Comments on: Earth, Barely Habitable?

By: bonus

bonus — Sat, 13 Sep 2008 10:21:28 +0000

Please read the thread on this site "Mars once had plate tectonics". Obviously, it ceased due to Mars cooling, but it was there once, and when Earth cool, its plate tectonics will cease, too. In other words, Earth is NOT on any "borderline of habitability"

By: Charles Peter Watson

Charles Peter Watson — Sat, 29 Mar 2008 21:08:34 +0000

With the consideration that plate tectonics, being only a theory at present, the siesmic shifts caused by them have also contributed to the emission of dangerous sulfuric gases that have altered climatic conditions on Earth (Pinatubo, Krakatoa). The 2004 Indonesian earthquake not only spawn one of the deadliest tsunamis but lost Earth a miniscule fraction of its rotation time, shortening the average day but not by a recognizable amount.
As for habitability, planet mass is not so much a factor as is its core size where the molten rock that fuels the tectonics & thus the continental drifts are churned by their own volitility as well as planetary rotation. It should also be noted that there is a timline to the cooling period of that core & there will be no more movement of the crust. Despite this occurance being in the very, very extreme future, can Earth life be spared on a planetary mass of whatever exponential size without tectonic activity should human successfully colonize the Moon prior to Mars?

By: Joe

Joe — Mon, 11 Feb 2008 20:37:00 +0000

An interesting though would be the life-span of the creatures that spawn from this planet. And perhaps the rate they experience life. That would have to do with the span of one cycle of the planets season (if it has a cycle of seasons). Could it be that if the mere rotation of a planet had anything to do with the life-span of the creatures that lived upon it?

By: Lyle

Lyle — Sat, 12 Jan 2008 04:48:16 +0000

Lol, … methinks we're applying base premises that correlate to 'Earth' rather than the 'reality' of a hypothetical planet of different properties, … such as plate tectonics or not.

Good point Greg about 'proportionality' and distance, … most people miss that one.

A 'slower' carbon cycle does not exclude other carbon cycles.

By: RUF

RUF — Sat, 12 Jan 2008 04:33:01 +0000

Terra-forming Mars is not possible, as Mars has no magnetic field. any atmosphere (including the nitrogen-oxygen atmosphere that we need) would be stripped away to space by solar wind. Time to put this whole terra-forming Mars idea to rest…

By: Kevin M.

Kevin M. — Fri, 11 Jan 2008 02:24:07 +0000

Earth barely habitable – perhaps, but it still sounds like we're on the much calmer and nicer edge of habitability. More tectonics means far more violent catastrophes all the time, kind of like the Woody Allen movie where his childhood home was situated underneath a roller coaster.

Plus, there is the interesting question of whether more rapid concentration of life forms on a smaller smaller surface area leads to faster cultural and therefore mental development? Wider surface – slower mixing and interacting of distant cultures?

Also, if birds are heavier, but the atmosphere is thicker, does that mean that they fly just as well? Does everything move slower and slithery-er, not much jumping around? I admit I'm afraid to meet the intelligent ones.

By: Kevin M.

Kevin M. — Fri, 11 Jan 2008 02:05:39 +0000

Very interesting thoughts. By "smaller", I assume you mean "less tall", but not necessarily, if it is really tall and thin or flat and wider. This in no way means that there would be fewer life forms, just very different ways of living together. Life finds a way, I'm sure in ways that we cannot imagine yet. It is time that someone made up a simulator algorythm for biological life forms under different gravities and pressures.

By the way, does any of this imply how Venus or Mars could yet be terraformed, though without tectonics? It seems very do-able in a few lifetimes that we could harness such energies and deliver or manufacture water and gases on both planets. Without tectonics, it sounds like it might take direct intervention of materials. Even if they didn't become habitable for a while, it would be utterly fascinating to see what effects it would have. Talk about a laboratory! It must be done.

