Aliens, area 51, UFO's and the like.

[Benguin]

I'm about as skeptical as they come with cover ups and conspiracy theories but that doesn't mean I don't like to read about them. In fact I find myself obsessing about some and even when they're dark or horrible I often can't help wanting them to be true.

 

My favorite one to read about is area 51. When it comes down to it, I think at most there are some cool pieces of technology there out with the scope of anything abnormal or sinister. That said I don't see any reason for the base to be as secretive as it is if it just a military base to test advanced aircraft and warfare. I don't buy into the national security stuff unless they are testing or hiding more. 

 

I listened to this recently and enjoyed it, as they delve into it all but with skeptical eyes. https://thoseconspiracyguys.com/area-51/

 

What do others think, about any conspiracies not just area 51?

[Jon the Hat]

I wouldn't underestimate the sensitivity of the US military, plus don't forget in the capitalist US of A this kit is mostly built by private companies, so they are also ultra security conscious about their competitors seeing what they are up to.  I have worked in a consumer tech company in the past, and you see a lot of cool stuff which never makes it to production even 15 years later, so they also don't want stuff to be seen and then not materialize as it makes them look wasteful.

[FoxyPalace.com]

I will be going on a trip to Groom Lake this year as we are going to Vegas in August.

 

Area 51 is testing for state of the art aircraft, the UFO thing was a cover up leaked by the US government to hide test flights which regulary get seen flying.

 

No Aliens I am afraid. 

[leicsmac]

Agree with the general sentiment here - Area 51 is where the bleeding-edge aircraft gets made and tested, possibly as well as other techs that the US military is looking to bring into the world. The security is huge because I'm guessing most of the tech used there are unique prototypes.

 

However, the idea of UFO's in general isn't one that can be dismissed out of hand IMO.

[Wymsey]

A thread particularly for @Zingari and @BoneDog..

Edited 20 December 2017 by Wymeswold fox

[RoboFox]

Area 51 and Nellis Airforce Base? Nothing to see here.

 

9/11 was somehow orchestrated by the US government and the buildings around the WTC were destroyed by controlled demolition? Nonsense.

 

Paul McCartney died in 1966 and was replaced by a lookalike? Absurd.

 

The Moon landings were faked and man has never actually set foot on the moon? Get a grip.

 

The Earth is flat? Oh, please...

 

The Carabao Cup draw was rigged so that none of the big clubs faced each other?

TRUE 

Edited 20 December 2017 by RoboFox

[Trav Le Bleu]

3 hours ago, Wymeswold fox said:

A thread particularly for @Zingari and @BoneDog..

Came into the thread to say exactly that

 

[Buce]

3 hours ago, leicsmac said:

Agree with the general sentiment here - Area 51 is where the bleeding-edge aircraft gets made and tested, possibly as well as other techs that the US military is looking to bring into the world. The security is huge because I'm guessing most of the tech used there are unique prototypes.

 

However, the idea of UFO's in general isn't one that can be dismissed out of hand IMO.

 

I'm surprised by you saying that, Mac.

 

Would you care to explain your reasoning?

[leicsmac]

14 minutes ago, Buce said:

 

I'm surprised by you saying that, Mac.

 

Would you care to explain your reasoning?

Most certainly.

 

Though it is at this time flawed in one particular place regarding habitability of planets, the Drake Equation is pretty conclusive - given the amount of planetary systems there are even in our locality, the odds of there being intelligent alien life out there are far higher than one might suspect. Even more so if (and again I suspect we might) find simple life on Europa or Enceladus that proves life can thrive in other places than Earth.

 

So, with all of that taken into account, the idea there might be craft about up there that aren't from Earth - while pretty damn farfetched - isn't a statistical impossibility and shouldn't be dismissed out of hand. Of course, the Fermi Paradox gives us a dozen reasons why things are conclusive on that matter (yet), and I'd be as shocked as anyone should one of these UFO sightings turn out to be a bona fide alien craft...but given scientific and mathematical probability I'm not doing to dismiss it as an option.

 

Edit: For clarification I'm talking about generalities here, not UFO's at Area 51 as I'm personally certain that isn't the case.

