Marduk

I read where the drag of the moon will slow the rotation of the Earth till one day will equal one lunar month in a few hundred thousand years, what effect 14 days of darkness followed by 14 days of sunlight will do to the Earth I'm not sure. Krauss was the name of the Physicist that wrote it.

Feather

Links, please? I don't believe the moon has that much influence over the earth. But I've never worked it out, so I could very well be wrong. It would be interesting to see the physics behind this hypothesis.

Jesse

Craig:
That number seems awfully low to me, 100 million years is not long at all. Is there some graph showing why they picked that number, that shows the rate of change of the CO2 level?

Well, here's an article that shows a graph of CO2 levels in the past, although it doesn't extrapolate them into the future:

http://calspace.ucsd.edu/virtualmuse...ge2/07_1.shtml

Here are some other articles which talk about a recent estimate by a scientist named John Kasting about how long until CO2 levels become to low for plants (refining an earlier estimate by James Lovelock, inventor of the 'Gaia hypothesis'), although they don't go into a lot of detail on how the estimates were made..it has something to do with the fact that more heat from the sun means silicate rocks will absorb more CO2, apparently.

http://abcnews.go.com/sections/scien...ate000220.html
http://www.spaceref.com/news/viewpr.html?pid=908
http://www.recyclingpoint.com.sg/Art...thisdoomed.htm

Craig

I'll have to look closer at these when I have more time. Thanks.

Marduk

"Links, please? "

No link, it was one of his books (Lawrence Krauss) 'The Physics of Star Trek' or 'Beyond Star Trek'. I think the latter.

Silent Acorns

I'm a bit unconfortable with this idea.

1) As long as the Earth's temperature stays below 100 C, the earth won't get much drier since any water that leaves the oceans by evapourating must enter the atmosphere and eventually condence somewhere.

2) The ice caps will melt and increase the total amount of fluid water in the hydrologic cycle.

3) The example of Venus shows that high carbon dioxide levels can coexist with high temperatures very nicely.

Where is all the CO2 and H20 supposed to go? Into the rocks? Outer space? Or are we talking about an atmosphere warmer than 100 C?

Friar Bellows

As the Earth warms up, the oceans evaporate and the atmosphere becomes moister. Rainfall increases. This increases the rate of (silicate rock) weathering. Carbon dioxide can be removed from the atmosphere by these weathering rocks (via chemical reactions), and then ultimately it finds it way into the oceans (in the form of calcium carbonate). If weathering can remove carbon dioxide from the atmosphere quicker than it is released back into the atmosphere (e.g. by volcanism), then there is a net decrease of carbon dioxide from the atmosphere. This can happen when the rainfall (and hence the rate of weathering) is high enough.

Now for water. At a global average temperature of 60°C water becomes a major component of the atmosphere. Much of this water finds it way to the stratisphere, where it is broken down by UV light into hydrogen and oxygen, and the hydrogen then escapes into space. Ultimately this process leads to the loss of our oceans.

Note that carbon dioxide may find it way back into the atmosphere after the oceans have dried out. Or even before that, but after the plants have died out.

I think this answers most of your points, but probably raises even more questions, probably none of which I can answer!

Answerer

Guys, I think all of you had missed out a possibility of an asteroid impact.

Friar Bellows

Good catch! I would add a nearby supernova and perhaps an extremely intense, widespread and sustained period of volcanism to the list.

lpetrich

First, the Earth won't be dragged to Moon-synchronous rotation in only a few hundred thousand years. A few billion maybe, but not a few hundred thousand -- the Earth is not spinning down that fast.

Also, what Friar Bellows describes is a sort of geochemical thermostat.

Higher temperature ->
more water evaporated ->
more weathering ->
more CO2 consumed by weathering rocks ->
less CO2 in the atmosphere ->
less greenhouse effect ->
lower temperature.

This may explain why the Earth has had liquid water for nearly 4 billion years, despite the Sun's slow brightening; the Earth had had more CO2 and other greenhouse gases in the past, keeping it warm enough to allow those greenhouse gases to be consumed by weathering.

But as the Sun gets hotter, less and less CO2 is necessary for maintaining equilibrium, and eventually the thermostat gets broken, with the Earth getting hotter and hotter.

This causes trouble for plants, since they need to fix CO2. But I'm not sure that most present-day plants' descendants will be doomed in 100 million years -- I'm sure that some of them will evolve greater CO2-fixing efficiency as C4 plants have already done. So it won't exclusively be tropical grasses populating the Earth in that time.

But there will eventually be a limit to CO2-fixing capability -- if it takes too much energy to do that, the plants will grow very slowly, and ultimately not at all.

Also, as the Earth heats up, much of life could well go extinct before the Earth's water's hydrogen evaporates into outer space. Consider these temperature limits (from this source):

Fish: 38 C
Insects: 45-50 C
Ostracods: 49-50 C

Vascular Plants: 45 C
Mosses: 50 C

Protozoa: 56 C
Algae: 55-60 C
Fungi: 60 C

Cyanobacteria: 70-73 C
Other photosynthetic bacteria: 70-73 C
Organic-material-eating bacteria: 90 C

Methanogens: 110 C
Sulfur-using archaea: 115 C

The more complex an organism is, the lower its maximum temperature is, most likely due to the interdependence of all its molecular mechanisms. However, with enough time and with the whole planet being heated, there may be some complex organisms pushing beyond their current upper limits.