What makes the Earth habitable?

[neufer]

The one thing I'm pretty confident of is that technological civilizations are very rare. We should observe them, otherwise, and I simply don't find any of the explanations that suggest they are present but somehow unseen to be convincing at all.

<<Italian physicist Enrico Fermi suggested in the 1950s that if technologically advanced civilizations are common in the universe, then they should be detectable in one way or another. (According to those who were there, Fermi either asked "Where are they?" or "Where is everybody?")

The Fermi paradox can be stated more completely as follows:

The size and age of the universe incline us to believe that many technologically advanced civilizations must exist. However, this belief seems logically inconsistent with our lack of observational evidence to support it. Either

(1) the initial assumption is incorrect and technologically advanced intelligent life is much rarer than we believe, or

(2) our current observations are incomplete and we simply have not detected them yet, or

(3) our search methodologies are flawed and we are not searching for the correct indicators.

Possible explanations for the paradox suggest, for example, that while simple life may well be abundant in the universe, intelligent life may be exceedingly rare. In 2000, Peter Ward, professor of Biology and of Earth and Space Sciences at the University of Washington authored a book claiming the Rare Earth hypothesis. In short, the theory claims that the emergence of complex multicellular life (metazoa) on Earth required an extremely unlikely combination of astrophysical and geological events and circumstances. This hypothesis contradicts the principle of mediocrity, which SETI takes as an assumption.

Another suggestion, made by astrophysicist Ray Norris in 2000 (and subsequently by Allen Tough) was that gamma-ray burst events are sufficiently frequent to sterilize vast swaths of galactic real-estate. This idea was subsequently popularized by physicist Arnon Dar, and described in the show Death Star on PBS Nova.

Science writer Timothy Ferris has posited that since galactic societies are most likely only transitory, an obvious solution is an interstellar communications network, or a type of library consisting mostly of automated systems. They would store the cumulative knowledge of vanished civilizations and communicate that knowledge through the galaxy. Ferris calls this the "Interstellar Internet", with the various automated systems acting as network "servers".

If such an Interstellar Internet exists, the hypothesis states, communications between servers are mostly through narrow-band, highly directional radio or laser links. Intercepting such signals is, as discussed earlier, very difficult. However, the network could maintain some broadcast nodes in hopes of making contact with new civilizations.

Although somewhat dated in terms of "information culture" arguments, not to mention the obvious technological problems of a system that could work effectively for billions of years and requires multiple lifeforms agreeing on certain basics of communications technologies, this hypothesis is actually testable.

An alternate hypothesis is that evolutionary pressures in many environments favor species which rapidly consume available resources once they achieve dominance. By the time they have achieved sufficient technology to come to the notice of other civilizations, they are already well on their way to exhausting the resources of their host planet. Therefore the time period available for communication is finite, and very small compared with planetary timescales.>>

[THX1138]

As per that ending, alternate hypothesis from neufer
Wow

[bystander]

• xkcd: The Flake Equation
  

  

  Click to view full size image

[neufer]

xkcd: The Flake Equation

Of course, such arguments cut two ways:

"The Great Martian Chase," [Senator Richard Bryan of Nevada] said [in 1993], "may finally come to an end. As of today millions have been spent and we have yet to bag a single little green fellow. Not a single Martian has said take me to your leader, and not a single flying saucer has applied for FAA approval."

The Search for Extraterrestrial Intelligence: A Short History
Part 12: SETI goes to Washington
--Amir Alexander : The Planetary Society

<<From the begining, NASA's Microwave Observing Program (MOP) faced a bumpy ride. As early as 1979 Senator William Proxmire awarded the program his infamous Golden Fleece Award," given to wasteful programs sponsored by the Federal government. In 1982 Proxmire actually managed to cut all federal funding for MOP through a legislative amendment, threatening to put an end to the entire effort. The threat was averted through the timely intervention of Carl Sagan, who met personally with the Senator and convinced him that SETI was a worthwhile pursuit. Sagan then introduced a petition in support of SETI signed by many of the world's leading scientists, including seven Nobel laureates. The publicity and prestige Sagan generated kept the NASA SETI program on track for another decade.