Edited 20 December 2017 by leicsmac

[Collymore]

9 minutes ago, Buce said:

 

I'm surprised by you saying that, Mac.

 

Would you care to explain your reasoning?

Remember the term UFO isn't necessary to do with aliens. Thousands of UFOs are spotted every day around the world as many people can't be arsed or have the means to find out what it was so they stay as UFOs.

 

As for the alien theory. If there was a briefcase with a million pounds placed in front of you and you were asked "have we been visited by aliens?"and if you answered correctly you'd get the cash, what would your gut feeling be? 

 

I think I'd say yes. 

 

 

[Bellend Sebastian]

3 hours ago, Wymeswold fox said:

A thread particularly for @Zingari and @BoneDog..

Their silence speaks volumes.

 

You know why, don't you?

 

Abducted and probed

[Benguin]

What if we are the aliens and life was brought to earth on a rock from another planet and the planet we have left followed a not too dissimilar evolutionary path and there's other humans on the original earth wandering the same thing?

[Wymsey]

5 minutes ago, Bellend Sebastian said:

Their silence speaks volumes.

 

You know why, don't you?

 

Abducted and probed

It's strange in thinking that it feels like not too long ago since they were last on here, but haven't been heard from go for a good while now.

They seemed like completely opposite poster personalities, but yet made this part of the forum in particular sometimes more intriguing to view.

Edited 20 December 2017 by Wymeswold fox

[Bellend Sebastian]

2 minutes ago, Wymeswold fox said:

It's strange in thinking that it feels like not too long ago since they were last on here, but haven't been heard from go for a good while now.

They seemed like completely opposite poster personalities, but yet made this part of the forum in particular sometimes more intriguing to view.

Mad as a box of frogs, the pair of them.

 

Always entertaining though

[Izzy]

I played golf today with a bloke who's a massive fan of David Icke - seriously.

 

We got chatting and he told me about Icke's theories and how he'd seen him talk on many occasions.

 

Must say that by the end of the round I was really intrigued to the point of maybe even buying his new book.

 

Always thought I didn't believe in all this conspiracy theory nonsense, but I'm prepared to open my mind a bit to it now...

[Benguin]

7 minutes ago, Izzy Muzzett said:

I played golf today with a bloke who's a massive fan of David Icke - seriously.

 

We got chatting and he told me about Icke's theories and how he'd seen him talk on many occasions.

 

Must say that by the end of the round I was really intrigued to the point of maybe even buying his new book.

 

Always thought I didn't believe in all this conspiracy theory nonsense, but I'm prepared to open my mind a bit to it now...

There are several from years ago that turned out to be true or partially true, so it stands to reason that one or a few of the many knocking about have some truth to it. As they say, "no smoke without fire."

 

 

[SpacedX]

Conspiracy theory is a global business. The perpetrators at the top of the tree such as the risible David Icke and Alex Jones/Infowars know exactly what they are doing and who to target whilst the advent of the internet has meant that the low hanging fruit that subscribe to this nonsense are ripe for the picking. 

 

It's nothing more than a production line, churning out one ludicrous theory after another to order. To some it may be just harmless speculative fun, but increasingly the gullible and the scientifically illiterate buy into this firstly through their emotional investment and then very often financially. It's a security blanket which people cower under and cling to It also divests, blame accountability, responsibility and assuages guilt. Belief in conspiracy gives order to a random and chaotic world full of complex explanations. There are no natural disasters anymore, they are engineered by the sinister "they", no terrorist atrocities...they are all false flags involving crisis actors. Screw education and expertise, an afternoon in front of YouTube and you are "awakened" - a "truther" - irony being, nothing could be further from it. Clickbait confirmation bias ensures you're dragged down the rabbit hole engulfed by the vacuous echo chamber and imprisoned in an online bubble. Because it thrives on ignorance, fear and prejudice, beneath the surface it also almost invariably peddles extremist agenda and in America, this is the very much the preserve of the gun toting far right and the anti semitic. 

