Alone in the Universe

I’m still postponing the ultra-long post about my conclusions about the MOST INTERESTING MODULE EVER because, in a nutshell, the course isn’t over yet.
But don’t worry…recall that lecture I had just last week about Life in The Universe?

Prof Guillermo Gonzalez from Iowa State University came down to talk about Life In the Universe. I was half-hoping half-praying that it would go into speculative areas [little green men. yay!] and NOT become TOO speculative at the same time. I tend to be rational most of the time see? And let me assure you, it was a bit too theoretical; I’m actually more amazed now about the odds of life having originated at all.

All the following are excerpts from his lecture and the ideas they embody belong to him. If I get ideas of my own, I’ll type them in “[ … ]” okay?

Astrobiology is the interdisciplinary field of speculative science that theorizes where life can be found in the Universe.

Life is defined as anything that has a DNA equivalent and is able to pass it on in some way. [This definition actually got me worried too? So sentience doesn’t matter? And does it necessarily mean life MUST be short-lived, cosmically speaking?]
Since carbon is the only atom that is capable of such length and complexity required by DNA [or equivalent] to encode biological information, and water is the only compound that supports life as a result of its anamolous properties, we might expect that, using ourselves as the only case study, that any other lifeform might need the same chemicals to live as well.
Any other element has no proven working model. [Well there’s definitely the case of extremophiles but no one knows if the conditions required can work on a planetary scale]

Among Life’s needs are the chemicals available. Moreover as a planet [or celestial body], there must be a geophysical set of chemical cycles to keep “cycling” these compounds so that life processes have something to work at, towards, or even against. Energy in the universe comes almost exclusively from “star”light and it can be assumed [at least initially] that oxygen plays a major role as well.

So minimum requirements for life are:
C, H2O, O2, and other elements,
the means to cycle the various elements,
and temperature stability for organic reactions [a buffer region of max 30o]

So, the Circumstellar Habitable Zone [CHZ] is the region around a star that can maintain water in liquid form. So within this region, the ratio of incoming energy from the star and radiated energy by the planet [surface temperature] must be just right to maintain the range required by water to stay liquid. That’s including the buffering effects of atmosphere.
If too close to the inner boundary [closer to star], there’d be a runaway greenhouse effect. and if too far away from the star, there’d be runaway glaciation.

The carbonate-silicate cycle can be roughly summarised into three chemical equations which I WONT type out here. But it’s a surprisingly “big” process.

1. Carbonated rain reacting with land masses [Calcium Silicate] gives rise to hydrogen-carbonate ions and SiO2. This process is extremely temperature dependant and along with photosynthesis, help to remove CO2 from the atmosphere at variable rates.

2. In the seas, calcium ions react with hydrogen-carbonate releasing carbon dioxide.

3. And tectonic activity, giving rise to volcanic activity, also releases CO2.

IF temperature in this system is increased, process 1 [including photosynthesis] works more efficiently removing more CO2 leaving less greenhouse gases in the atmosphere allowing more heat to be radiated away from the planet, thus cooling it. Wonderfully elegant.

Also having a moon might affect the planet’s rotation, unless it’s the right distance away. If there is [effectively] no moon, then there won’t be tides at all, and that might affect life processes that depend on them. Considering life on Earth originated in the oceans, tides may have played a significant role that we may not be aware of.
HOWEVER, if the moon is too close, then there’s a phenomenon known as tidal lock, as the gravitational pull among planet and moon slow each other down and stop the planet from rotating, causing a cold trap! That’s not to mention, eventual collision of moon with planet if they stop rotating and revolving. [I suppose it can be argued that some of the momentum of revolution comes from rotation]

Galactic Habitable Zones [GHZ] are the building blocks for habitable planets, and essential for the survival of complex life. In astronomical terms, all elements except H and He [which make up 98% of the Universe] are known as “metals”. Metallicity is increasing over time because the H and He are constantly being “used up” in the fusion processes that power the stars.

Planets in these places [GHZ] can support life cos they’re not too close to the center where there are far too many supernovae to avoid cosmic radiation.
GHZ can’t be too far away [from the center] as these solar systems were “created” earlier in the galaxy’s existence and therefore not “metallic” enough to host life. Moreover these systems may also be in the collision path of any number of comets in the galactic equivalent of Oort Cloud.

Metal-rich stars [closer to the center of the galaxy] are more likely to host giant planets. Giant planets have and cause eccentric orbits in the entire system and without the regularity of a circular orbit, any terrestrial possibly life-sustaining planet has no chance of staying within the CHZ.

Cosmic Habitable Age [CHA] began when the Universe cooled down enough [Cosmic background radiation] after the Big Bang.

The Universe is getting more metal-rich, and star formation is slowing down. The radio-isotopes that power planetary tectonics are also slowly but surely decaying. The stars will eventually run out of H, He to power their nuclear fusion. Only red dwarfs will continue to exist. So theoretically there WILL come a time when there is no energy left to “give” out in the universe. That will signal the end of the CHA.

Having a CHZ in a suitable GHZ during the CHA is so rare that despite the size of the universe, the number of possibly life-sustaining planets is easily less than 5%.

So we’re damn lucky to be alive, he’s saying. Still no to creation science though :p.


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