I have came across many theories which highlight's that life came from other planets (particularly mars) , or it originated from undersea or underground.
Talking about life or living thing came from other celestial bodies via asteroids,i don't think thats possible because asteroids hit the earth surface with such a bang and speed , which kills anything on and around it .SO i dont think that is possible, or is it?
| gaurav.baral1 wrote: |
I have came across many theories which highlight's that life came from other planets (particularly mars) , or it originated from undersea or underground.
Talking about life or living thing came from other celestial bodies via asteroids,i don't think thats possible because asteroids hit the earth surface with such a bang and speed , which kills anything on and around it .SO i dont think that is possible, or is it? |
There are 3 main hypotheses. (The overall field of study is called abiogenesis) and a quick summary of the main contenders would be :
Spontaneous Generation. This was first proposed by Aristotle in ancient times and had supporters even up until the 17th Century. The hypothesis states that life spontaneously comes into existence out of decaying organic material. It is easy to see how the idea could arise...maggots 'appearing' on rotted animal matter, for example. It was not until 1862 that this hypothesis was finally put to bed with Pasteur's experiments. Wikki describes the experiment thus: | Quote: |
He exposed boiled broths to air in vessels that contained a filter to prevent all particles from passing through to the growth medium, and even in vessels with no filter at all, with air being admitted via a long tortuous tube that would not allow dust particles to pass. Nothing grew in the broths; therefore, the living organisms that grew in such broths came from outside, as spores on dust, rather than spontaneously generated within the broth. Thus, Pasteur dealt the death blow to the theory of spontaneous generation and supported germ theory.
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Nowadays this hypothesis is not taken seriously by scientists.
Primordial Broth/soup This hypothesis states that life originated on Earth and was formed from a 'soup' of organic chemicals that would have existed naturally in early Earth history. J. B. S. Haldane suggested that the earth's early oceans would have formed a "hot dilute soup" in which organic compounds, the building blocks of life, could have formed. In 1953 Stanley L. Miller and Harold C. Urey (both chemists) carried out an experiment to try and recreate these conditions and produce life from a chemical mixture. Whilst the experiment did not create any molecules capable of self-replication (considered a vital first step in the creation of living cells), it did succeed in creating amino acids which are necessary building blocks for life. They started with a mix of methane, ammonia, water vapour and hydrogen, and then passed a spark continually through the mixture to represent lightning and waited. Another important experiment was carried out by Joan Orσ in 1961, which showed the production of adenine (a key component of nucleic acids) from hydrogen cyanide.
Panspermia This is the theory that life originated somewhere off-earth and exists throughout space in the form of 'seeds'. There are several versions of the theory. The 'strongest' holds that life has always existed and was not created at all. This contravenes several requirements of Big Bang theory and would require a substantial modification to that theory. A 'weaker' version is called exogenesis and it does not state that life is widespread but simply that it was transferred to Earth in the past.
Circumstantial support
There is no experimental or observational evidence which directly supports or contradicts the hypothesis(es) but there are several facts which could be seen as circumstantial evidence. These include:
Narrow window of opportunity - Life evolved on earth very quickly after it's formation (somewhere between 3.5 and 4 billion years ago as compared to the age of the Earth at around 4.55 billion)
Extremophiles - certain organisms have been discovered that can survive in extreme conditions and some bacteria which use chemosynthesis rather than photosynthesis have also been found. Recent experiments suggest that, providing it was sheltered from radiation, life could survive in space for long periods. Such shelter could be found, for example, on meteoroids.
Availability of habitats - observations of our own solar system seem to suggest that possible habitats for life are reasonably abundant. The moon Europa, for example, may well have an ocean of liquid water which could possibly support life. An abundance of such habitats could suggest that life is likely to evolve off-world.
Contra-evidence
Several facts are seen as reasons why this hypothesis is unlikely to be true. These include:
Hostility of space. Space is full of radiations which are harmful to life.
Availability of elements. Nitrogen, Oxygen, Carbon are thought to be vital for life and evidence shows that these elements are not abundant in conditions of sufficient density and/or temperatures outside the environment of Earth.
Impact would destroy life. This fits with your own hunch that the energies produced in an impact by a comet or meteor would be too great for any living organism to survive. There is some evidence, however, to contradict this objection. Firstly it has been shown that much of the energy is carried away by the shell of the meteor by ablation and several meteors have been found where the inside is still cool. Secondly, a sample of hundreds of nematode worms on the space shuttle Columbia survived its crash landing from 63 km inside a 4 kg locker, and samples of already dead moss were not damaged.