By: mansie

mansie — Thu, 10 Jan 2008 18:56:13 +0000

I imagine that life-forms on a higher G planet would be smaller. As would trees, mountains and the general terrain. The atmosphere would be far thicker, as would atmospheric pressure – not sure what effect this might have on flying animals, aeroplanes and space launches…

Interesting to speculate though!

By: Mark

Mark — Thu, 10 Jan 2008 16:26:32 +0000

I did some rough calculations, and assuming that the density remains the same, a planet with 10x Earth's mass will have roughly 2x the radius. g at the surface works out to 21.16 m/s/s. One would then experience 2.15x his/her regular weight.
This is, of course, assuming that I know what I'm doing.

By: Pedro

Pedro — Thu, 10 Jan 2008 10:29:25 +0000

Life spreading like in a paradise in a planet as much as 10 times earth mass? Even though Greg says that gravity of sych planet isn't a direct proportion, we could expect something around 6 or 7 times earth gravity, wouldn't we? So, what sort of life would thrive with such weigh? I read somehere that as litle as 2-2,5 times our gravity was too much to non-water complex life forms developed. This would mainly influence carbon life forms with circulatory sistems like every mammals, wouldn't so?

By: Greg

Greg — Thu, 10 Jan 2008 07:59:39 +0000

The problem with Venus is a matter of balancing extremes. Earth sequesters alot of its carbon dioxide which cools it down. At some point Earth was cool enough to form liquid water which is a necessary ingredient to form minerals rocks with carbon dioxide that pulls it out of the atmosphere. Over time plate tectonics has melted these minerals which releases enough of carbon dioxide back into the atmosphere (via volcanoes) to keep Earth from freezing over. A simple way to think of it is that water is trying to cool the planet into a snowball while plate tecotnics is trying to warm it up with volcanoes. Venus underwent a runaway greenhouse event where too much carbon dioxide was released into the atmosphere warming it up so much that it became too hot for water to exist. The water evaporated and due to the atmosphere being full of carbon dioxide the water vapor leeched away into deep space rather than falling as rain like on Earth. Without water the carbon dioxide does not get pulled out of the atmosphere via rock formation with water. Venus now inescapably hot as Hades a result.

By: Greg

Greg — Thu, 10 Jan 2008 07:40:08 +0000

The size or diameter of a planet does not necessarily reflect it's mass, depending on it's composition and density of heavier elements. If in fact the planet had 10 times the mass as Earth, you would "weigh" 10 x as much if you were the same distance from the center of that planet as you are from the center of the Earth. Since the diameter of the larger mass planet will also be much larger, you would likely be farther from the center of gravity and not weigh so much there. Since gravity decreases at the square of the distance from the center of an object, you would need to crunch some numbers to figure out your weight on the surface of any such object. Suffice it to say your weight will be greater,but not in direct proportion to the greater mass of the planet.

By: Khyron

Khyron — Wed, 09 Jan 2008 21:03:02 +0000

These claims are hard to reconcile with the fact that Venus, where plate tectonics are lacking, has a huge abundance of carbon dioxide in the atmosphere. In fact, the explanation I recall for Venus' CO2 quantities is the lack of a tectonic carbon cycle, the opposite of the effect claimed here.

Perhaps this study still assumed an oversized moon to strip away most of the atmosphere, thus requiring atmospheric CO2 replenishment?

By: Fraser Cain

Fraser Cain — Wed, 09 Jan 2008 20:17:22 +0000

No, that was poorly worded, you're right. I fixed it.

By: orkstrtdkaos

orkstrtdkaos — Wed, 09 Jan 2008 19:59:02 +0000

You are correct in thinking that you'd weigh 3 times as much. But if you understand the quoted statement to mean that weight is an "experience" of mass… then the statement is true. We would "experience" what it would be like, gravitationally, if we had 3 times the mass.

By: alastair

alastair — Wed, 09 Jan 2008 18:21:32 +0000

"We'd experience 3 times the mass"?!!

Are you sure about that statement? Don't you mean "weight"?