On October 12, 1992, 500 years to the day after Columbus landed in the New World, the two NASA searches were finally launched. The Ames search began to scan its 800-1000 targeted stars from the 305-meter (1000-foot) radio telescope in Arecibo, Puerto Rico, the largest dish in the world. The JPL program began mapping the skies using the 34-meter dish at the Deep Space Communications Complex in Goldstone in the Mohave Desert. The searches were also given a new NASA designation - High Resolution Microwave Survey (HRMS).

Both searches utilized the most advanced technology available. The targeted search would analyze the spectrum between 1 and 3 GHz looking for narrow band signals. To accomplish this, its Multi Channel Spectrum Analyzer would analyze a 20 MHz wide band at any given moment, parse it into 20 million 1 Hz channels, and look for signals at bandwidths of between 1 and 28 Hz.

The JPL search was designed to map the entire sky at frequencies ranging from 1 GHz to 10 GHz. This enormous 9 GHz band would be analyzed by the Wide Band Spectrum Analyzer, designed to scan a bandwidth of 320 MHz simultaneously, and parse it out into sixteen million 20 Hz-wide channels. It would create a mosaic of 25,000 frames making up the entire night's sky. If we consider that 15 years earlier Big Ear was searching a mere 50 channels, we get a sense of the magnitude of the technological achievement involved.

But less than one year after their launch, both searches were suddenly and irrevocably terminated, victims of a new wave of Congressional budget cuts. This time it was Senator Richard Bryan of Nevada who led the charge against governmental expenditures on SETI. "The Great Martian Chase," he said, "may finally come to an end. As of today millions have been spent and we have yet to bag a single little green fellow. Not a single Martian has said take me to your leader, and not a single flying saucer has applied for FAA approval."

After an investment of around $60 million over 23 years, and less than one year of operation, NASA's SETI project was unexpectedly dead. Nevertheless, despite the crushing disappointment to SETI enthusiasts caused by the cancellation of the most ambitious search ever attempted, it can now be said that HRMS did not die in vain. The enormous resources available to NASA supported remarkable technological advances, which would have been very difficult to achieve without such backing. Furthermore, the equipment used in the Ames targeted search did not go to waste, but was passed on to the privately funded SETI Institute. The Institute then used to launch its own targeted search, the ongoing and aptly named "Project Phoenix."

Although the NASA searches were incomplete and short-lived, they completely transformed the face of SETI. Compared to the relatively amateurish efforts of previous searches, SETI became a professional enterprise conducted by experts using the most advanced technologies available. The scope and sophistication of the searches has also been increased by an order of magnitude through NASA's involvement. And though NASA is no longer an active participant in SETI, the existing SETI programs all took shape under the influence of its impressive effort.>>

[neufer]

xkcd: The Flake Equation

<<In ufology, a close encounter is an event in which a person witnesses an unidentified flying object. This terminology and the system of classification behind it was started by astronomer and UFO researcher J. Allen Hynek, and was first suggested in his 1972 book The UFO Experience: A Scientific Inquiry. He introduced the first three kinds of encounters; more sub-types of close encounters were later added by others, but these additional categories are not universally accepted by UFO researchers, mainly because they depart from the scientific rigor that Hynek aimed to bring to ufology.

Sightings more than 500 feet (160 m) from the witness are classified as "Daylight Discs," "Nocturnal Lights," or "Radar/Visual Reports."Sightings within about 500 feet are subclassified as various types of "close encounter." Hynek and others argued a claimed close encounter must occur within about 500 feet to greatly reduce or eliminate the possibility of misidentifying conventional aircraft or other known phenomena.