 

Trump rails against the liberal press which he brands as fake news, seemingly remaining impervious to the fact that the latter was instrumental in placing him in power. His pre-election tweets pandered to the anti-vax movement and his campaign trail embraced the creationists of the Bible Belt and the Mid West...many of whom are now adamant that the earth is flat. This anti-science thrives in a populist world in which true knowledge and expertise is seen as elite. In this climate (no pun intended) it was easy to reverse action on global warming with the stroke of a pen and the deletion of content on the EPA website.

[SpacedX]

Back to the OP. Is there extra terrestrial life in our universe? Most definitely. Has it ever consciously visited us? Highly unlikely - the temporal and spatial barriers are simply too vast.

 

However, some will nonetheless doubtless contend that an inconceivably advanced civilisation has developed the technology to traverse thousands of light years of interstellar space purely to abduct some redneck from a trailer park in Arkansas or mutilate a herd of cattle in New Mexico.

[leicsmac]

4 minutes ago, Line-X said:

Back to the OP. Is there extra terrestrial life in our universe? Most definitely. Has it ever consciously visited us? Highly unlikely - the temporal and spatial barriers are simply too vast.

 

However, some will nonetheless doubtless contend that an inconceivably advanced civilisation has developed the technology to traverse thousands of light years of interstellar space purely to abduct some redneck from a trailer park in Arkansas or mutilate a herd of cattle in New Mexico.

I've said it before but I'll say it again - we're their Reality TV. Monkey Shore.

[Carl the Llama]

There must be billions of planets out there with life just as 'advanced' as us and probably a lot that are more so.  If that's not the case then this perplexing universe of ours makes even less sense.

[ozleicester]

9 hours ago, Wymeswold fox said:

A thread particularly for @Zingari and @BoneDog..

Both "disappeared" at a similar time....... 

 

 on further investigation, (like most good conspiracy theories) I was remember ing it wrong... there was two years between their last posts.

 

Always wondered what happened to @Zingari, if i remember he just stopped posting, ive often thought...the poor guy couldve been hit by a bus etcetc..and we would never know.

Edited 21 December 2017 by ozleicester

[Mike Oxlong]

7 hours ago, Bellend Sebastian said:

Their silence speaks volumes.

 

You know why, don't you?

 

Abducted and probed

Ooh, that sounds unpleasant! 

 

I had assumed that they had just married each other and were living happy ever after.

[Mike Oxlong]

UFO is a term used when your Mrs is asking you to move out. 

[stripeyfox]

I think the chances of us running into "intelligent" life are very slim. I love all the Drake Equation and Fermi Paradox stuff, but the "Great Filter" also tells us that although there are billions (probably) of potential life supporting planets, the chances of species being able to develop to a point where interstellar travel is possible are very very small.

 

I think the Rare Earth Hypothesis is a more accurate view

https://en.wikipedia.org/wiki/Rare_Earth_hypothesis

 

The Rare Earth hypothesis argues that the evolution of biological complexity requires a host of fortuitous circumstances, such as a galactic habitable zone, a central star and planetary system having the requisite character, the circumstellar habitable zone, a right sized terrestrial planet, the advantage of a gas giant guardian like Jupiter and a large natural satellite, conditions needed to ensure the planet has a magnetosphere and plate tectonics, the chemistry of the lithosphere, atmosphere, and oceans, the role of "evolutionary pumps" such as massive glaciation and rare bolide impacts, and whatever led to the appearance of the eukaryote cell, sexual reproduction and the Cambrian explosion of animal, plant, and fungi phyla. The evolution of human intelligence may have required yet further events, which are extremely unlikely to have happened were it not for the Cretaceous–Paleogene extinction event 66 million years ago which saw the decline of dinosaurs as the dominant terrestrial vertebrates.

In order for a small rocky planet to support complex life, Ward and Brownlee argue, the values of several variables must fall within narrow ranges. The universe is so vast that it could contain many Earth-like planets. But if such planets exist, they are likely to be separated from each other by many thousands of light years. Such distances may preclude communication among any intelligent species evolving on such planets, which would solve the Fermi paradox: "If extraterrestrial aliens are common, why aren't they obvious?"^[1]

The right location in the right kind of galaxy[edit]

Rare Earth suggests that much of the known universe, including large parts of our galaxy, cannot support complex life; Ward and Brownlee refer to such regions as "dead zones". Those parts of a galaxy where complex life is possible make up the galactic habitable zone. This zone is primarily a function of distance from the Galactic Center. As that distance increases:

