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Key component of life's building blocks could have come from space

Sun, 6th Mar 2011

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The origins of life on earth are a hotly debated topic among scientists. One theory suggests that, even if whole organisms didn't come to earth carried by meteorites, then maybe meteorites brought some of the chemical building blocks for amino acids the molecules that make up proteins. Now tests on a meteorite with the catchy name CR2 Grave Nunataks 95229 provide more evidence that meteorites might have brought these building blocks to earth, kickstarting the chain of events that led to the evolution of life here.

CR2 Grave Nunataks 95229 is a type of meteorite called a carbonaceous chondrite meteorites that contain a range of organic chemicals including amino acids. Because of this, some scientists think that they might have 'seeded' earth with these chemicals when they fell from space, providing the primitive building blocks for the formation of DNA and proteins, which ultimately led to life as we know it. But studies of similar meteorites haven't come up with solid evidence for this, as the chemicals they contain are a real mix of all kinds of things most of which couldn't easily be used to create molecules of life.

Chondrite meteoriteThe Grave meteorite spun off from an asteroid and landed in Antartctica in 1995. Researchers, led by Sandra Pizzarello and her colleagues in the US, analysed the chemical makeup of the  meteorite using high pressure water at a temperature of 300 degrees centigrade conditions designed to mimic both the asteroid where the meteorite was made, and the conditions on the early earth.

Publishing their results in the journal PNAS this week, the team discovered that their asteroid contained surprisingly high amounts of ammonia a chemical precursor to amino acids. These levels were much higher than might be expected on earth at the time.

Given the chemical makeup of similar meteorites, and the fact that most of these only contain compounds built of rings of carbon atoms, this is an unusual find indeed, and the first of its kind. Further analysis showed that the ammonia in the meteorite could only have come from the original asteroid it came from, and suggests that there was a lot of ammonia around in that environment.

Nitrogen, which is a key part of ammonia, is the fourth most common reactive element in the universe. Here on earth, it's a vital component of proteins, as well as DNA and RNA the genetic information within living cells and it's indispensible for life. Ammonia plays a key role in many chemical reactions, including the reactions that create the molecules of life.

But from what we know of the conditions on the early earth, it's been hard for scientists to figure out how this might have worked back then. For a start, evidence suggests that the early earth's atmosphere wasn't relatively rich in ammonia. And we know that sunlight can also break down the chemical, which would have been a  big problem at the time.

But the discovery that meteorites can actually contain relatively large amounts of ammonia suggests an alternative route for the chemical to turn up and get involved in the chemical reactions that might have led to the generation of the molecular building blocks of life all those millions of years ago. And it adds weight to the idea that at least some of the molecules that kickstarted life on earth may have come from space.



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pretty interesting, thanks for the link Blashyrk, Wed, 9th Mar 2011

This is a great theory, I have delved into the inklings that biological life may have been carried by cellestial vector objects moving through space that entered the earth's atmosphere and brought the micro-orgnisms into the "perfect" breeding grounds for life to evolve. However, the theory that instead, these vector quantity objects brought the chemical compound building blocks necessary for life to form is a much better one. It makes sense that these copounds came form the chemical make-up of these bodies rather than taking a wild ride on the surface through space where they would indeed be inhibited on frozen biological matter, they would also be exposed to all of the dangerous and destructive radiation, of which there would have been much higher volumes in the earlier stages of the universe. But then that still leaves us with the question: why did these chemical compounds form in these asteroids and other cellestial bodies and just what were the probabillities that these exact samples were to collide with this planet out of all of the satellites in the universe, and how do we know that the same thing hasn't happened elsewhere in this enigmantic cosmos and how many more times could this happen. In other words, this is an extraordinary case in which there is a lot of entorpic circumsances to consider. However, one thing is certain, and that is that entropy tends to "centre" or "even" out uniformly the more that it occurrs and that highly unlikely circumsances will happen no matter the odds. so, if this highly improbable event has occurred once, then it will tend, over time, to uniformly occurr. But on that note, there is yet another problem. That is that these occurances must occur over the entire expanse of the universe in order to be uniformly present. So, for all that we know, we could have neightbours in our visible space, or to get you thinking, in farther reachres of the universe which we cannot see but, those intelligent life forms are very familliar with or quite the opposite, in which life is new and still in the basic protein stages or even not yet there. The basic point of this all, is that yes this could in fact be the way that life was brought to this planet, but it still cannot answer why or how many more times on how many different planets this has occurred on, and even more inportant than all of that, is the question; "Why?". kvantovoi kvark, Mon, 28th Mar 2011

One could, of course, claim that the entire Earth was built out of meteorites...  and thus, the planet forming meteorites in the solar system necessarily brought the building blocks of life. 

How much of our crust is formed from late bombardment meteorites?

Isn't that only true in an oxidizing atmosphere.  It would not be true in a reducing atmosphere.  Ammonia should last quite some time in an oxygen poor atmosphere.  Would it react with CO2?  Is that a bad thing?

What would be most interesting would be if a protein would be found in an asteroid, consisting of a chain of at least 3 or more generally recognizable amino acids with peptide bonds between them.  Perhaps a snippet of DNA that could not be attributed to a terrestrial source.  We might need to mine some asteroids to prevent terrestrial contamination.

CliffordK, Tue, 22nd Oct 2013

What is the chemical makeup of water from a geyser or hot spring?

Perhaps now that Yellowstone is reopened, I should take a trip out there. 