Occam's razor. This is a tool used by scientists and basically states that when two solutions are equally possible, the one with the fewest steps (or simplest - and Indi will object to this so I'll add that simplest should be read as meaning 'fewest assumptions' - OK Indi?) should be preferred. Geogenesis (life originating on Earth) requires only one assumption - that life somehow originated on Earth - whereas exogenesis requires at least 2 - that life originated and that it was somehow carried to Earth.
Clay Hypothesis This last hypothesis suggests that life started as crystals, called naked genes, in some particular clays (clays can contain many different atoms and molecules in their structure) and that these crystals gradually grew more complex by interaction with other molecules until DNA related molecules were formed and took control of the organism. This idea was formulated by Dr. Alexander Graham Cairns-Smith in the 1960s but has not been widely accepted by scientists.
Finally - a word about thermodynamics.
Creationists and others who wish to show that life must have been created rather than just 'coming about by chance' will often use the argument that abiogenesis contradicts the second law of thermodynamics.
Simply put, this law states that 'within a closed system, entropy (disorder) will always increase'. These people will say that life represents an increase in order or a decrease in entropy and that this is forbidden by the 2nd law of thermodynamics. Some may genuinely believe this, although the flaw in the argument has been pointed out so many times that, it seems to me, the chances of anyone who has genuinely examined the issue being unaware of the central flaw must be remote.
What this argument fails to acknowledge (or choose to ignore) is the first part of the law - within a closed system. Earth does not form a closed system since there is a net energy flow from the Sun to the Earth. They also fail to acknowledge that the theory allows for a decrease in entropy (increase in order) where work is being done. Life generally consumes energy and uses it to do work of some sort(s) and so does not contravene the 2nd law on this basis either. 
Just to repond to your thoughtd that impact would destroy any life on the commet, an experiment was preformed in which amino acids were, essentailly shot out of a large gun barrel and the resulting impact, instead of killing them, caused the fromation of peptide bonds.
| taragudrig wrote: |
| Just to repond to your thoughtd that impact would destroy any life on the commet, an experiment was preformed in which amino acids were, essentailly shot out of a large gun barrel and the resulting impact, instead of killing them, caused the fromation of peptide bonds. |
Thanks for that. Have you got a reference for the paper/writeup? I'm trying to encourage people to use references if possible to allow verification of claims...it is the 'correct etiquette particulatly in science/....
Chris. | Bikerman wrote: |
...
Thanks for that. Have you got a reference for the paper/writeup? I'm trying to encourage people to use references if possible to allow verification of claims...it is the 'correct etiquette particulatly in science/....
Chris. |
Easy to find, but Bikerman is right, including a source is quite the right thing to do if you can.
http://www.sciencenews.org/articles/20010519/bob13.asp is the first one I found, but Science News is a pretty good mag and there are sources at the end of the article.
| Quote: |
Using a similar megagun at Los Alamos National Laboratory in New Mexico, Blank's team first froze the steel container to better simulate the conditions of a comet. Compared with the Chicago experiments, an even larger proportion of the amino acids in the disks survived. The researchers also found that different peptides formed when they varied the pressure and duration of the impacts by changing the speed of the projectile and the thickness of its tip. |
Interesting science project shooting from the barrel of a gun. Was the gun void of oxygen? Was the atmospheric pressure equal to what an organism would experience in our upper atmosphere? How much radiation was introduced to simulate the radiation upon entry to our atmosphere? This sounds like a great simulation of what it feels like to be an asteroid.
as an aside, not all meteorites hit the earth with a 'bang' there is at least one case of a meteorite that had a much gentler entry, because it has a flat shape the 'hoba' meteorite skipped across the outer atmosphere like a pebble over water, only coming in to land when it was moving much slower ... http://en.wikipedia.org/wiki/Hoba_meteorite so if there was life on it or in it it would likely have easily survived. Maybe life was created by God??. But seriously I think that life started from a random chemical reaction. Some elements just decided to react forming a single cell. From there we slowly evolved.
Yes life formed by complex chemical reactions.
I would say life evolved in the oceans of primitive Earth. The possibility of extra terrestrial seeding of life seems to be a little beyond the limits of probability. But, considering that the evolution of life itself is too much low in probability, we can't discard the possibility that alien life seeded on Earth
On another point of view ...
| llobo1 wrote: |
| Maybe life was created by God??. But seriously I think that life started from a random chemical reaction. Some elements just decided to react forming a single cell. From there we slowly evolved. |
Yes life formed by complex chemical reactions.
But those very reactions are too complex to have happened by themselves. So god must have used what we call " complex chemical reactions " to create life, the universe and everything !!
It's just a matter of perspective, when you realize that whatever we see in this world, we describe it and make rules based on that. All the laws of physics and everything are what they are just because, we first observed them to be that way, and made the laws so that what we observed fits in !!!
