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Science and Astronomy Questions
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| midtskogen | Date: Friday, 19.08.2016, 07:16 | Message # 766 |
 Star Engineer
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Norway
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| 30-40% O2 is certainly something life can adapt to, and have.
Quote Wikipedia The maximum of 35% was reached towards the end of the Carboniferous period (about 300 million years ago), a peak which may have contributed to the large size of insects and amphibians at that time.
NIL DIFFICILE VOLENTI
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| spacer | Date: Friday, 19.08.2016, 07:34 | Message # 767 |
 Star Engineer
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Israel
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| also the highest carbon dioxide in earth history was 7,000 ppm in the Cambrian period 500million years ago.
its x17 from what we have today
"we began as wanderers, and we are wanderers still"
-carl sagan
-space engine photographer
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| Banana | Date: Friday, 19.08.2016, 22:49 | Message # 768 |
 Astronaut
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United States
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| Oxygen above 30-40% would not be very safe for humans. While insects may handle that change well, humans may not. Oxygen can easily become toxic, especially at low air pressure.
Hello.
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| Watsisname | Date: Tuesday, 23.08.2016, 22:12 | Message # 769 |
 Galaxy Architect
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United States
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| Looks very promising, but I would wait a bit more.  This is an interpretation of something weird in their data, and if we are to be convinced of the interpretation it must be verified through its own predictive power. It could also just be something wrong with their experiment or analysis; they must be replicated elsewhere.
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| JackDole | Date: Tuesday, 23.08.2016, 22:55 | Message # 770 |
 Star Engineer
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Germany
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| Actually, I am surprised that no one predicted this fifth force. Or does anyone?
But if there is 'dark matter' - which seems to interact with nothing, except gravity - one might assume that there is also a 'dark force'. 
A force that interacts almost exclusively with the 'dark matter'.
If this is so, the occurrence of these particles might indicate the presence of 'dark matter'.
Don't forget to look here.
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| FastFourierTransform | Date: Wednesday, 24.08.2016, 09:57 | Message # 771 |
 Pioneer
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Spain
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| Quote Watsisname (  ) It could also just be something wrong with their experiment or analysis; they must be replicated elsewhere.
Totally agree
Quote JackDole ( ) If this is so, the occurrence of these particles might indicate the presence of 'dark matter'
In the Nature letter, the team excluded any relation to the hypothetical "Dark Force". This force has very different characteristics (and it has sub-nuclear range) if it is really a fifth force. But who knows
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| spacer | Date: Monday, 12.09.2016, 20:26 | Message # 772 |
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Star Engineer
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Israel
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| always wonder: if the sun temp was lower by 10-100kelvins.
would earth be colder in that temp range too or it wont affect at all?
"we began as wanderers, and we are wanderers still"
-carl sagan
-space engine photographer
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| Watsisname | Date: Tuesday, 13.09.2016, 00:07 | Message # 773 |
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Galaxy Architect
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| Okay, let's derive it. This is a beautiful application of geometry and physical laws.
Let the equilibrium temperature of the Earth be defined by the balance of energy in and energy out.
The energy in is the solar flux at Earth (luminosity of the Sun spread over a sphere with the size of Earth's orbit), times the cross sectional area of the Earth, times the fraction of the radiation absorbed (one minus the Earth's albedo).
The energy out follows a simple radiation law for a blackbody -- it is proportional to surface area and temperature to the 4th power, with a proportionality constant (Stefan-Boltzmann constant), and a factor for the radiative efficiency, epsilon. For the Earth, epsilon will act as a greenhouse parameter, and takes a value of about 0.6.
The luminosity of the Sun can be found in the same way.
Epsilon for the Sun is about 1 -- very close to a true blackbody.
Now relate these formulas and solve for the temperature of the Earth, obtaining
If we plug in values, this returns an equilibrium temperature of the Earth of about 289K. 255K with no greenhouse atmosphere.
Now let's see what happens if we vary the Sun's temperature. We can see the dependence is linear (4th power of sun temperature to the 1/4 power), if all else is constant.
Differentiating with respect to Sun temperature, we find that the Earth's temperature drops by 0.05 Kelvin per Kelvin that the Sun is made cooler. Which we can also figure out by simply dividing Earth's temperature by the Sun's temperature: 289/5777=0.05.
Of course, we must make a few notes. Stars don't always change temperature without also changing their radius, especially if we're comparing between different classes of stars. It's actually their luminosity that is more fundamental to determining the planet temperature. Another note is that the climate system may further respond to this change in luminosity and its equilibrium temperature, such as by changing the albedo or the greenhouse gas concentration.