The problem with abiogenesis around a deep sea vent is that there may not be enough to keep proto-life from being washed away over years, centuries, or even millennia.  Around a hot spring, on the other hand, one might expect energy + a slow buildup of chemicals which might be more conducive to abiogenesis.  CliffordK, Tue, 22nd Oct 2013

I can see that the question is opening up into two threads: (a) how did life begin (anywhere) and (b) did it begin on earth or somewhere else?

I think the second question is as amusing as angels dancing on a pinhead, but much less interesting than the first. We have no reason to believe that this planet is uniquely hospitable to DNA chemistry, but given that it (or somewhere like it) is hospitable, how did the first cell form? And even more to the point, how did its daughters form? alancalverd, Tue, 22nd Oct 2013

It likely will be impossible to determine if life truly began on Earth, or on a planet around a distant star that went through a calamity (supernova, large impact, etc).  I suppose if we found something indicating organic origins on an asteroid too small to support life or abiogenesis, then one could assume that it was transported here.

Finding a few scattered carbon compounds and carbon/nitrogen compounds doesn't necessarily indicate that they were formed by life, nor that they were a critical component of the formation of life here on Earth.

There seems to be a lot of evidence to support that prokaryotes were the first life on Earth.  However, some of the hardiest organisms on Earth are also the prokaryotes, and it doesn't mean that they didn't come from elsewhere, or perhaps substantial parts of them which then managed to reconstitute here. CliffordK, Wed, 23rd Oct 2013

Researchers wanted to determine if amino acids embedded in comets could survive an impact with the Earth, so they fired a 'snowball' laced with them at very high velocity into a target. They found that the amino acids readily linked up to form peptides with considerably more than three components. If you (or anyone) wishes I shall try to locate the relevant paper. Ophiolite, Wed, 23rd Oct 2013

We are all star dust..

EVERYTHING, has come from somewhere. Why does it matter if amino acids came on an asteroid, it makes no difference to the reason life began.

Amino acids could quite happily have formed on this planet, all the building blocks were there and the chemical reactions would take a little bit of time, but follow a trend, CO2 > HCN > CH3OH > CH7OH and onwards. I would say though some teachings out there are advocating the building blocks of life starting before boundaries (such as cell walls) were formed, this i find highly unlikely as in order to form a boundary, all you really need is a collection of molecules with a hydrophilic and hydrophobic end, and this will allow them to clump up with a 'dry' interior against the wet exterior. (even simple hydrocarbons can do this)

The big question remains though, WHY do the natural chemical reactions WANT to happen, WHY do the chemicals do what they do during cell division.. the 'what reactions occur' is no longer really important, its the driving force behind it we need to discover.. why does every living thing try to produce ATP at all costs? or is it doing something else really important that it NEEDS to do.. chemical reactions within a ball of organic stuff should not NEED to do things, such as create an identical ball of organic stuff for the same things to happen. We can play with the reactions and show that we could (given the right environment and nutrients etc) get it so that there is more stuff that the organic ball of stuff can hold so it has to split (thinking oil fragmentation in water) but then what makes the reactions NEED to climb towards the sun so that it can do so, WHY would it actively put effort into getting more stuff than it can contain so it splits? When does it go from accidental to intentional. SimpleEngineer, Tue, 29th Oct 2013

If you have a liposome, is it already selectively permeable, or what would also be required? Can it trap things? Or does it depend on what's already inside it? cheryl j, Thu, 7th Nov 2013

The more we understand HOW, the further WHY recedes from significance.

If we start from an anthropic point of view, we are looking down the wrong end of the telescope: as sentient humans we set a lot of store by intentional outcome and assume that everything we or other sentient animals do, is done for a purpose. But if you consider purpose to be an emergent quality of a complex system that has a concept of sequence and time, you can see that it isn't an essential input into a simple system like a single chemical reaction.

Now consider a two-stage reaction A + B -> C and C + D -> E, with a counter-reaction A + D -> F. To get to E we need to introduce "purpose", "delayed gratification", or an "F inhibitor". The evolutionary model suggests that the "F inhibitor" is the most likely HOW, and eliminates the need for a WHY.

It's a lot more complicated than "goddidit", but a heck of a lot more plausible if you start with  budget of  14,000,000,000 years, infinite resources, and no specified outcome - i.e. the right end of the telesope.

It's all summarised in the Irish advice to navigators. "So you're wanting to get to Cork? Well, sir, if I was you I wouldn't start from Dublin." alancalverd, Thu, 7th Nov 2013

The how is getting Found, but the start is always a WHY..

A Why leads to a How..

My big why is, why do these reactions want to gather energy and reagents TO occur. Living things have sought out materials to create new ones of them.. if it is all chemical reactions, the current How doesn't answer that question. We all know how babies are made.. But why does every living thing have a natural urge to procreate? If we can find out.. maybe we could do something about world population.

(quick thought, is this what chemical castration does?) SimpleEngineer, Thu, 7th Nov 2013

No, it's a how. If you mix A and B and the product C has lower energy or more entropy, you will eventually end up with C.

Why do living things procreate? Because if they didn't, the species would have died out, so what we are left with is just those species that do procreate.

The way to reduce world population is to make it economically worthwhile not to reproduce. I have an urge to stay in bed but an economic need to go to work, so each day I make an informed conscious choice. If I could buy a "work pill", I'd probably do so. So if it's economically sensible not to have babies, and you can buy a pill that prevents pregnancy, you have a Western society.  alancalverd, Thu, 7th Nov 2013

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