End Of Life On Earth Scenarios

[steve_bank]

Future of Earth - Wikipedia

en.wikipedia.org

The biological and geological future of Earth can be extrapolated based on the estimated effects of several long-term influences. These include the chemistry at Earth's surface, the cooling rate of the planet's interior, gravitational interactions with other objects in the Solar System, and a steady increase in the Sun's luminosity. An uncertain factor is the influence of human technology such as climate engineering,[2] which could cause significant changes to the planet.[3][4] For example, the current Holocene extinction[5] is being caused by technology,[6] and the effects may last for up to five million years.[7] In turn, technology may result in the extinction of humanity, leaving the planet to gradually return to a slower evolutionary pace resulting solely from long-term natural processes.[8][9]

Over time intervals of hundreds of millions of years, random celestial events pose a global risk to the biosphere, which can result in mass extinctions. These include impacts by comets or asteroids and the possibility of a near-Earth supernova—a massive stellar explosion within a 100-light-year (31-parsec) radius of the Sun. Other large-scale geological events are more predictable. Milankovitch's theory predicts that the planet will continue to undergo glacial periods at least until the Quaternary glaciation comes to an end. These periods are caused by the variations in eccentricity, axial tilt, and precession of Earth's orbit.[10] As part of the ongoing supercontinent cycle, plate tectonics will probably create a supercontinent in 250–350 million years. Sometime in the next 1.5–4.5 billion years, Earth's axial tilt may begin to undergo chaotic variations, with changes in the axial tilt of up to 90°.[11]

The luminosity of the Sun will steadily increase, causing a rise in the solar radiation reaching Earth and resulting in a higher rate of weathering of silicate minerals. This will affect the carbonate–silicate cycle, which will reduce the level of carbon dioxide in the atmosphere. In about 600 million years from now, the level of carbon dioxide will fall below the level needed to sustain C3 carbon fixation photosynthesis used by trees. Some plants use the C4 carbon fixation method to persist at carbon dioxide concentrations as low as ten parts per million. However, in the long term, plants will likely die off altogether. The extinction of plants would cause the demise of almost all animal life since plants are the base of much of the animal food chain.[12][13]

In about one billion years, solar luminosity will be 10% higher, causing the atmosphere to become a "moist greenhouse", resulting in a runaway evaporation of the oceans. As a likely consequence, plate tectonics and the entire carbon cycle will end.[14] Then, in about 2–3 billion years, the planet's magnetic dynamo may cease, causing the magnetosphere to decay, leading to an accelerated loss of volatiles from the outer atmosphere. Four billion years from now, the increase in Earth's surface temperature will cause a runaway greenhouse effect, creating conditions more extreme than present-day Venus and heating Earth's surface enough to melt it. By that point, all life on Earth will be extinct.[15][16] Finally, the planet will likely be absorbed by the Sun in about 7.5 billion years, after the star has entered the red giant phase and expanded beyond the planet's current orbit.[17]

There is a 1% chance every billion years that a star will pass within 100 AU of the Sun, potentially disrupting the Solar System.[29] The mean time for the Sun to collide with another star in the solar neighborhood is approximately 30 trillion (3×1013) years, which is much longer than the estimated age of the Universe, at approximately 13.8 billion years. This can be taken as an indication of the low likelihood of such an event occurring during the lifetime of the Earth.[30] Based on results from the Gaia telescope's second data release from April 2018, an estimated 694 stars will approach the Solar System to less than 5 parsecs in the next 15 million years. Of these, 26 have a good probability to come within 1.0 parsec (3.3 light-years) and 7 within 0.5 parsecs (1.6 light-years).[31]

 

[lpetrich]

The Earth has had liquid water for over 4 billion years, even though the Sun gradually grew brighter over this time, from around 75% present luminosity 4 billion years ago:  Faint young Sun paradox The Earth's current average surface temperature is around 15 C, and extrapolating backward with the Stefan-Boltzmann law gives -5 C back then.

