Donate SIGN UP

How Can Chemistry Become Biology?

Avatar Image
I_Hate_Infinity | 01:39 Thu 21st Feb 2013 | Science
45 Answers
How did life start?
Here's what I know roughly;
~ Big Bang: energy condensed to form nuclei, which formed atoms of Hydrogen;
~ Stellar furnaces: clouds of Hydrogen collapsed under gravity to form the first stars;
~ Super Nova: stars fuse Hydrogen into Helium and dying stars create heavier elements and propel them through space in a massive explosion;
~ Solar System: the Sun ignites and the planets form from 2nd/3rd generation stellar matter;
~ Asteroids: bring water and basic amino acids to early Earth (fundamental molecules for life)
~ Enviroment: volcanic erruptions, ferocious tides, intense lightning and acidic waters...

So I get the story before genesis, atoms and molecules forming from the cosmic soup post Big Bang... And I get after genesis, Darwins evolution of organisms to survive, thrive and multiply... What about genesis itself?

What happened to change chain's of molecules into a living creature that conforms to biology's standard requirements for live: movement, respiration, sensitivity, growth, reproduction, excretion and nutrition.

I presume an Amoeba follows instinct to guide it through life but how did atoms, chained into molecules, "learn" to form DNA for example, or become aware of it's surroundings?

What is science's best guess? Can you refer me to literature/media that could help me understand?

IHI
Gravatar

Answers

21 to 40 of 45rss feed

First Previous 1 2 3 Next Last

Avatar Image
OK 'abiogenesis' is the biggie in Chemistry and Biology - not my exact field but here's some pointers. A lot of interest was first sparked (excuse the pun) by the Miller-Urey experiment back in the 50s which took a lot of the chemicals about in the early earth, heated them and passed a spark through for several days and found traces of most of the amino acids...
09:56 Thu 21st Feb 2013
Question Author
OK, I guess this is my best attempt...

If biologists know the steps chemicals took to form organic molecules, and further that self awareness can occur through favourable evolutionary processes, then there is no mystery.

If we then assume that life will be common throughout our galaxy and others, we can conclude there is nothing special about our emergence in this Universe.

But if we then look at the Universe (i.e. an individual space) and its fundamental laws which have allowed all that's been said, isn't it curious that however it came into existence, it by chance alone it is a fertile Universe?

And to take a step further and we are to assume no devine intervention is necessary, then for the laws of chance not to be violated, mustn't there be great numbers of other 'failed/sterile' Universes (however they are created) to balance the problem of a unique, finely tuned (or even marginally tuned as you put it) Universe? The variables are enormous when you think of how many values one can set for a Universe, so why is it that we find ourself with one so favourable for life?

I conclude the multi-verse theory is seemingly the most logical answer to this predicament. But the damn thing suggests there are an infinite number of other Universes to allow it to be true (I hate infinity grrr.) One can't dismiss the fine tune idea because Humans are hooked up on the idea that we are the only life worth having and they ignore other cosmological variables that could also create life albeit non-human. The very fact we HAVE a Universe with us in makes it 'tailor made' for our existence makes it highly unlikely to just come about by chance...

IHI

(Sorry to move away from thread title but I'm kind of evolving through your feedback)
"If biologists know the steps chemicals took to form organic molecules, and further that self awareness can occur..................."

"If we then assume that life will be common throughout our galaxy and others, we can conclude there is nothing special about our emergence in this Universe."

I would agree.

"But if we then look at the Universe (i.e. an individual space) and its fundamental laws which have allowed all that's been said, isn't it curious that however it came into existence, it by chance alone it is a fertile Universe?"

Not sure about this bit, however. If we find, at some point in our future, that life, complex life, even life similar to our own is relatively common, then you might be able to argue that the laws of physics than govern how our universe works is favourable for the development of life - but I still do not see why people regard that as being so remarkable, so worthy of amazement and awe. Only if you put the cart before the horse and mangle the principles of causality a little does it become noteworthy; only if you imagine a universe created for the purpose of nurturing life, with a selection of universal constants that you can fiddle with to create an ideal set of conditions can you start to think that we live in a "fine-tuned universe".

