will exist on other planets with function similar to
Earth, if not form. Why assume this? A lot of Earth's life's functioning is
derived from how it evolved and how it's composed.

I think this may be part of the answer to the Fermi Paradox. Perhaps it's a
faulty assumption that intelligent life would want things like we do, and
perhaps it's a faulty assumption that intelligence is even a real thing, in a
context outside of Earth. Perhaps it's also faulty to assume that all life
will have evolutionary goals similar to Earth's.

~~~
showerst
One softball answer to that is that any civilization that doesn't get off of
its home planet is likely to go extinct, so there's less chance of it actively
modifying the environment in ways we can detect. It's also less likely to need
to develop long range, high powered communications that we can detect.

At the moment I think the idea that we're only looking for life that fits some
definition of success is specious, we're looking for any life we can find! It
happens that a big, spread out civilization that looks like us is more likely
to emit something we can see, be it atmospheric, electromagnetic, etc, just by
nature of being in more places in space and having a larger footprint.

There are astrobiologists who spend a lot of time thinking about what life may
look like, but when it comes to where to put limited resources, we start with
what we know to look for (us), and go from there.

You might be interested in the book 'weird life' by David Toomey, which tries
to theorize about what some more exotic living things might look like in the
galaxy, and expounds on some of these definitional questions.

------
goblin89
TL;DR:

With existing technology it’s tough to detect oxygen on smaller far-away
planets. However, what we could instead look for is a combination of gases
that likely means presence of life on earlier stages, before oxygen becomes
abundant in the atmosphere. (The assumption is that the alien life we might
find would likely be on early stages of development anyway.)

This research is about how such a combination of gases—lots of carbon dioxide,
methane, and no carbon monoxide—can be detected and told apart from possible
nonliving sources. The new approach should be viable to apply using Webb
telescope on smaller planets like the ones in TRAPPIST-1 system.

~~~
pecg
I'm not a scientist by any means, but since childhood when I was first exposed
to the fact that life on Earth needs oxygen (and many other things, in
extremely basic terms) to exist, I've been thinking to myself what if there
are other distant planets where life has bootstrapped itself from completely
different (or maybe opposite) components and conditions. I'm sure someone with
more knowledge than I in biology and physics would certainly be able to offer
a good explanation or thought.

~~~
taeric
I think the problem there is simply the fact that it isn't knowable. If there
is a way for life to be that different, how do you look for it?

My first statement is likely stronger than it needs to be. My main question
back to you is, how do you look for something that you imagine may exist, but
couldn't say how?

~~~
pecg
> My first statement is likely stronger than it needs to be. My main question
> back to you is, how do you look for something that you imagine may exist,
> but couldn't say how?

I certainly agree with you, thus seeking for life similar than ours is the
only feasible way to spend time in deep space research; we cannot look for
something different, because we don't know what to look for.

~~~
taeric
My apologies on the very late response, but if you haven't read it, I
recommend the book The Eerie Silence. Covers a lot of this general idea.

[https://smile.amazon.com/Eerie-Silence-Renewing-Search-
Intel...](https://smile.amazon.com/Eerie-Silence-Renewing-Search-
Intelligence/dp/B00BTM75Q0)

------
louithethrid
Imagine one human probe, with one little algea splash landing in a ocean
there. We would be the re-creators of the green goo scenario.

~~~
outworlder
We planetary protection directives, you know.

~~~
louithethrid
All those rule books, but it takes just one butt scratch on the way back from
the interplanetary probe toilett to unfold this scenario. Poor europe.

Honestly, after seeing those anti-corruption rule books - and on the same
homepages where they are displayed, the markers in countrys where you cant to
buisness without - sort a contamination scenario in itself, i doubt that
anything can prevent this once the dice with the one killing side gets re
rolled often enough.

So my money would be on less philosophers employed, more disease-control
specialists, which would quickly introduce counter agents that could be
consumed by the local flora/fauna.