 Carbonate–silicate cycle - it has been a geochemical thermostat for the last 4 billion years. Here is how it works:

Volcanoes spew out CO2, and that increases the atmosphere's greenhouse effect. That makes the Earth's surface warmer, and that increases weathering of rocks. This weathering absorbs CO2, reducing the greenhouse effect and making the Earth cooler.

Let's look at the history of the Earth's atmosphere's CO2 levels. Its preindustrial value is 280 ppmv (parts per million by volume) and it stayed close to that value for much of the Holocene Epoch.  Milankovitch cycles - it varies from preindustrial levels in interglacial periods to as low as 180 ppmv at maximum glaciation.

 File:Phanerozoic_Carbon_Dioxide.png - at the Cretaceous-Paleogene boundary (66 Mya), 750 ppmv, at the Jurassic-Cretaceous boundary (143 Mya), 1500 ppmv, at the Carboniferous-Permian boundary (299 Mya), 500 ppmv, in the Cambrian Period (539 - 487 Mya), 4500 ppm.

Atmospheric carbon dioxide concentrations over the past 60 million years - PubMed - at the Paleocene-Eocene boundary (56 Mya), 2000 ppmv

A 300-million-year record of atmospheric carbon dioxide from fossil plant cuticles - PubMed - for most of the Mesozoic Era (252 - 66 Mya), 1000 - 2000 ppmv

Coupling of surface temperatures and atmospheric CO2 concentrations during the Palaeozoic era - PubMed - "several times" the present level over much of the Paleozoic, declining to close to the present level in the Carboniferous Period (359 - 299 Mya).

High CO2 levels in the Proterozoic atmosphere estimated from analyses of individual microfossils - PubMed - Proterozoic: (2,500 - 539 Mya) - 10 to 200 present atmospheric levels (3,000 - 60,000 ppmv)

Atmospheric carbon dioxide concentrations before 2.2 billion years ago - PubMed (2.75 - 2.2 Gya) - less than 40,000 ppmv - other greenhouse gases like methane?

 

[lpetrich]

In summary, the amount of CO2 has been declining as the Sun has become brighter.  Future of Earth - 600 million years from now, the CO2 concentration should drop to 60 ppm. That will mean the end of  C3 carbon fixation in land plants, with only plants that do  C4 carbon fixation surviving. But perusing  List of C4 plants makes it evident that C4 processes evolved multiple times, so it's likely that C4 will evolve more times, with C3 stragglers getting squeezed out as CO2 levels drop.

C4 carbon fixation can continue until the concentration of CO2 reaches 10 ppm, which should happen around 0.8 - 1.2 billion years from now.

Around then, the CO2 thermostat will run out, and the Earth's surface will lose that constraint on its temperature. One billion years from now, the Sun will be 1.1 times as bright as at the present, and if the Earth's average surface temperature is still 15 C, then its extrapolated present value will be 8 C. According to  Planetary equilibrium temperature the average temperature for the Moon is around -2 C, and that scales up to 5 C at this solar luminosity.

 

[lpetrich]

Starting at around one billion years from now, the carbon-silicon thermostat will fail, and the Earth will gradually get warmer. This will make the atmosphere have more and more water vapor, adding to its greenhouse effect. How will this work out in detail? The evolution of habitable climates under the brightening Sun -- Journal of Geophysical Research: Atmospheres

Note: this simulation used the present-day level of carbon dioxide. By a billion years from now, there will be much less, and I will attempt to adjust their results for that.

They find that with a solar flux of 10% above present (adjusted: 20% above present, 2 billion years from now), the Earth's average temperature is 35 C (present: 15 C). Then it speeds up, slowing down again at 15% above present (25%, 2.5 billion years), with a temperature of 65 C. At 20% above present (30%, 3 billion years from now), the average temperature will be 90 C.

This simulation did not address CO2 levels, which would decline, and then increase, as the Earth's freshwater becomes too warm to dissolve much CO2, and eventually disappears altogether. Volcanoes will still be releasing CO2, and carbonate rocks might have their CO2 baked out of them. That will add to the greenhouse effect, making the Earth warm faster.