To me, the development of the universe - from a protean hot uniform plasma, to a vacuum populated with lumps of matter, some of which have developed life is evolution writ large. on a canvas of universal dimensions...Now that is a concept worthy of awe :)

You argue that if we are to disregard divine intervention, then the only other concept allowed is that of a multiverse, if we are not to violate the laws of chance. I think you need to develop that argument a little for it to be persuasive. Why, for instance, does the concept of a single universe, in which an exceptionally improbable event occurs (life), violate the laws of chance? Whilst we are at it, where are the "laws of chance" defined? :)

You stated this "The variables are enormous when you think of how many values one can set for a Universe, so why is it that we find ourself with one so favourable for life?".

I think this is a central point that we keep returning to. Those who argue for the Strong Anthropic Principle, the notion of a "Fine-Tuned Universe" keep returning to this point. Again, I would argue that the thinking is imprecise and woolly - Again it suggests outside interference - the setting of parameter from a huge range. Again it suggests that their is a purpose to the universe, and that life is the ultimate expression of that purpose. But both of those propositions are highly speculative, it seems to me, and ignore logic in favour of wishful thinking :)

And, once again we come back to this fundamental point - For the Fine-Tuned Universe principle to even begin to have any plausibility, you have to offer evidence to suggest that the universe is, in fact, favourable for the development of life - and where is the evidence for that? I would remind you that, based upon the evidence to date, out of the thousands of billions of planets out there, we know of only 1 planet that actually has developed life - Earth. i dont know about you, but 1 in 1000 billion sounds exceptionally improbable to me. Sounds almost more like life has happened here, in spite of the universal constants.......
Question Author
I'm neither for nor against a Creator but I am a gambler and the odds of singularity inflating into a fertile space that life can take hold so easily, when so many other possible universes are potentially sustainable but sterile, are astronomically large. I'm not arguing that it's been arranged like that, quite the opposite. What are the chances of a point of all four forces as one, fracturing and then inflating to allow Chemistry to become Biology?

..."I would remind you that, based upon the evidence to date, out of the thousands of billions of planets out there, we know of only 1 planet that actually has developed life - Earth. i dont know about you, but 1 in 1000 billion sounds exceptionally improbable to me."

This seems like the opposite view of modern astrophysics, to me. From what we know about the creation of our solar system, isn't the belief held that the four rocky planets were created at the same time and in the same way? So they all must have had, like Earth, water and organic molecules delivered to their volcanic surfaces by asteroids and comets during the heavy bombardment. And the belief is that on early Mars and Venus, when conditions were more temperate, life may have started there too. And the reason it is not evident to us now is that the don't occupy the habitable zone of our star and became hostile to advanced forms of life, like we find on Earth.

Because of this study, there is no mystery left or special status of our planet and solar systems, and planets around other stars have been long predicted before evidence of planets were found, thus we must predict similar solar systems to ours, created in the same way ergo having a planet in the habitable zone where life can start.

Your argument against a favourable universe with cosmological constants set precisely (by chance or design) for Humans to evolve, based on your conclusions, cannot be right. All I propose is that it would make more sense for this highly unlikely set of parameters to exist if there were other 'rolls of the dice.'

If you still argue it is not remarkable, do you believe that (a) it's a chance occurrence and highly improbable doesn't mean impossible, we could've fluked it, or (b) [possibly] that when a singularity does fracture, the constants would always have formed this Universe, due to some not yet understood principles governing their division from unison?

Thou I am not trying to force an answer from you from either of those viewpoints :)

IHI
We do seem to be at opposite ends of the spectrum of thinking on this, IHI :)

We can believe and speculate all we want, physicists included, but belief is not evidence. I happen to think myself that we are not the only planet where life of some description has involved, but we do not have any evidence to support that as yet. So, the evidence to date would suggest that intelligent life -life like us - is an extremely improbable event, which does not, to me, suggest a universe finely tuned to develop intelligent life.

I am a gambler too, although I prefer poker to more random chance gambling.

"I'm neither for nor against a Creator but I am a gambler and the odds of singularity inflating into a fertile space that life can take hold so easily, when so many other possible universes are potentially sustainable but sterile, are astronomically large."

If you think we live in a non-anthropic universe, as I do, there is no need to invoke either a creator supernatural entity or a multiverse.

"What are the chances of a point of all four forces as one, fracturing and then inflating to allow Chemistry to become Biology" - I do not understand this comment - could you expand a bit?

