What Properties Make Earth Habitable for Life?

[red_fox77]

There must be a fundamental property of the Earth that allowed/encouraged life to deveop. Identifying these will help identify other planets that also could contain life. Sorry if this is a repeat thread, I didn't see anything exactly like it.

The two more obvious traits are the magnetic field to deflect radiation, and a large moon to generate tides and help stir the atmosphere and oceans. Any others that are required?

 

[pebrew]

of course since we've never found life elsewhere we don't know exactly what aspects of Earth's environment are necessary and what are simply incidental.

one that is frequently mentioned as a key is our abundence of water. water has a lot of amazing properties, most of which ellude me right now. though i recall it is sometimes referred to as the 'universal solvent' since it can dissolve so many various elements. which is clearly important if you need to move lots of different molecules and elements in a medium, such as within a plant or animal.
since water expands as it freezes it helps break down the jagged terrain of igneous rock. making soil, allowing carbon to break out of crystal form, etc, etc.

i believe the general stability of our climate/temperatures is also cited as an important factor. however this aspect seems to arise from the current coincidence of a number of disparite mechanisms that aren't necessarily causily linked. water, ghgs, the magnetic field, relatively little volcanic activity, correct distance from a star, the Earth's short day, and other factors all play a major part in climate stability.

i'd go on waving my hands, but I'm sure others here will have much better described properties and reasons behind them.

 

[matthyaouw]

i believe the general stability of our climate/temperatures is also cited as an important factor.

Isn't much of our climate stability due to the presence of life however? Two major carbon sinks in the world are Photosynthesises, and carbonate secreting organisms, and without these, atmospheric carbon would be at an extremely high level, and oxygen at an extreme low.

It's not so much a question of what are the properties of Earth that promote life, but what were they 2 or 3 billion years ago?

 

[kirkmcloren]

The odds of not having a favorable environment are -- (pardon the pun) astronomical.
Not only must oxygen be in a range high enough to support life -- and that means pressure as well as percentage.
There must be adequate water and it must be liquid.
We also see that chemical reactions are very thermally dependent thus fevers over 107 are lethal.
It seems that the necessary chemical reactions for life preclude non carbon based life if you want an organism as complex as a human.
The distance from the star, the temperature and size of the star and to some extent the spectrum of the star are critical to temperature of the planet and the necessary wavelengths and intensity must be there for photo based life (plants).
I think these points are good for starters.

I think the odds must be 1 in billions or trillions for a suitable environment.

 

[tumor]

There must be a fundamental property of the Earth that allowed/encouraged life to deveop. Identifying these will help identify other planets that also could contain life. Sorry if this is a repeat thread, I didn't see anything exactly like it.

The two more obvious traits are the magnetic field to deflect radiation, and a large moon to generate tides and help stir the atmosphere and oceans. Any others that are required?

Nothing fundamental about life on earth,we know very little about other planets not to mention other solar systems.Cosmos might be swarming with life.
Life could evolve in different ways, not necesserly needing Earth like environment.
We have much more yet to discover.

 

[kirkmcloren]

We may not have craft that can visit other planets but we do know enough chemistry and physics to have intelligent speculation. Also there is a lack of any electromagnetic emissions as evidence of other intelligent life (SETI). Hardly teeming.

For example---

http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/980221b.html

Scientists have occasionally speculated that life could be based on an element other than carbon. Silicon, being the lightest element with an electronic structure analogous to that of carbon (having a half-filled outer shell with 4 unpaired electrons), is the most likely candidate mentioned. However, carbon's tendency to form the long chains and rings that form the basis for organic compounds that at some level of complexity begin to self-replicate is unique. Also, because older stars naturally produce carbon, along with nitrogen and oxygen (its neighbors on the periodic table), it is relatively abundant in the universe. Many astrophysicists who study the spectra of stars believe that complex chains and even rings of carbon appear in such unlikely places as stellar envelopes (e.g., in the form of PAHs, polycyclic aromatic hydrocarbons). When such compounds reach cooler regions of space where they can bond with readily available hydrogen, organic compounds as we know them are naturally formed.
Although other elements may form complex, covalently bonded structures, none has the rich molecular variety of carbon. It is the chemistry of carbon that allows us to consider the possibility of life "as we know it" in other parts of the Galaxy and the Universe beyond. We do not know whether Earth-like conditions exist elsewhere; but if they do, it is highly likely that life forms, if they exist, will be based on carbon.