Another effect is photodissociation of H2O in the upper atmosphere, with the released hydrogen escaping into space. As our planet warms, more and more water vapor will get up there, and more and more will break apart. So our planet will become like Venus, with most of its former water gone, as is evident from its hydrogen-isotope mixture. Venus's deuterium fraction is some 100 times more than the Earth's.

 

[lpetrich]

Now for temperature tolerance.

For our species, it is some 40 - 50 C - How hot is too hot for the human body? Study identifies upper limit

The thermal limits to life on Earth | International Journal of Astrobiology | Cambridge Core

At the very highest temperatures only archaea are found with the current high-temperature limit for growth being 122 °C. Bacteria can grow up to 100 °C, but no eukaryote appears to be able to complete its life cycle above ∼60 °C and most not above 40 °C.

40 C = 104 F, 50 C = 122 F, 60 C = 140 F, 100 C = 212 F, 122 C = 252 F

An odd issue is why are so few organisms adapted for extreme conditions? Why not more? Are there things that are just plain difficult to evolve?

Above 40 C, most eukaryotes will likely be gone, with the stragglers gone by 60 C, leaving prokaryotes.

Among these, a few cyanobacteria can survive at higher temperatures, and above 75 C, they also will be gone. Evolution of Thermotolerance in Hot Spring Cyanobacteria of the Genus Synechococcus - PMC

That means no oxygen-releasing photosynthesis above that temperature, and likely none of *any* photosynthesis. Above it, autotrophic organisms get their energy from chemical reactions, like, for instance, methanogens, which do

CO2 + 4H2 -> CH4 + 2H2O

The champion in temperature tolerance is  Methanopyrus kandleri, which can grow at 122 C. It is a methanogen.

So the last organisms on our planet will likely be super temperature tolerant methanogens and the like.

 

[lpetrich]

So our planet will go through a phase where much of our atmosphere will be water vapor. Even so, most ocean water will still stay in place, will stay liquid, until the temperature becomes *very* high.

This is because of water vapor pressure, something that increases with temperature. It lowers water's boiling point at high altitudes, making it take longer to boil an egg at high altitudes. It also makes a  Pressure cooker good, enabling cooking in water above 100 C.

Water Vapor Saturation Pressure: Data, Tables & Calculator at the Engineering Toolbox, Boiling Point at Altitude Calculator and Water - Boiling Points vs. Altitude at the ET, 1976 Standard Atmosphere Calculator at Digital Dutch, Water phase diagram at "Water Structure and Science", and  Phases of ice

Selected temperatures and their water vapor pressures in bars (sea-level pressure = 1.013 bar, 1 bar = 100 kilopascals). The pressure of 10 meters of ocean water is about 1 bar, so 1 kilometer of depth gives 100 bars, so it will indicate how much ocean has been stripped off from the heat.

• 15 C - 0.017 b - 1.7 cm
• 35 C - 0.057 b - 5.7 cm
• 65 C - 0.25 b - 2.5 m
• 100 C - 1 b - 10 m
• 122 C - 2.1 b - 21 m
• 370 C - 210 b - 2.1 km - critical point of water

So when the last organism is driven into extinction, one like Methanopyrus kandleri, most of the ocean water will still be in place, unless most of the Earth's surface water was dissociated in the upper atmosphere.

The critical point of water has the maximum temperature where there is a distinction between liquid and gaseous water -- above that point, water fades from gaseous to liquid.

 

[lpetrich]

As the Earth becomes intolerably hot, will the poles be refuges?

Four cases:

• Moon: equator max 121 C, min -133 C; permanently shaded: < 246 C
• Mars: equator max 20 C, min -70 C; poles -153 C
• Earth:
  • Equatorial oceanic (São Tomé, 0d): max 29 C (27 C, 29 C, 34 C), min 22 C (23 C, 20 C,13 C)
  • Equatorial continental (Manaus, 4d): max 32 C (31 C, 34 C, 38 C), min 24 C (25 C, 24 C, 12 C)
  • Low-latitude oceanic (Honolulu, 21d): max 29 C (27 C, 32 C, 35 C), min 22 C (24 C, 19 C, 11 C)
  • Low-latitude continental (Riyadh, 24d) max 33 C, (20 C, 43 C, 49 C), min 18 C (30 C, 8 C, -5 C)
  • High-atitude oceanic (Reykjavík, 64d) max 8 C (3 C, 15 C, 26 C), min 3 C (9 C, -2 C, -24 C)
  • High-latitude continental (Yellowknife, 62d) max 0 C (-22 C, 22 C, 33 C), min -8 C (13 C, -29 C, -51 C)
  • Polar continental (South Pole, 90d) mean summer -28 C, mean overall -50 C, mean winter -60 C
• Venus: very little variation around 464 C