1. Star metallicity declines. Metals (which in astronomy means all elements other than hydrogen and helium) are necessary to the formation of terrestrial planets.
2. The X-ray and gamma ray radiation from the black hole at the Galactic Center, and from nearby neutron stars, becomes less intense. Radiation of this nature is considered dangerous to complex life, hence the Rare Earth hypothesis predicts that the early universe, and galactic regions where stellar density is high and supernovae are common, will be unfit for the development of complex life.^[2]
3. Gravitational perturbation of planets and planetesimals by nearby stars becomes less likely as the density of stars decreases. Hence the further a planet lies from the Galactic Center or a spiral arm, the less likely it is to be struck by a large bolide. A sufficiently large impact may extinguish all complex life on a planet.

Dense center of galaxies such as NGC 7331 (often referred to as a "twin" of the Milky Way^[3]) have high radiation levels toxic to complex life.

According to Rare Earth, globular clusters are unlikely to support life.

Item #1 rules out the outer reaches of a galaxy; #2 and #3 rule out galactic inner regions. As one moves from the center of a galaxy to its furthest extremity, the ability to support life rises then falls. Hence the galactic habitable zone may be ring-shaped, sandwiched between its uninhabitable center and outer reaches.

While a planetary system may enjoy a location favorable to complex life, it must also maintain that location for a span of time sufficiently long for complex life to evolve. Hence a central star with a galactic orbit that steers clear of galactic regions where radiation levels are high, such as the Galactic Center and the spiral arms, would appear most favourable. If the central star's galactic orbit is eccentric (elliptic or hyperbolic), it will pass through some spiral arms, but if the orbit is a near perfect circle and the orbital velocity equals the "rotational" velocity of the spiral arms, the star will drift into a spiral arm region only gradually—if at all. Therefore, Rare Earth proponents conclude that a life-bearing star must have a galactic orbit that is nearly circular about the center of its galaxy. The required synchronization of the orbital velocity of a central star with the wave velocity of the spiral arms can occur only within a fairly narrow range of distances from the Galactic Center. This region is termed the "galactic habitable zone". Lineweaver et al.^[4] calculate that the galactic habitable zone is a ring 7 to 9 kiloparsecs in radius, that includes no more than 10% of the stars in the Milky Way.^[5] Based on conservative estimates of the total number of stars in the galaxy, this could represent something like 20 to 40 billion stars. Gonzalez, et al.^[6] would halve these numbers; he estimates that at most 5% of stars in the Milky Way fall in the galactic habitable zone.

Approximately 77% of observed galaxies are spiral galaxies,^[7] two-thirds of all spiral galaxies are barred, and more than half, like the Milky Way, exhibit multiple arms.^[8] What makes our galaxy different, according to Rare Earth, is that it is unusually quiet and dim (see argument below), representing just 7% of its kind.^[9] Even so, this would still represent more than 200 billion galaxies in the known universe.

A reason that our galaxy is considered rare by Rare Earth is because it appears to have suffered fewer collisions with other galaxies over the last 10 billion years, and its peaceful history may have made it more hospitable to complex life than galaxies which have suffered more collisions, and consequently more supernovae and other disturbances.^[10] The level of activity of the black hole at the centre of the Milky Way may also be important: too much or too little and the conditions for life may be even rarer. The Milky Way black hole appears to be just right.^[11] The orbit of the Sun around the center of the Milky Way is indeed almost perfectly circular, with a period of 226 Ma (1 Ma=1 million years), one closely matching the rotational period of the galaxy. However, the majority of stars in barred spiral galaxies populate the spiral arms rather than the halo and tend to move in gravitationally aligned orbits, so there is little that is unusual about the Sun's orbit. While the Rare Earth hypothesis predicts that the Sun should rarely, if ever, have passed through a spiral arm since its formation, astronomer Karen Masters has calculated that the orbit of the Sun takes it through a major spiral arm approximately every 100 million years.^[12] Some researchers have suggested that several mass extinctions do correspond with previous crossings of the spiral arms.^[13]

Orbiting at the right distance from the right type of star[edit]

 

According to the hypothesis, Earth has an improbable orbit in the very narrow habitable zone (dark green) around the Sun.