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| Wicker1M | Date: Wednesday, 28.09.2016, 01:53 | Message # 774 |
 Astronaut
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| How young can a terra-type planet be to have marine unicellular life begin in it's oceans? In Space Engine, I find terras with life that are less than 1 or 2 billion years old.
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| Hornblower | Date: Wednesday, 28.09.2016, 02:23 | Message # 775 |
 World Builder
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United States
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| Do we have a date for the postponed Expedition 49 launch yet?
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| midtskogen | Date: Wednesday, 28.09.2016, 03:53 | Message # 776 |
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Star Engineer
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Norway
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| Quote Wicker1M ( ) How young can a terra-type planet be to have marine unicellular life begin in it's oceans? In Space Engine, I find terras with life that are less than 1 or 2 billion years old.
Hard to say, but the timeline of life on Earth should provide a guide. Apparently, unicellular life can begin quite early if the conditions are right, but multicellular life possibly takes a very long time. Perhaps Earth was late with complex life, or perhaps not and this explains the Fermi paradox.
NIL DIFFICILE VOLENTI
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| Watsisname | Date: Thursday, 29.09.2016, 06:08 | Message # 777 |
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Galaxy Architect
Group: Global Moderators
United States
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| Or perhaps even early... an odd fluke of environmental and evolutionary circumstances. But I think simple life probably develops fairly quickly in general, if circumstances are favorable. It seems that there are a lot of opportunities for it to happen, so that if it can, it does. And we still can't discount the idea of multiple independent geneses of life on Earth -- the shadow biospheres.
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| steeljaw354 | Date: Thursday, 29.09.2016, 09:42 | Message # 778 |
 World Builder
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Pirate
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| Could surface life develop on Ice worlds with an atmosphere pressure with about 1 atmosphere? What sort of surface life?
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| PlutonianEmpire | Date: Sunday, 02.10.2016, 06:07 | Message # 779 |
 Pioneer
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United States
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| I was reading this earlier: http://climate.nasa.gov/climate_resources/24/
With the way things are going, and taking a realistic pessimist route for the future, is it possible we'll cause the CO2 to reach lethal levels at some point, sans natural events like volcanoes?
Edit: And on a slightly unrelated question, how are we affecting he percentages of the other gases in our atmosphere with our constant output of various gases, no matter how much or how little?
Specs: Dell Inspiron 5547 (Laptop); 8 gigabytes of RAM; Processor: Intel® Core™ i5-4210U CPU @ 1.70GHz (4 CPUs), ~2.4GHz; Operating System: Windows 7 Home Premium 64-bit; Graphics: Intel® HD Graphics 4400 (That's all there is :( )
Edited by PlutonianEmpire - Sunday, 02.10.2016, 06:12 |
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| Watsisname | Date: Sunday, 02.10.2016, 09:21 | Message # 780 |
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Galaxy Architect
Group: Global Moderators
United States
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| Quote PlutonianEmpire ( ) With the way things are going, and taking a realistic pessimist route for the future, is it possible we'll cause the CO2 to reach lethal levels at some point, sans natural events like volcanoes?
Do you mean by being toxic to breathe? If so, no. It doesn't become dangerous for breathing until a few tens of thousands of ppm (a few percent). There's not enough carbon stored in fossil fuels to do this. It's hard to compute exactly how high we could raise the CO2 by burning all of known fossil fuels, since it would change the carbon cycling in complex ways, but we could probably push it over a thousand ppm if we wanted to. Of course that would have a very big impact on the climate.
Quote PlutonianEmpire ( ) And on a slightly unrelated question, how are we affecting he percentages of the other gases in our atmosphere with our constant output of various gases, no matter how much or how little?
Methane is the next big one. Combustion of fossil fuels, by oxidizing the carbon, also decreases the concentration of O2 by a stoichiometric amount, but this is a tiny fraction of the total amount of O2 in the air so we don't really notice it. Then there are a large variety of other gases we emit to the atmosphere in smaller amounts, some of which are greenhouse gases or affect the ozone layer or do other things. These can have a variety of residence times, too -- we emit a lot of SO2 for example, but it doesn't stick around for a long time.
Another interesting thing is the increase in the amount of water vapor in the air. This isn't due to an emission of it, but rather because the air is getting warmer and warmer air can hold more moisture. This follows from the Clausius Clapeyron relation, where the saturation level increases by about 7% per degree Celsius.
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