Hynek's scale achieved cachet with the general public when it informed elements of the 1977 film Close Encounters of the Third Kind, which is named after the third level of the scale. Posters for the film recited the three levels of the scale, and Hynek himself makes a cameo appearance near the end of the film. The Fourth level of the scale, not on Hynek's original version, in turn inspired the 2009 film The Fourth Kind.
--------------------------------------------
___ First

A sighting of one or more unidentified flying objects:

* Flying saucers
* Odd lights
* Aerial objects that are not attributable to known human technology
--------------------------------------------
___ Second

An observation of a UFO, and associated physical effects from the UFO, including:

* Heat or radiation
* Damage to terrain
* Crop Circles
* Human paralysis (Catalepsy)
* Frightened animals
* Interference with engines or TV or radio reception.
* Lost Time: a gap in one's memory associated with a UFO encounter.
--------------------------------------------
___ Third

An observation of what Hynek termed "animate beings" observed in association with a UFO sighting. Hynek deliberately chose the somewhat vague term "animate beings" to describe beings associated with UFOs without making any unfounded assumptions regarding the beings' origins or nature. Hynek did not necessarily regard these beings as "extraterrestrials" or "aliens." Additionally, Hynek further expressed discomfort with such reports, but felt a scientific obligation to include them, at the very least because they represented a sizable minority of claimed UFO encounters.
.........................................
___ Bloecher subtypes

The UFO researcher Ted Bloecher proposed seven subtypes for the close encounters of the third kind in the Hynek's scale.

A: An entity is observed only inside the UFO

B: An entity is observed inside and outside the UFO

C: An entity is observed near to a UFO, but not going in or out.

D: An entity is observed. No UFOs are seen by the observer, but UFO activity has been reported in the area at about the same time

E: An entity is observed. But no UFOs are seen and no UFO activity has been reported in the area at that time

F: No entity or UFOs are observed, but the subject experiences some kind of "intelligent communication"
--------------------------------------------
___ Fourth

A human is abducted by a UFO or its occupants. This type was not included in Hynek's original close encounters scale. Jacques Vallee, Hynek's erstwhile associate, argued that a CE4 should be described as "cases when witnesses experienced a transformation of their sense of reality," so as to also include non-abduction cases where absurd, hallucinatory or dreamlike events are associated with UFO encounters.
--------------------------------------------
___ Fifth

Named by Steven M. Greer's CSETI group, these purported encounters are joint, bilateral contact events produced through the conscious, voluntary and proactive human-initiated or cooperative communication with extraterrestrial intelligence. This is very similar to some "contactees" of the 1950s who claimed regular communication with benevolent aliens.
--------------------------------------------
___ Sixth

On Michael Naisbitt's website, a sixth proposed CE scenario is described as UFO incidents that cause direct injury or death. This category was not included in Hynek's scale, and is furthermore redundant: a CE2 in Hynek's scale specifically included UFO encounters that leave direct physical evidence of any kind.
--------------------------------------------
___ Seventh

The Black Vault Encyclopedia Project proposes a Close Encounter of the Seventh Kind as human-alien hybridisation.[9] This concept similar to ideas promoted by ancient astronauts theorists like Erich von Däniken, Zecharia Sitchin and Robert K.G. Temple, in that extraterrestrials interacted with, perhaps interbred with and influenced ancient human beings in the past.

This concept of CE7 is at odds with Hynek's original concepts, however. Hynek's CE3 specifically avoided describing UFO occupants as "aliens" or "extraterrestrials," contending that there was not enough evidence to determine if beings associated with UFOs had an objective physical reality, let alone to confirm their origins or motives.
--------------------------------------------
___ Eighth

A Close Encounter of the Eighth Kind has been depicted in fiction by television shows such as X-Files, V (science fiction)KV, Alien Nation, Stargate: SG-1, They Live, and First Wave, CE8 refers to possible alien colonization. According to the ancient astronaut theory, extraterrestrials today are producing hybridised human beings to infiltrate key government positions throughout the world in an effort to:

a) continue the alien astronaut philosophy to assist humanity in what these extraterrestrials deem human infancy today and prepare the species for future endeavors,

b) control the world through a New World Order,

c) annihilate human existence for any varying reasons such as damages to the Earth itself or threats to the rest of the universe from human progress and thinking, or

d) a simply, malevolent species bent on eradicating all life other than their own.
--------------------------------------------
___ Ninth