The terrestrial example suggests that complex life requires water in the liquid state, and a central star's planet must therefore be at an appropriate distance. This is the core of the notion of the habitable zone or Goldilocks Principle.^[14] The habitable zone forms a ring around the central star. If a planet orbits its sun too closely or too far away, the surface temperature is incompatible with water being in liquid form.

The habitable zone varies with the type and age of the central star. For advanced life the star must have a high degree of stability. Stars with an age of 4.6 billion years, middle star life, are at the most stable state. Proper metallicityand size are also very important to stability. The Sun has a low 0.1% solar luminosity variation. A solar twin star, would be a star with low luminosity variation. To date no solar twin with an exact match as that of the Sun has been found, however, there are some stars that come close to being identical. The star must have no stellar companions, other close by stars as in binary systems, would disrupt the orbits of planets. Estimates suggest that 50% or more of all star systems are binary systems.^{[15][16][17][18]} The habitable zone for a main sequence star very gradually moves out over time until the star becomes a white dwarf, at which time the habitable zone vanishes. The habitable zone is closely connected to the greenhouse warming afforded by atmospheric water vapor (H
2O), carbon dioxide (CO₂), and/or other greenhouse gases. Even though the Earth's atmosphere contains a water vapor concentration from 0% (in arid regions) to 4% (in rain forest and ocean regions) and – as of June 2013 – only 400 parts per million of CO₂, these small amounts suffice to raise the average surface temperature of the Earth by about 40 °C from what it would otherwise be,^[19] with the dominant contribution being due to water vapor, which together with clouds makes up between 66% and 85% of Earth's greenhouse effect, with CO₂ contributing between 9% and 26% of the effect.^[20]

Rocky planets must orbit within the habitable zone for life to form. Although the habitable zone of such hot stars as Sirius or Vega is wide:

1. Rocky planets that form too close to the star to lie within the habitable zone cannot sustain life. Hot stars also emit much more ultraviolet radiation that ionizes any planetary atmosphere.
2. Hot stars, as mentioned above, may become red giants before advanced life evolves on their planets.

These considerations rule out the massive and powerful stars of type F6 to O (see stellar classification) as homes to evolved metazoan life.

Small red dwarf stars conversely have small habitable zones wherein planets are in tidal lock—one side always faces the star and becomes very hot and the other always faces away and becomes very cold—and are also at increased risk of solar flares (see Aurelia) that would tend to ionize the atmosphere and be otherwise inimical to complex life. Rare Earth proponents argue that life therefore cannot arise in such systems and that only central stars that range from F7 to K1 stars are hospitable. Such stars are rare: G type stars such as the Sun (between the hotter F and cooler K) comprise only 9%^[21] of the hydrogen-burning stars in the Milky Way.

Such aged stars as red giants and white dwarfs are also unlikely to support life. Red giants are common in globular clusters and elliptical galaxies. White dwarfs are mostly dying stars that have already completed their red giant phase. Stars that become red giants expand into or overheat the habitable zones of their youth and middle age (though theoretically planets at a much greater distance may become habitable).

An energy output that varies with the lifetime of the star will very likely prevent life (e.g., as Cepheid variables). A sudden decrease, even if brief, may freeze the water of orbiting planets, and a significant increase may evaporate them and cause a greenhouse effect that may prevent the oceans from reforming.

Life without complex chemistry is unknown. Such chemistry requires metals, namely elements other than hydrogen or helium and thereby suggests that a planetary system rich in metals is a necessity for life. The absorption spectrum of a star reveals the presence of metals within, and studies of stellar spectra reveal that many, perhaps most, stars are poor in metals. Because heavy metals originate in supernova explosions, metallicity increases in the universe over time. Low metallicity characterizes the early universe: globular clusters and other stars that formed when the universe was young, stars in most galaxies other than large spirals, and stars in the outer regions of all galaxies. Metal-rich central stars capable of supporting complex life are therefore believed to be most common in the quiet suburbs^[vague] of the larger spiral galaxies—where radiation also happens to be weak.^[22]

With the right arrangement of planets[edit]

 

Depiction of the Sun and planets of the Solar System and the sequence of planets. Rare Earth argues that without such an arrangement, in particular the presence of the massive gas giant Jupiter (fifth planet from the Sun and the largest), complex life on Earth would not have arisen.