"Your argument against a favourable universe with cosmological constants set precisely (by chance or design) for Humans to evolve, based on your conclusions, cannot be right. "

This is, with respect, an example of puddle thinking, as Douglas Adams described it. The puddle looks at the hole into which it perfectly fits, and rather than reasoning that therefore it has developed to perfectly fit the puddle, the puddle has shaped itself to the puddle. By the logic of the anthropic principle, you could argue that hot dogs were shaped the way they were to fit hot dog buns, or that ships were created to house barnacles. We adapt and evolve to fit the physics, not the other way around.

The conditions of the universe have self-evidently shown themselves to be favourable enough for the building blocks for life to exist, as we are here to observe the universe. Thats a long way though from accepting the need for a creator or a multiverse.

Paul Davies, cosmologist, expressed his reservations about the many and varied hypotheses of multiverses;
"Indeed, invoking an infinity of unseen universes to explain the unusual features of the one we do see is just as ad hoc as invoking an unseen Creator. The multiverse theory may be dressed up in scientific language, but in essence it requires the same leap of faith."

He also pointed out that you could describe multiverses as unscientific, since there is no way of testing their existence.

He elaborated further on that concept;
"To be sure, all cosmologists accept that there are some regions of the universe that lie beyond the reach of our telescopes, but somewhere on the slippery slope between that and the idea that there are an infinite number of universes, credibility reaches a limit. As one slips down that slope, more and more must be accepted on faith, and less and less is open to scientific verification. Extreme multiverse explanations are therefore reminiscent of theological discussions."

There are many entertaining and speculative hypotheses surrounding multiverses, linked to speculation about a grand Theory of Everything, of a Fine-Tuned Universe etc ,and it can be fun to do that for sure, but we should not let ourselves get carried away with such speculation :)

You might be interested in his book - A brief history of multiverses ; Paul Davies.

Another variant of the multiverse could be an infinite universe, with many hubble volumes, ie the limit of our cosmological horizons. I quite like this particular theory :)






Sheesh, I really wish there was an edit facility :)

This comment
"The puddle looks at the hole into which it perfectly fits, and rather than reasoning that therefore it has developed to perfectly fit the puddle, the puddle has shaped itself to the puddle. "

Should actually read " The puddle looks at the hole into which it perfectly fits, and rather than reasoning that therefore it has developed to perfectly match the hole in which it resides, it instead elects to believe that the hole has been perfectly shaped to match the puddles shape...

Sorry for the confusion:)
No competent scientist denies that if the laws of nature were just a little bit different in our universe, carbon-based life would never have been possible. Surely such a remarkable fact calls for an explanation. If one declines the insight of the universe as a creation endowed with potency, the rather desperate expedient of invoking an immense array of unobservable worlds seems the only other recourse.

Probably, or the only universe could have just "got lucky" which is why we're here to debate it.
Question Author
I think we are at opposite ends but that's why I like it :)

It seems to that we maybe like battle between fire and ice, the unstoppable force and the immovable object. I'm jumping ahead of experimental evidence and fumbling around in the world of theoretical physics, whilst you are the logic that I need which reminds me, science is the provable facts of nature...

Hmm...

"...not the only planet where life of some description has involved, but we do not have any evidence to support that as yet. So, the evidence to date would suggest that intelligent life -life like us - is an extremely improbable event..."
- Do you mean simple single-celled organisms as common life or more complicated structures as on Earth?
If you accept more complicated life forms as commonplace then I would suggest that; because anthropologist/biologists says human intellect emerged as a result of a large brain, grown and fuelled by a high nutritional diet, I would argue, this is fundamentally a result of being omnivores and top predators. We had a stroke of luck 65 milllion years ago, however it is logical to assume natural events since then (ice ages, volcanic eruptions) would've allowed mammals to fill a vacuum after an extinction level event, so would evolve creatures with intelligence. One must take the systems of life on Earth as the most efficient form because nature behaves that way (e.g. Thousands of species all evolved camera eyes at once because it's naturally the best form).

As you've said there are 100 billion Sun's in our galaxy all with solar systems in various states. If you think life is common the Galaxy, out of all those 'rolls of the dice', you can still conclude life was improbable? Not even mentioning the other 200 billion other galaxies in the observable universe. Intelligence is more likely than you winning with seven, two offsuit!! And we know how often that happens!!