A Close Encounter of the Ninth Kind is termed Revelation. For a CE9 to take place, an extraterrestrial race would openly reveal themselves to humanity, forever lifting a veil of secrecy in regards to alien involvement in human affairs.
--------------------------------------------

[bystander]

Recreate life to understand how life began
New Scientist | Opinion | 09 Aug 2010

Building artificial cells will tell us much about the origins of life – and may explain how Darwinian evolution began, says Nobel laureate Jack Szostak

IMAGINE Earth 4 billion years ago. It is a world of oceans, peppered with volcanic land masses resembling Hawaii and Iceland. The volcanoes spew poisonous gases and the atmosphere is rent by the violent impacts of asteroids and comets. Temperatures range from the incandescent heat of flowing lava to the frozen ice fields of the high polar regions. Shallow ponds on the volcanic islands dry out, then fill with rain, incubating the fragile chemistry that ultimately leads to the emergence of life.

How extraordinary that cellular life should have arisen in such a harsh environment. The exact nature of that first cell, the basic unit of all life today, is still unknown. It is an exciting puzzle that goes to the heart of the origins of life as we know it. But it is hard to solve: after all, reconstructing such ancient events seems an impossible task. Fortunately, there is much to be learned from a slightly more modest goal: building basic artificial cells in the lab ...

[neufer]

I think of it this way: there's a million ways a tool-building species can go wrong, but there's a million and one ways for it to recover. In other words, I feel the positive creativity slightly outweighs the stupidity. And slightly is all we need, though the road can be mighty bumpy along the way.

BEWARE OF KILLER TORTOISES
David S. Lee. Terrapin Tails 2(3):6

<<The first thing you notice about the marble bust are the eyes. The practice of not including pupils as part of the eye in sculpted busts imparts a distinctive far-off stare. Well, perhaps this is fitting; the poor guy has been dead for over 2,000 years. The white marble head, believed to be a likeness of Aeschylus, can be seen in the Capitoline Museum in Rome where it sits on its own pedestal partway down a long row of other famous heads. This particular bust's second prominent feature is the bald cranium emphasized by the smooth, polished stone. Aeschylus (525~65 BC), in case you've forgotten, is considered the father of Greek drama. His poetic work, with its distinctive vigor and lofty tone, still survives in seven extant plays and fragments of more than 70 others. In addition to his writing, Aeschylus was renowned for his heroic acts as a soldier in Greece's perennial war with Persia. Of more relevant interest to us is Aeschylus' death. It turns out Aeschylus was a victim of his own bald head. According to tradition, he survived hordes of warring mongrels only to be killed by a tortoise.

Click to play embedded YouTube video.

Lammergeier vultures were apparently more common in southern Europe 2,000 years ago than they are today. Carrion feeders, they specialize on the bones of deceased animals that other vulture species leave behind. Lammergeiers learned to carry large bones high in the air and drop them on rocks before descending to feed on the exposed marrow. They learned that this method also works for opening up tortoise shells. Apparently, the top of Aeschylus' living head and its marble likeness are similar, at least from a vulture's view. Had Aeschylus lived through the experience, perhaps the secrets of gravity would have recorded 2,107 years before Sir Isaac Newton was born. But as every schoolchild knows, that is not the case. Lammergeiers have good aim, and the poet died on the spot. The story of Aeschylus' death has been passed on through the ages. and there is even a record of one balding man adding a "cause of death from a falling tortoise" clause to his life insurance policy. Surely, there's a moral in all this; after all, that is what Greek literature was built around. If I have interpreted this correctly, one can set aside all biological and behavioral information, noble bearing, talent and heroic virtue and simply remember to beware of Greek vultures bearing gifts.>>

[Colin Robinson]

Planets and moons are surprising.

Yes!

That is why I'd suggest that it is important not to jump to conclusions, about what sort of things or processes may or may not be present on unexplored worlds.

When I was a kid in the sixties, my parents had a coffee table Reader's Digest style book about the natural world. I read that book a lot, and I definitely thought that it was serious. My favorite chapter was one that predicted that people in the year 2000 would visit Mars in the same way that people in the sixties visited Hawaii... Getting to see Mars would be a lot of fun... be able to admire the Martian vegetation, which was undoubtedly the cause of the seasonal variation of the coloring of the Martian landscape which could be seen from the Earth.