Rare Earth proponents argue that a planetary system capable of sustaining complex life must be structured more or less like the Solar System, with small and rocky inner planets and outer gas giants.^[23] Without the protection of 'celestial vacuum cleaner' planets with strong gravitational pull, the number of asteroid collisions may have been larger, and a greater number of mass extinction events may have occurred.

Observations of exo-planets have shown that arrangements of planets similar to the solar system are rare. Most planetary systems have super Earths, several times larger than Earth, close to their star, whereas the Solar System's inner region is depleted in mass with small rocky planets and none inside Mercury's orbit. Only 10% of stars have giant planets similar to Jupiter and Saturn, and those few rarely have stable nearly circular orbits distant from their star. Konstantin Batygin and colleagues argue that these features can be explained if, early in the history of the Solar System, Jupiter and Saturn drifted towards the Sun, sending showers of planetesimals towards the super-Earths which sent them spiralling into the Sun, and ferrying icy building blocks into the terrestrial region of the Solar System which provided the building blocks for the rocky planets. The two giant planets then drifted out again to their present position. However, in the view of Batygin and his colleagues: "The concatenation of chance events required for this delicate choreography suggest that small, Earth-like rocky planets – and perhaps life itself – could be rare throughout the cosmos."^[24]

A continuously stable orbit[edit]

Rare Earth argues that a gas giant must not be too close to a body where life is developing. Close placement of gas giant(s) could disrupt the orbit of a potential life-bearing planet, either directly or by drifting into the habitable zone.

Newtonian dynamics can produce chaotic planetary orbits, especially in a system having large planets at high orbital eccentricity.^[25]

The need for stable orbits rules out stars with systems of planets that contain large planets with orbits close to the host star (called "hot Jupiters"). It is believed that hot Jupiters formed much further from their parent stars than they are now (see planetary migration), and have migrated inwards to their current orbits. In the process, they would have catastrophically disrupted the orbits of any planets in the habitable zone.^[26] To exacerbate matters, Hot Jupiters are much more common orbiting F and G class stars.^[27]

A terrestrial planet of the right size[edit]

 

Planets of the Solar System to scale. Rare Earth argues that complex life cannot exist on large gaseous planets like Jupiter and Saturn (top row) or Uranus and Neptune (top middle) or smaller planets such as Mars and Mercury

It is argued that life requires terrestrial planets like Earth and as gas giants lack such a surface, that complex life cannot arise there.^[28]

A planet that is too small cannot hold much of an atmosphere. Hence the surface temperature becomes more variable and the average temperature drops. Substantial and long-lasting oceans become impossible. A small planet will also tend to have a rough surface, with large mountains and deep canyons. The core will cool faster, and plate tectonics will either not last as long as they would on a larger planet or may not occur at all. A planet that is too large will retain too much of its atmosphere and will be like Venus. Venus is similar in size and mass to Earth, but has a surface atmosphere pressure that is 92 times that of Earth's. Venus mean surface temperature is 735 K (462 °C; 863 °F) making Venus the hottest planet in the Solar System. Earth had a similar early atmosphere to Venus, but lost it in the giant impact event.^[29]

With plate tectonics[edit]

 

The Great American Interchange on Earth, around ~ 3.5 to 3 Ma, an example of species competition, resulting from continental plate interaction

 

An artist's rendering of the structure of Earth's magnetic field-magnetosphere that protects Earth's life from solar radiation. 1) Bow shock. 2) Magnetosheath. 3) Magnetopause. 4) Magnetosphere. 5) Northern tail lobe. 6) Southern tail lobe. 7) Plasmasphere.