I think the only logical direction take is the acceptance our Universe is receptive to life evolving intelligence, regardless of extinction level events helping/hindering progress. Everything we've found out about our place in the universe has told us we are not special, ordinary star, ordinary solar system, edge of an ordinary galaxy of many. It is right to engage the problem fine tuning presents, even if to get there we must assume that we are not alone in this universe.

I wont be alive long enough to see experimental evidence to back up my claims so I must leave the front line of experimental physics and speculate what goes on behind enemy lines :) - Oh, and I don't like your infinite universe suggestion, as my name suggests! ;)

I think that just like how the mystery of human existence was explained by a creation story and is now understood as just the right condition and enough time, our cosmological constants dilema could just be the evolution of space over time, adjusting itself each 'cycle' to find the most efficient form.
*(A cycle could be a generation, baby universe born [possibly by black holes), or the 'big bounce' theory... Some way to adapt itself and readjust its constants, presumably inside a singularity.) - But still there are the same questions as before, if you don't revert to infinity...

Really sorry for using up the whole 4000 words :S

IHI
We can safely leave Khandros appeal from personal incredulity with respect to an intelligent designer to one side. Unscientific and not supported by any sort of evidence.

I would maintain that the formation of complex life, one capable of abstract reasoning and conscious thought is, based upon the evidence we have to date, an improbable event. Although the base conditions for life - main sequence stars, heavy elements seeded throughout the area from supernova, rocky planets orbiting a star at just the right distance to allow for eventual organic life, the rocky planet being just big enough to retain an atmosphere, cosmic bombardment by meteors and asteroids, delivering additional water, minerals etc, the gradual cooling and development of an atmosphere - all of these features may well be relatively common ( although yet again I stress we have little evidence as yet to support that) throughout the universe.

You still have to develop a chain of development that results in life, and some of the steps along the way mignt be difficult to replicate... certainly if you are going to stick to a carbon- based intelligent life form.

Leaving aside the process of abiogenesis for the moment, we have the formation of ourselves from amino acids and the like. So, first a cell had to be developed. Then prokaryocytes. So at this point we can have vast colonies of unicellular bacteria, like cyanobacteria or archea. Extremephiles, those organisms that live in regions that are highly acidic, or with a very high temperature, are usually prokaryocytes.
Next step in the development of complex, thinking, tool wielding life like us would be eukaryocytes - cells with a nucleus, and a mitochondria, all of which allows for a different form of reproduction. We can imagine colonies forming, and co-operation to survive and flourish. These steps all require eons of geological time.
Fast forward the clock and you get to creatures like dinosaurs. complex, carbon- based, but lacking the abstract though and tool-making skills that humans display. And there we are, for 100s of millions of years, (modern humanity has only been around an eyeblink - 40,000 years or so) , with no record that intelligence like us was developing. And there the story would have remained, had we not had the chicxcalub event and the extinction of the dinosaurs, some 65million years ago. That cleared the way for mammals. But look at all the mammalian species developed - of all of those, only one has the capacity for abstract thought, intelligence and sophisticated tool use - only one.

So i would maintain that getting to intelligent life like ours is an improbable event. Given the sheer scale of the universe however, improbably events will occur and be repeated, so thats why i think there are intelligent life forms out there that we could recognise.

And if you hate infinity, I am surprised you appear keen on the multiverse theory,since that posits an infinity of alternative universes :)
LG; With an imperious sweep you dismiss my request for an explanation above, and instead, assert a series of risible possibilities for the formation of intelligent, conscious, carbon based life form, spontaneously arising by chance against odds which are virtually too great to grasp, while claiming that it is I who is being unscientific. Very distinguished experts give wide ranging opinions on this subject.
Could a Divine spark have set the process in motion?
@ Khandro. Its not risible at all. Your poor grasp of the science is.

The contention that the universe is designed for life is untestable, therefore unscientific. Sorry, but there it is.

You persist in attributing random chance to the development of life - this show how much you fail to understand the process of evolution. Natural selection is non-random and that changes the probability argument enormously.

Divine intervention/ creation/ development is untestable so unscientific. It is also far more unlikely, far more lacking in observable evidence than the non-random process of evolution.

You really really cannot see past this puddle thinking of yours, can you?