Daily variation:

• Moon equator: 254 C
• Mars equator: 90 C
• Earth: EqO 6 C, EqC 8 C, LLO 8 C, LLC 12 C, HLO 6 C, HLC 8 C.
• Venus: a few C

Though our planet does not have much daily variation, it does has sizable latitude variation, and oceans damp out a lot of seasonal variation.

I suspect that the poles will likely be refuges if the greenhouse effect is not too strong and if there is continent at them.

 

[steve_bank]

For years there have been lengthy debates on philosophy forum over determinism.


For physical science the question is how would you prove a deterministic universe by experiment? I do not think it can be done.

The electron is unitized partial of electric charge. Put a chree on a cactor and tere are an integer number of electrons on the capacitor. Measurement wise we treat charge on a c[-ator as a continuum because the discretization is well below measurement caopcity.
Infinity divisible real numbers.

Same with ass in kilograms, meters in kilometers and time in seconds.


As to QM or any theory the validation of a model is in predictive results.

We are limited by our measurement instrumentaion and quantitation nose, the discrete nature of QM.

If a revision to QM makes it reflect a deterministic inverse, then QM should be able to predict excellently where a particle will hit an XY target in a slit diffraction experime4nt.

QM shud be able to rect exactly when urnium will eit a [rtcle and the direction.

QM should be able to predict the exact amplitude of electrical noise at a point in time.

Same issue with string theory

String Theory
Partly because of theoretical and mathematical difficulties and partly because of the extremely high energies needed to test these theories experimentally, there is so far no experimental evidence that would unambiguously point to any of these models being a correct fundamental description of nature.

 

[SLD]

The Earth has had liquid water for over 4 billion years, even though the Sun gradually grew brighter over this time, from around 75% present luminosity 4 billion years ago:  Faint young Sun paradox The Earth's current average surface temperature is around 15 C, and extrapolating backward with the Stefan-Boltzmann law gives -5 C back then.

So I had always wondered about the faint young sun paradox, and so read the Wikipedia entry on it. Mostly seems to discuss possible greenhouse gasses. But I had always thought that the young earth was hotter for two reasons. One, geothermal issues, I.e., it just took a helluva long time for the earth to cool down from the Hadean period. During that time, liquid water formed and voila life took hold. Second was radioactive decay. While that is not generally hospitable to life, we are only bacteria at this point in time.

But I’ve never seen any calculations about how long it should take he earth to cool down after it solidified from a basically molten state. Or exactly how much radioactivity contributed to the earth’s temperature, other than it was supposedly significant.

I would also have thought that the earth was more volcanically active earlier in its history because the crust was still forming and therefore not as thick as it is now. But I’m not sure.

 

[bilby]

Second was radioactive decay. While that is not generally hospitable to life, we are only bacteria at this point in time.

Water is an excellent barrier against radiation.

https://what-if.xkcd.com/29/

Yet outside the outer boundary, you could swim around as long as you wanted—the dose from the core would be less than the normal background dose you get walking around. In fact, as long as you were underwater, you would be shielded from most of that normal background dose. You may actually receive a lower dose of radiation treading water in a spent fuel pool than walking around on the street.

...

So, as far as swimming safety goes, the bottom line is that you’d probably be ok, as long as you didn’t dive to the bottom or pick up anything strange.

But just to be sure, I got in touch with a friend of mine who works at a research reactor, and asked him what he thought would happen to you if you tried to swim in their radiation containment pool.

“In our reactor?” He thought about it for a moment. “You’d die pretty quickly, before reaching the water, from gunshot wounds.”