Rare Earth proponents argue that plate tectonics and a large magnetic field are essential for the emergence and sustenance of complex life.^[30] Ward and Brownlee assert that biodiversity, global temperature regulation, the carbon cycle, and the magnetic field of the Earth that make it habitable for complex terrestrial life all depend on plate tectonics.^[31]

Ward and Brownlee contend that the lack of mountain chains elsewhere in the Solar System is direct evidence that Earth is the only body with plate tectonics and as such the only body capable of supporting life.^[32]

Plate tectonics is dependent on chemical composition and a long-lasting source of heat in the form of radioactive decay occurring deep in the planet's interior. Continents must also be made up of less dense felsic rocks that "float" on underlying denser mafic rock. Taylor^[33] emphasizes that subduction zones (an essential part of plate tectonics) require the lubricating action of ample water; on Earth, such zones exist only at the bottom of oceans.

Ward and Brownlee and others such as Tilman Spohn of the German Space Research Centre Institute of Planetary Research^[34] argue that plate tectonics provides a means of biochemical cycling which promotes complex life on Earth and that water is required to lubricate planetary plates.

Plate tectonics and as a result continental drift and the creation of separate land masses would create diversified ecosystems which is thought to have promoted the diversification of species, and that diversity is one of the strongest defences against extinction.^[35]

An example of species diversification and later competition on Earth's continents is the Great American Interchange. This was the result of the tectonically induced connection between North and Middle America with the South American continent, at around 3.5 to 3 Ma. The previously undisturbed fauna of South America could evolve in their own way for about 30 million years, since Antarctica separated. Many species were subsequently wiped out in mainly South America by competing Northern American animals.

A large moon[edit]

 

Tide pools resulting from tidal interaction of the Moon are said to have promoted the evolution of complex life.

The Moon is unusual because the other rocky planets in the Solar System either have no satellites (Mercury and Venus), or have tiny satellites that are probably captured asteroids (Mars).

The giant impact theory hypothesizes that the Moon resulted from the impact of a Mars-sized body, Theia, with the very young Earth. This giant impact also gave the Earth its axial tilt and velocity of rotation.^[33] Rapid rotation reduces the daily variation in temperature and makes photosynthesis viable.^[36] The Rare Earth hypothesis further argues that the axial tilt cannot be too large or too small (relative to the orbital plane). A planet with a large tilt (inclination) will experience extreme seasonal variations in climate, unfriendly to complex life. A planet with little or no tilt will lack the stimulus to evolution that climate variation provides.^{[citation needed]} In this view, the Earth's tilt is "just right". The gravity of a large satellite also stabilizes the planet's tilt; without this effect the variation in tilt would be chaotic, probably making complex life forms on land impossible.^[37]

If the Earth had no Moon, the ocean tides resulting solely from the Sun's gravity would be only half that of the lunar tides. A large satellite gives rise to tidal pools, which may be essential for the formation of complex life, though this is far from certain.^[38]

A large satellite also increases the likelihood of plate tectonics through the effect of tidal forces on the planet's crust.^{[citation needed]} The impact that formed the Moon may also have initiated plate tectonics, without which the continental crust would cover the entire planet, leaving no room for oceanic crust.^{[citation needed]} It is possible that the large scale mantle convection needed to drive plate tectonics could not have emerged in the absence of crustal inhomogeneity.

If a giant impact is the only way for a rocky inner planet to acquire a large satellite, any planet in the circumstellar habitable zone will need to form as a double planet in order that there be an impacting object sufficiently massive to give rise in due course to a large satellite.^{[citation needed]}

 

Earth's atmosphere

Atmosphere[edit]

A terrestrial planet of the right size is needed to retain an atmosphere, like Earth and Venus. On Earth, once the giant impact of Theia thinned Earth's Atmosphere other events were needed to make the atmosphere capable of sustaining life for a long time span. On Earth the Late Heavy Bombardment reseeded Earth with water lost after the impact of Theia.^[39] The development of an ozone layer formed protection from ultraviolet (UV) radiation from the Sun.^[40][41] Nitrogen and carbon dioxide are needed in a correct ratio for life to form. Nitrogen is needed for amino and nucleic acids.^[42] Lightning is needed for nitrogen fixation to happen.^[43][43] The carbon dioxide gas needed for life comes from sources such as volcanoes and geysers. Carbon dioxide is only needed at low levels^{[citation needed]}, in Earth's atmosphere it is at 0.04 percent (400 ppm) by volume of the atmosphere. At high levels carbon dioxide is poisonous.^[44][45] Precipitation is needed to have a stable water cycle.^[46] A proper atmosphere must reduce temperature extremes between day and night (the diurnal temperature variation).^[47][48]