@Sandy - Could a deity have provided a spark of life - its a possibility. Is that the extent then of gods hand do you think?
LG; You insist in referring to 'Intelligent design', a theory to which I have never subscribed or even mentioned. The basic problem with ID is that God (for want of a better word) is never spoken of as a “designer” in the Bible or anywhere else, he is called a 'Creator'. It seems that Evolution is one of the principles, like Gravity, which has been used to create the Universe: there is no more a conflict between Evolution and Creation than between Gravity and Creation.
Question Author
I rad recently about information theory, a mathematical analysis of frequencies (whether it be sound, visible light or other spectrums) that when shown in a graph, forms a pattern in a straight horizontal line if the pattern is random and shows a line at 45 degrees when information is being passed through it.

I believe it was inspired by and for the purposes of SETI to detect inter stellar communications but the tested it however on Earth with Dolphin 'clicks', and they found that they were communicating information, talking! From all the other evidence we see that Dolphins are truly intelligent creatures that 'think-out-of-the-box', doesn't this mean we know at least twice on Earth intelligence comprarable to ours has arisen and that the medium Dolphins occupy, water, prevents them from evolving further attributes like hands for tools, study of the stars etc.

Although the theory showed communication between individuals, we haven't deciphered what is being communicated. I believe once we do decode their language, it will show they have higher intellectual thought than say a dog barking to another. Might we be able to teach them about the world in their own language?

If it occurred twice on one planet, might that not be our evidence of natural emergence of intelligence, ergo a Universe with specific cos.constants to allow higher forms of life (be it carbon or silicon)...

LG - And I propose a multiverse to avoid having to resort to ID at this point, but I struggle with the notion of a hyperspce infinite in size with infinite bubble universes. I think I'll go to my grave crying from ignorance long before we figure out pre-big bang conditions...

IHI
A lot depends on how likely or unlikely the universe being the way it is really is. And the simple truth is that we don't know yet. No idea. It could just as easily be that there is "no other way" to have a universe -- in the sense that all of these fundamental constants are somehow fixed by an underlying Theory of Physics that we may never discover -- as that this universe is only one of a theoretically infinite number of possible histories.

And even if it were the case that we got lucky, I've never seen why people find that such an issue. Why does it have to be creator or multiverse/ some other way? Probability works like that, doesn't it? That everything that can happen -- well, can happen. And we're here to observe it all and ask, how did it happen? But if it weren't the way it is we couldn't ask the question anyway.

My own opinion is that we don't really know enough about the Universe yet to really answer the question of how likely or not it was to be this way. And anyway the question is nearly always phrased to imply that somehow it was important for the Universe to sustain Human life and (so far as we know) life nowhere else.
@IHI

I think you are arguing from desire right now :)

"If it occurred twice on one planet, might that not be our evidence of natural emergence of intelligence, ergo a Universe with specific cos.constants to allow higher forms of life (be it carbon or silicon).."

Is the distinction between animals, like primates and cetaceans, qualitative or quantitative? Many have suggested it is a quantitative difference - Darwin himself thought that - but a lot of those researching cognitive evolution now think that it is qualitative difference - a different kind of intelligence.

When people use the term "life" when discussing other planets, it is usually a kind of shorthand for life like ours. And in that sense, life like ours is rare on this planet.

So no, I do not think you have made the case for a universe pre-disposed to generate complex, thinking life. And whilst it is fun to speculate, there is no observational evidence to support either a universe created by some supernatural force, or for an actual multiverse, come to that.

Its fun to speculate,but that is all it is, speculation. I would agree with Jims point, above.




Question Author
Firstly, thank you all for your time to write your replies. Secondly I must stress I have no fixed position in regards to any current theory of such matters, including 'God'/Intelligent Design or the Multiverse. I am purely wading myself through the quagmire of proven physics with my philosophical reasoning, which I understand is dangerous. Although I should respond to a couple of points...

Inyour response to K you said "...You persist in attributing random chance to the development of life - this show how much you fail to understand the process of evolution. Natural selection is non-random and that changes the probability argument enormously."
If evolution is non-random and the process that occurred which ended up in the arrival of man, one can deduce that when the right conditions are met, intelligence should appear (as I argued, has happened twice on Earth.) Couple that interpretation of natural evolution and even taking into account the many worlds life could take hold but not progress to complex organisms, and even the worlds where that stage was not met at all, one can still speculate without concrete evidence that intelligence will emerge outside of our solar system.