One more point: The organic types of structures appearing in stellar envelopes are very hot and probably stripped of hydrogen, so that they are not themselves alive; it is only when carried off to a more hospitable environment, such as a much cooler planet 100 million miles away or so, that the kind of chemistry required by life becomes possible on a scale large enough to allow for stable development and replication. Water is also a factor, causing the hydrophobic proteins to clump together at all, and serving as a medium a conduit for new material, protection from temperature changes and harmful stellar radiation, etc.

Mark Kowitt and Damian Audley
for Ask a High-Energy Astronomer.

 

[Phobos]

Not only must oxygen be in a range high enough to support life -- and that means pressure as well as percentage.

Life on Earth started before the high-oxygen atmosphere we have today. The oxygen content in our atmosphere is a result (byproduct) of life.

There must be adequate water and it must be liquid.

It's true that a lot of the current exploration is focused on places with liquid water.

We also see that chemical reactions are very thermally dependent thus fevers over 107 are lethal.

107 is lethal for humans (and presumably closely related animals). Other species we know of find that downright chilly (thermophiles).
http://www.nps.gov/yell/nature/thermophiles/biopro.html

and the necessary wavelengths and intensity must be there for photo based life (plants).

Presumably, if the other conditions are right, then photosynthetic species may be able to adapt to a variety of solar outputs.

I think the odds must be 1 in billions or trillions for a suitable environment.

Life on Earth has managed to survive in a wide variety of conditions...high/low pressure, high/low temperature, aerobic/anaerobic, acidic/alkaline, high in the atmosphere/deep in the earth, lots/little water, lots/no sunlight, etc.

I think there are many chances for suitable environments, particularly for microbial-type life. The trick would be in whether life could get started. That process is not well understood.

 

[Phobos]

We may not have craft that can visit other planets

I assume you mean planets of other stars since we are exploring other planets in this solar system right now.

Also there is a lack of any electromagnetic emissions as evidence of other intelligent life (SETI). Hardly teeming.

If life on Earth is any indication, then a technological civilization capable of emitting radio waves into space is a tiny fraction of the overall scope of Life. For all we know, the universe could be teeming with bacterial life. Technological intelligence would be necessarily rarer and, odds are, widely separated. That means it takes time to transmit signals. SETI has only been at work a few decades and has only examined a narrow portion of the overall EM spectrum across the entire sky.

 

[garytse86]

consider the anthropic principle

 

[Genius of Physics]

the only answer from me is god god have created life on Earth it is not luck or something like that I am not religious but the only thing what is existing is god this world could be something like matrix who knows but onething you can believe on is god god do not doing something with this world we do

there is not coming nothin from nothin i believe that, The gods rules are the Physics laws and they could not be breaken 0+0=0
maybe it will not answer your qustion but it is a theory for you but it is real
SORRY THAT IM SAYING THIS FOR YOU BUT EVOLUTION AND CHARLES DARWIN THEORY IS SOME BUL**** LIKE I SAID 0+0=0
for me i may have some grammatic problems

 

[Phobos]

there is not coming nothin from nothin i believe that, The gods rules are the Physics laws and they could not be breaken 0+0=0
maybe it will not answer your qustion but it is a theory for you but it is real
SORRY THAT IM SAYING THIS FOR YOU BUT EVOLUTION AND CHARLES DARWIN THEORY IS SOME BUL**** LIKE I SAID 0+0=0

The theory of evolution is one of cause and effect, not something-from-nothing. Perhaps you can explain why you think evolution comes from nothing.

 

[dekoi]

This is beginning to enter philosophical reason and not scientific explanation.

Consider the statement, "Everything with a beginning, has a cause, and consequently an end." Therefore if evolution had no beginning, it would not have a cause.

 

[garytse86]

our universe had a beginning, but does it have a cause?

If there is no cause for evolution then why does it exist?

 

[dekoi]

Once again, everything with a beginning has a cause. Thus, evolution must have a cause, since it had a beginning.

 

[Genius of Physics]

i knew that you would say it now my answer: evolutions says that we are coming from apes and our body and mind is becaming slowly better and better but if you think about that then we will be live in the sun after 5 billion years so believe in that or not but it is infront of your eyes and you can see that someone made bigbang, somebody says that it came from the black holes that suck up eash others and at last they explode.
My answer we will die sometime but the universe never ennd it will cycle like the water cycles the Earth and by the way how old are you i am 15.

 

[Genius of Physics]

This is beginning to enter philosophical reason and not scientific explanation.