One or more evolutionary triggers for complex life[edit]

 

This diagram illustrates the twofold cost of sex. If each individual were to contribute to the same number of offspring (two), (a) the sexual population remains the same size each generation, where the (b) asexual population doubles in size each generation

Regardless of whether planets with similar physical attributes to the Earth are rare or not, some argue that life usually remains simple bacteria. Biochemist Nick Lane argues that simple cells (prokaryotes) emerged soon after Earth's formation, but since almost half the planet's life had passed before they evolved into complex ones (eukaryotes) all of whom share a common ancestor, this event can only have happened once. In some views, prokaryotes lack the cellular architecture to evolve into eukaryotes because a bacterium expanded up to eukaryotic proportions would have tens of thousands of times less energy available; two billion years ago, one simple cell incorporated itself into another, multiplied, and evolved into mitochondria that supplied the vast increase in available energy that enabled the evolution of complex life. If this incorporation occurred only once in four billion years or is otherwise unlikely, then life on most planets remains simple.^[49] An alternative view is that mitochondria evolution was environmentally triggered, and that mitochondria-containing organisms appear very soon after first traces of oxygen appear in Earth's atmosphere.^[50]

The evolution of sexual reproduction as well as its maintenance, is another mystery in biology. The purpose of sexual reproduction is unclear, as in many organisms it has a 50% cost (fitness disadvantage) in relation to asexual reproduction.^[51] Mating types (types of gametes, according to their compatibility) may have arisen as a result of anisogamy (gamete dimorphism), or the male and female genders may have evolved before anisogamy.^[52][53] It is also unknown why most sexual organisms use a binary mating system,^[54] and why some organisms have gamete dimorphism. Charles Darwin was the first to suggest that sexual selection drives speciation (the formation of species); without sexual reproduction it is unlikely that complex life would have evolved.

The right time in evolution[edit]

 

Timeline of evolution; human writings exists for only 0.000218% of Earth's history.

While life on Earth is regarded to have spawned relatively early in the planet's history, the evolution from multicellular to intelligent organisms took around 800 million years.^[55] Civilizations on Earth have existed for about 12,000 years and radio communication reaching space has existed for less than 100 years. Relative to the age of the Solar System (~4.57 Ga) this is a tiny age span, an age span in which extreme climatic variations, super volcanoes or large meteorite impacts were absent. These events would severely harm intelligent life, as well as life in general. For example, the Permian-Triassic mass extinction, caused by widespread and continuous volcanic eruptions in an area the size of Western Europe, led to the extinction of 95% of known species around 251.2 Ma ago. About 65 million years ago, the Chicxulub impact at the Cretaceous–Paleogene boundary (~65.5 Ma) on the Yucatán peninsula in Mexico led to a mass extinction of the most advanced species at that time.

If intelligent extraterrestrial civilizations did exist and with such an intelligence level that they could make contact with distant Earth, they would have to live in the same time span in evolution. The nearest Earth-like planets are around 4.2 light years away; probable planets as Proxima Centauri b around the star Proxima Centauri, a star considered to be 4.65 Ga; 0.15 billion years older than the Sun.

Under the assumption that both the explosion of life and the development of civilization were to be relative to the planet's age, they would have spawned 723 Ma and 12.691 ka, respectively. The time between the life explosion if that had existed on an exoplanet and the dawn of civilizations is thus very large and the time between civilization and radio signals evenly so.

The risk of intelligent-life destruction is not a Drake equation factor; in the 33 million years since the Eocene-Oligocene extinction event there have been no major mass extinctions.

The chance of bigger impacts in the time span of evolution to intelligent life depends on the amount of shielding by larger bodies, such as our system's Jupiter or the Moon. The chance of a large impact and resulting mass extinctionhappening in a multi-planetary "protected" system is, however, impossible to predict.

 

 

 

[Legend_in_blue]

Saw this one earlier last week...

 

 

Can't say I believe this stuff