That means, if we observe that God exists, we can just make a new law of nature accepting the existence of god and then there will be no doubt about that.
So, God created life using what we call science Yeah I agree with you there. I may have slightly got the tone of my previous comment wrong making it appear that i did not believe in God but this is what happens when you attempt to quickly add a comment before going offline!
The chemical reaction isent realy so complex we secientist have cooy the reaction in lab. So if god was involved he maybe stand for the energy burst that started all.
| Quote: |
Please use quote tags when posting other peoples work. Tags added by Moderating Team
Origin of Life:
Although it cannot be pinpointed exactly, evidence suggests that life on Earth has existed for about 3.7 billion years .
There is no truly "standard" model for the origin of life, but most currently accepted scientific models build in one way or another on the following discoveries, which are listed roughly in order of postulated emergence:
1. Plausible pre-biotic conditions result in the creation of the basic small molecules of life. This was demonstrated in the Miller-Urey experiment.
2. Phospholipids spontaneously form lipid bilayers, the basic structure of a cell membrane.
3. Procedures for producing random RNA molecules can produce ribozymes, which are able to produce more of themselves under very specific conditions.
There are many different hypotheses regarding the path that might have been taken from simple organic molecules to protocells and metabolism. Many models fall into the "genes-first" category or the "metabolism-first" category, but a recent trend is the emergence of hybrid models that do not fit into either of these categories.[citation needed] Despite the length of scientist's current speculations, the origin of life remains as one of science's greatest mysteries. |
| FunDa wrote: |
On another point of view ...
| llobo1 wrote: | | Maybe life was created by God??. But seriously I think that life started from a random chemical reaction. Some elements just decided to react forming a single cell. From there we slowly evolved. |
Yes life formed by complex chemical reactions.
But those very reactions are too complex to have happened by themselves. So god must have used what we call " complex chemical reactions " to create life, the universe and everything !!
It's just a matter of perspective, when you realize that whatever we see in this world, we describe it and make rules based on that. All the laws of physics and everything are what they are just because, we first observed them to be that way, and made the laws so that what we observed fits in !!!
That means, if we observe that God exists, we can just make a new law of nature accepting the existence of god and then there will be no doubt about that.
So, God created life using what we call science |
You don't see the problem in your posting? I'm paraphrasing, but you say if you believe God exists, you just make up a new law of nature, and that proves God exists, because there's a law that says so.The main problem I see with exogenesis is that it still dosn't answer the real question - how did life start? Even if it came from elsewhere in the universe, it still had to have started somewhere. The right chemicals would have had to have come together under the right circumstances somewhere.
All we are doing is widening the field - if it came from 'out there' we can say that it may have formed under conditions we haven't yet encountered.
| Jinx wrote: |
The main problem I see with exogenesis is that it still dosn't answer the real question - how did life start? Even if it came from elsewhere in the universe, it still had to have started somewhere. The right chemicals would have had to have come together under the right circumstances somewhere.
All we are doing is widening the field - if it came from 'out there' we can say that it may have formed under conditions we haven't yet encountered. |
Valid point I think. We also have to consider the point that life apparently appeared on Earth very soon after formation - within about 500 million years I believe, according to current theory. The point with exogenesis that makes it attractive is that it would not necessarily impose the same time constraint on the formation of life that geo-genesis does.
The overall question is certainly still open, as you say.Most scientists have long assumed that life on Earth is a homegrown phenomenon. According to the conventional hypothesis, the earliest living cells emerged as a result of chemical evolution on our planet billions of years ago in a process called abiogenesis. The alternative possibility--that living cells or their precursors arrived from space--strikes many people as science fiction. Developments over the past decade, however, have given new credibility to the idea that Earth's biosphere could have arisen from an extraterrestrial seed.
Planetary scientists have learned that early in its history our solar system could have included many worlds with liquid water, the essential ingredient for life as we know it. Recent data from NASA's Mars Exploration Rovers corroborate previous suspicions that water has at least intermittently flowed on the Red Planet in the past. It is not unreasonable to hypothesize that life existed on Mars long ago and perhaps continues there. Life may have also evolved on Europa, Jupiter's fourth-largest moon, which appears to possess liquid water under its icy surface. Saturn's biggest satellite, Titan, is rich in organic compounds; given the moon's frigid temperatures, it would be highly surprising to find living forms there, but they cannot be ruled out. Life may have even gained a toehold on torrid Venus. The Venusian surface is probably too hot and under too much atmospheric pressure to be habitable, but the planet could conceivably support microbial life high in its atmosphere. And, most likely, the surface conditions on Venus were not always so harsh. Venus may have once been similar to early Earth.