Like you, Ann, I grew up in the sixties, and I remember the negative surprises that came when space probes found that Mars was cratered rock rather than flourishing fields of exotic vegetables, and that the surface of Venus was neither ocean nor jungle, but arid and extremely hot...

The idea that life may exist in the incredibly cold lakes of Titan seems even more far-fetched.

Why does that idea seem so far-fetched?

It seems to me that Titan has been surprising us in the opposite way to Mars and Venus -- though far outside the presumed habitability zone, it turns out to be unexpectedly Earth-like.

Some of Titan's Earth-like characteristics -- e.g. fact that the surface has relatively few impact craters -- might seem tangential to the question of possible life there...

A less tangential point is that Titan and Earth are the only two worlds known to have both large carbon-based molecules and liquid solvents.

And, most recently, there is evidence that something is consuming both hydrogen and carbon-chain molecules at or near the surface.

Whether it is life or not, it is surely worth a closer look...

Colin

[BMAONE23]

Our oceans support life because of Dissolved Oxygen in the water. When fish respirate, they aren't stripping the O from the H2O, they are removing dissolved oxygen from the water through their gills. The Eatrh Water Cycle acts to replinish the dissolved oxygen, from our atmosphere, so that the sea life can continue their cycle. I am curious as to what mechanism is proposed to replinish dissolved oxygen in a Moon like Europa that has no Atmosphere or similar water cycle.

[Henning Makholm]

Our oceans support life because of Dissolved Oxygen in the water.

For the first one or two billion years of life on Earth, the oceans supported life without any appreciable amount of oxygen dissolved in them. The life forms of that era thrived perfectly well without free oxygen, which in fact was toxic to most of them -- lots of things went extinct after some irresponsible bacteria started using a carbohydrate synthesis pathway that produced deadly, corrosive O2 as a waste product. It was the first major pollution catastrophe in the planet's history.

[Colin Robinson]

Our oceans support life because of Dissolved Oxygen in the water. When fish respirate, they aren't stripping the O from the H2O, they are removing dissolved oxygen from the water through their gills. The Eatrh Water Cycle acts to replinish the dissolved oxygen, from our atmosphere, so that the sea life can continue their cycle. I am curious as to what mechanism is proposed to replinish dissolved oxygen in a Moon like Europa that has no Atmosphere or similar water cycle.

Europa actually does have an atmosphere, though an extremely thin one. It is composed mainly of oxygen molecules, apparently generated by the effect of UV radiation and charged particles on the surface ice. This contrasts with the situation on Earth, where the oxygen is generated by plants, as a byproduct of photosynthesis.

The suggestion is that some of the oxygen generated at Europa's surface may find its way into the subsurface ocean, where (as on Earth) it would become dissolved and could provide an energy source for organisms swimming about there.

For more details, have a look at the Wikipedia entry
http://en.wikipedia.org/wiki/Europa_(moon).

[Colin Robinson]

Our oceans support life because of Dissolved Oxygen in the water.

For the first one or two billion years of life on Earth, the oceans supported life without any appreciable amount of oxygen dissolved in them. The life forms of that era thrived perfectly well without free oxygen, which in fact was toxic to most of them -- lots of things went extinct after some irresponsible bacteria started using a carbohydrate synthesis pathway that produced deadly, corrosive O2 as a waste product. It was the first major pollution catastrophe in the planet's history.

Which is one reason why Titan, which seems to have no free oxygen, may be as habitable, or more habitable than Europa, which does have free oxygen...

[Beyond]

What makes the Earth habitable?? NOTHING!! that's why everything DIES!!

[BMAONE23]

I think we would be extremely overcrowded if nothing ever died. There would be few new trees as the sun couldn't reach the ground through the planet wide canopy. There would be about 12 billion people with half being over 200 and many being 20-30,000+ years old. There would be no agriculture to support the masses because harvesting kills plant life and nothing ever dies.

Nah
out with the old and in with the new.