Consider the statement, >>>>>>>>>"Everything with a beginning, has a cause, and consequently an end."<<<<<<<<<<<<<<<< Therefore if evolution had no beginning, it would not have a cause.

thIS IS mATRIX YOUVE SEEN TOO MUCH TELEVISION
LIFE HAS AN END BUT NOT THE UNIVERSE

 

[dekoi]

thIS IS mATRIX YOUVE SEEN TOO MUCH TELEVISION
LIFE HAS AN END BUT NOT THE UNIVERSE

Firstly, i understand evolution is not linear. Keep that in mind.

Our mind is not becoming "better". And by stating "mind", you are admitting your belief of metaphysics.

The Earth will die, so will the universe; since everything with a beginning has an end.

Life has an end, so does the universe. Since life has a beginning, and so does the universe.

 

[garytse86]

surely the universe will have an end?

 

[Genius of Physics]

"surely the universe will have an end?"
ididnt say that the Earth will not die but i believ that it is going to be a big crunch and then big bang allover again and that will never end daont you think atoms or rays can not dissepear don't you think that if not then explain what "maybe" will happen

 

[garytse86]

but there isn't going to be a crunch though because the rate of expansion is increasing due to some mysterious dark energy...

 

[Phobos]

Therefore if evolution had no beginning, it would not have a cause.

The beginning of biological evolution was with the formation of the first self-replicating molecule.

 

[Phobos]

If there is no cause for evolution then why does it exist?

The cause of evolution is the differential selection of varying alleles (gene types).

 

[Phobos]

but there isn't going to be a crunch though because the rate of expansion is increasing due to some mysterious dark energy...

Correct. The current evidence indicates that the universe will expand forever. Eventually, matter will fall apart and energy will fizzle out to lowest levels. There does not appear to be enough matter in the universe (i.e., enough gravity) to pull it all back together into a Big Crunch. Of course, research goes on...

 

[dekoi]

The beginning of biological evolution was with the formation of the first self-replicating molecule.

And what was the beginning of the self-replicating molecule? Surely, there must be an initial sample of matter which created or was formed into this self-replicating molecule.

 

[matthyaouw]

Last I heard, the beginning of life/evolution was probably when a collection of phospholipid molecules formed something like a cell membrane, allowing conditions within it to change in comparison to the water it was in.

 

[Brad Barron]

I have many theroies about why life is currently on Earth. One theory that makes some sort of logical sense is that at one point, there was life on each planet, but that life on the other planets in our solar system died off leaving our planet with the most recent timeline of biological beings existing.

-Brad Barron

 

[Leaping antalope]

Oxygen and liquid water...they are essential to life on Earth.
However, I got an idea from an interesting movie:
Life on Earth is generally based on the element carbon. What if life on other planets are based on another element such as nitrogen or helium? Their way of life is then totally different from ours. Maybe different life forms have different suitable conditions...

 

[Phobos]

And what was the beginning of the self-replicating molecule? Surely, there must be an initial sample of matter which created or was formed into this self-replicating molecule.

Yes, but that process remains a bit of a mystery. However, it has been demonstrated that abiotic (non-life) processes can form a variety of amino acids from the types of organic molecules that were present on the early Earth. Amino acids are the building blocks of proteins, which are the building blocks of life.

Also note that the dividing line between life & non-life is likely a gray area. I don't know if you would call a self-replicating molecule "alive" just like people hesitate to call a virus or a prion "alive". However, once we have self-replicating cells (like bacteria), then we are more comfortable calling it "life".

 

[Phobos]

I have many theroies about why life is currently on Earth. One theory that makes some sort of logical sense is that at one point, there was life on each planet, but that life on the other planets in our solar system died off leaving our planet with the most recent timeline of biological beings existing.

If life could form so easily, then you might expect it to re-form again on planets where life went extinct.

It will be interesting to see if we ever find signs of life on Mars (or elsewhere) so we can get some idea of how commonplace life is.

 

[Phobos]

Oxygen and liquid water...they are essential to life on Earth.

Well, at least liquid water is. There is a large slice of life that does not require oxygen (e.g., anaerobic bacteria such as those living in your digestive tract). The quantity of oxygen in our atmosphere formed as a waste product of early lifeforms on Earth. Other species then evolved to take advantage of that oxygen.

However, I got an idea from an interesting movie:
Life on Earth is generally based on the element carbon. What if life on other planets are based on another element such as nitrogen or helium? Their way of life is then totally different from ours. Maybe different life forms have different suitable conditions...

Try poking around the archives...I think there were some recent discussions similar to this idea.

p.s. Welcome to Physics Forums, new members!