If one were to evoke infinity as the state of affairs, the maths tell us that it MUST occur and infinite number of times, in an infinite variety of ways. Although I cannot stand infinity in theoretical postulations, it must be the case if applied to this topic that life is rife throughout this Universe.

And further more, you maintain the argument that intelligent life is improbable as currents evidence shows us, so could you accept two highly improbable occurrences (i.e. the emergence of a fertile Universe with its specific constants and then the likely hood it does create intelligence) as pure coincidence? There are an awful lot of coincidences that happened to aid our evolution, shouldn't it make more sense if there were other realities with other permutations making our specific Universe more likely to occur?

IHI
You certainly can speculate that we'll eventually find life elsewhere, and surely I believe that we will -- but we haven't yet. As long as that remains the case, it's also possible that we will never find life anywhere else. So for now the best thing to do is to make the observation that life, and intelligent life, doesn't seem to come around that often. Perhaps after all it will be seen as a regular occurrence. But at present the only evidence for that is probabilistic estimates.

I think you're again misunderstanding infinity. If there are an infinite number of stars in our universe, or an infinite number of universes, it still does not follow that there is an infinite number of places where life emerged. The nature of infinity is such that what happens when you "get there" so to speak depends on "what route" you took to get there. It may be the case for example that intelligent life emerges almost everywhere it can, in which case yes, we can expect a lot of company. Or perhaps the circumstances are such that so few planets can sustain life, and even the ones that can get hit at the wrong time by a cataclysmic event. One can imagine a function that predicts how many places you will find life in the universe, that tends to a limit as the number of places you look at tends to infinity. That limit may even be one, i.e. here on Earth. Again, while I don't believe that ours is the only planet with intelligent life for a second, the maths does not "prove" that we aren't until we know what the maths is. There is anyway no "must" about it.

Finally in the "coincidence" thing -- yes it appears unlikely but improbable events suddenly occurring don't demand lots of trial universes or a guiding hand behind it. They can happen by chance. Not only that but it assumes that somehow the end result is that most desirable. But we tend to notice only those and ignore the other, equally unlikely, undesirable chains of events. How lucky, for example, for the most recent lottery draws to be what they were, with odds against that specific set being apparently (if my maths is correct) in the order of 10^57 to 1 ! Yet that set happened. Some set had to happen, and it was just that set. Similarly on this planet, something had to happen, and it was just our particular history and set of people, however vanishingly small a probability that history had of occurring.

The mistaken assumption, or at least I think it is mistaken, is that the universe in some sense had to create life. As soon as you get past that, the fact that it did becomes less remarkable, because something had to happen and we were just that something.
I keep meaning to read this thread in detail but the posts are so long (and deep) I've not found time yet. Apologies.


Random change is involved in the creation of mutations that add variety to the genetic pool. Selection is less random, but even there, there is no accounting for taste. I believe much of the differences we see for the larger animals are down to sexual preference, which I think is why we see different human races. Naturally beneficial changes survive, but randomness still defines what there is to choose from.

I don't see how one must invoke infinity in any of this. A large enough number works too. But should one do so then an infinite number of places where life might emerge may still end up with no life, or one example, or an infinite number of them. Instinctively we would tend towards the last option as feeling most reasonable but if there is an infinitesimal change of life then the number of occurrences could be anything.

If one doesn't not extend evolution to cover the initial emergence of life then sure, there is no conflict between a creation belief and how evolution made changes from there on. But I suspect most who accept evolution see no reason to except the emergence of life from the same or similar process and replace it by an act of creation.
Have read through, not tried the links. I'm beginning to think this thread is edging towards a philosophical/religious debate rather than a scientific one.

To me, constants being set doesn't necessarily imply a being/deity having the ability to change them, merely that they had to be something and 'set to' is a shorthand way of referring to what they turned out to be when measured. That's not to say we have proved they could never be something else, maybe in a different universe, or even in a far away part of our own. Perhaps the values drift over distance somehow ?

Maybe it's just my interpretation of the above but sometimes I get the feeling that an individual arguing one side of the discussion isn't always getting what the other side is saying ;-) But it's possible I'm mistaken. Keep up the good work ;-) it makes for interesting reading if one has the stamina to plough through.

21 to 40 of 45rss feed

First Previous 1 2 3 Next Last

Do you know the answer?

How Can Chemistry Become Biology?

Answer Question >>