Human Survival

[Anomalocaris]

I clearly state that they evolved into new species.

Evolving into new species does not make the old species not extinct. Duh

[Rahul]

Evolving into new species does not make the old species not extinct. Duh

But it does show that they didn't all die off leaving no offspring.

Duh.

[Anomalocaris]

As I said it depends on who you talk to, but as far as greenhouse affects on Earth it is my understanding the sooner rather than later crowd believes the problem here in the distant future is expected to be water vapor as opposed to carbon dioxide. Initial heating due to more energy from the sun, possibly in combination with anthropogenic and other greenhouse gasses, raise the level of water vapor in the atmosphere and cause further heating. Eventually the water vapor vapor will be lost into space but not before it heats the place up more than the current ecosystem can bear.

Who knows though? Maybe by that time we will have the ability to move our planet to a bigger orbit. If we haven't gone the way of the dodo already.

The question is whether the water vapor greenhouse would make the entire surface of the earth too hot for complex ecosystem, or only the equatorial and maybe temporate zone too hot. Recent forecasts seem to suggest many things could constrain the water vapor green house so that higher latitudes would continue to be amenable to complex ecosystems.

[popeyespappy]

No there currently isn’t a lot of water vapor at the poles. Too cold for that. But the lack of water vapor is one of the reasons the northern latitudes are warming faster than the rest of the planet. The temperatures at high latitudes are driven more by albedo and trace gasses other than water vapor. Mostly albedo. Since these things are a larger component of the temperature changes to both cause a larger effect there than the same change would in areas with higher water vapor content.

In any case as the rest of the planet warms ice cover will be lost at the poles. As the ice melts the temperature will increase and the atmosphere will hold more water vapor. It isn’t long (geologically speaking) before that positive feedback overcomes lower energy, and the poles reach an average annual temperature above zero degrees C. At that point all bets are off.

But your point is interesting, and I hadn’t read that before. I would be interested in some links if you have any. I looked but didn’t have much luck finding anything.

[Anomalocaris]

The point isn't there is not enough water vapor in the atmosphere near the poles now. The point is even a future global water vapor green house will not be able to elevate the temperature in high latitudes near the point where complex ecosystem can no longer survive. The temperature threshold where complex ecosystem will no longer be able to survive is often tagged at 50 degrees C. The equatorial region may average well beyond 50 degrees C in a global water vapor greenhouse, but poles will stabilize well before reaching average of 50C.

Also, even a global water vapor greenhouse would probably not lead to near total loss of water to space through photo dissociation because 2 factors. 1. The rate at which water sequestered in the mantle would be outgassed onto the surface will equilibrate the loss of water into space when there would still be quite a large amount of surface water on earth. 2. The altitude which water vapor can reach in the global water vapor greehouse scenario will decrease over time as nitrogen is removed from atmosphere through geological processes, leading to overall thinning of atmosphere, and this will lead to a gradual reduction in the efficiency of photo dissociation over time even as pace of vulcanism on earth would decrease with loss of core heat.

Recent geochemical studies suggests the mantle of the earth contains from 20-100 times more water than exists on earth's surface, chemically combined in minerals. Most of the water having been there since the formation of the earth. Only 10 years ago the estimate was mantle and lower crust contained only 1-2 times as much water as the oceans, and a good deal of that was pulled into the mantle by plate subduction.

This dramatically alters estimates of the rate at which water is release to the surface through vulcanic outgassing. It is now thought volcanic outgassing will release as much water onto the surface as is currently in all of the oceans every 1-2 billion years or so. Currently plate subduction is though to remove water from the oceans by dragging waterlogged sediments into the mantle as roughly the same rate. But plate tectonics will likely come to a stop long before vulcanism on earth comes to a stop. So the mantle is expected to become a major and damned near inexhaustable net contributor of surface water in a billion years or so.

[popeyespappy]

According to Peter Ward and Donald Brownlee it isn't going to matter even if the temperature stabilizes at the poles below 50 C. They think the atmosphere will be hostile to complex life before that point anyway due to not enough CO2 to support plant life. They think almost all atmospheric CO2 will be sequestered in the oceans long before they are gone. That's why I asked for some links. So I could look into what you are saying myself. They say that at 60 C average temperature the oceans will evaporate no matter how much water is outgassed it will evaporate and eventually be lost into space. What do your sources base the claim that the temperature will stabilize before the poles reach 50 C on? What temperature will the rest of the planet be at that point? What will the CO2 content of the atmosphere be at that point.

[Anomalocaris]

The plant dooms day clock of minus 2 hundred million years is probably set against expected time when CO2 drops below the level needed to support C3 photosynthesis used by majority of photosynthetic organisms. But there is an alternative form of photosynthesis evolved in some complex plants which can continue to function at much lower levels of CO2 concentration. So the end of complex echosystem supported oxygen respirationin multicellular life may occur much later than that.

The global average temperature during wet greenhouse:
Schröder, K.-P.; Connon Smith, Robert (May 1, 2008), "Distant future of the Sun and Earth revisited", Monthly Notices of the Royal Astronomical Society 386

The large surface water bodies supported by outgassing:
Bounama, Christine; Franck, Siegfried; von Bloh, Werner (2001), "The fate of Earth’s ocean", Hydrology and Earth System Sciences, Potsdam Institute for Climate Impact Research

Survival of complex organisms on earth beyond 2.8 billion years in the future:
O'Malley-James, J. T.; Greaves, J. S.; Raven, J. A.; Cockell, C. S., Swansong Biospheres: Refuges for life and novel microbial biospheres on terrestrial planets near the end of their habitable lifetimes

[Tonus]

Depends on who you talk to. Estimates on how long the surface of Earth can support life vary greatly. Many think the oceans will only last another 500 million to 1 billion years.

A mere three billion years before we collide with Andromeda!

[Anomalocaris]

Depends on who you talk to. Estimates on how long the surface of Earth can support life vary greatly. Many think the oceans will only last another 500 million to 1 billion years.

A mere three billion years before we collide with Andromeda!

No one thinks collision with andromeda will have much impact on the solar system besides increasingly impressive starscape in the sky.

[ManMachine]

I've been thinking recently (oh no!) about our species, and our ultimate goal to survive. I was thinking about how in the past, primitive people just survived off the scraps they found, unaware what their survival would mean for the world. We became advanced and learned how to expand, and thrive. Now, we are faced with extinction again, not from animals, starvation, disease, but from cosmic disasters, such as asteroids, supernovae and our own destruction, nukes, war, etc. I was talking to my friends recently, and they said that humans will last about 2000 years more. 2000 puny years?!?! I think we deserve more than that! We need to be AT LEAST a two planet species. If one is destroyed, the other can come back. What do you think?

We are just biologically engineered vehicles for bacteria. Sooner or later they will design one with better environmental performance, or a sunroof.

MM