Origin of life

[Altfish]

"Scientists are not close to knowing the exact processes that took place on the earth which led to the origins of life. They may never know the exact answer because the evidence for this very primitive life has probably been destroyed by the more efficient life which evolved from it."

Does anyone know of any theories as to why they don't know, or a way that could explain this in a little bit more detail?

I read that scientists theorize that RNA came before DNA. I couldn't find anything Theorizing what came before RNA. Does anybody know if they have theorized something before RNA?

Isn't that exciting?

Scientists will not be made redundant because there are still things to be discovered.

Scientists do not "Theorize" about anything. "Theory" has a very specific meaning in science; it is not a 'guess'.

 

[Polymath257]

"Scientists are not close to knowing the exact processes that took place on the earth which led to the origins of life. They may never know the exact answer because the evidence for this very primitive life has probably been destroyed by the more efficient life which evolved from it."

Does anyone know of any theories as to why they don't know, or a way that could explain this in a little bit more detail?

I read that scientists theorize that RNA came before DNA. I couldn't find anything Theorizing what came before RNA. Does anybody know if they have theorized something before RNA?

Well, part of the problem is that the original environment was about 4 billion years ago and quite different than conditions now. But finding remains from events 4 billion years ago isn't so easy. What that means is that, even if we discover a way to produce life in the lab, we won't know if it is the same process as happened on Earth at that time. The specific information may well be lost.

But, what we can do is look at life today and search for commonalities. And what we find it that ALL life on Earth is a chemical process. The fundamental molecules of life are all polymers: they are long sequences of rather simple pieces linked together to form larger structures. The basic pieces are amino acids (for proteins), nucleic acids (for RNA and DNA), sugars (energy source, but also doing other jobs, like immune signaling), fats (cell membranes, for example).

So, what do we know?

First, that life is a complex collection of chemical processes. Nothing 'extra' is required in addition to the chemistry to produce life. The question isn't changing 'non-living matter' into 'living matter', but how to organize the basic chemicals so that they interact in a way that *is* life. No molecule in your body is alive. But the way those chemicals interact *is*.

At the heart of all life today is DNA. DNA forms long molecules made from nucleic acids. It encodes the information for how to make proteins. But to actually form the proteins, the information from the DNA is rewritten into RNA, processed by RNA, and it is RNA that links the amino acids together to form proteins. We also know that RNA is able to promote (catalyze) many reactions important for life, including the ability to promote its own formation. This is the basis for the RNA world hypothesis.

On the other end, we know that primitive atmospheres tend to have a lot of methane, cyanide, ammonia, and other simply molecules. We see these in gas clouds in outer space as well, so they are incredibly common. We also know that these compounds will, when subject to electrical discharges (lightning), form the more complicated amino acids and the other building blocks for the polymers of life.

We also know that fats (lipids) will spontaneously form spherical 'bubbles' (vesicles) that can encompass other compounds and provide a concentrated environment for them to interact. These 'microspheres' can look quite similar to simple cells, including the ability to 'bud'.

Finally, we know that life existed by 3.8 billion years ago. It was 'simple' life, single celled bacteria, but it was alive. More complex cells didn't start to form until about 1.5 billion years later. and multicellular life not until another billion or so years after that. Humans have been around about 1-200,000 years--a very short time period on this scale.

What we don't know: what was before the RNA world and how it came about. It may well have formed spontaneously from the nucleic acids already present through sequences of drying and wetting (which promotes the formation of the bonds and makes those polymers).

We don't know how the transition from the RNA to the DNA world happened.

We don't know when and in what roles proteins started being important for life. How much original metabolism was catalyzed by RNA and how much by proteins (like today)?

We don't know under what conditions the first life formed. Speculations include the ability of clay to promote certain reactions in the early stages, the chemistry to deep sea vents, and the cycles of drying and wetting that happen in small ponds.

On the other hand, we know a LOT more about the basic chemistry of life than we did 20 years ago. We know that nucleic acids can be produced in large enough quantity to allow for further reactions leading to RNA.

So, progress is being made, slowly but surely. There are still many questions, but we know more now than we did 20 years ago, and that was more than 20 years before that.

 

[King Phenomenon]

Well, part of the problem is that the original environment was about 4 billion years ago and quite different than conditions now. But finding remains from events 4 billion years ago isn't so easy. What that means is that, even if we discover a way to produce life in the lab, we won't know if it is the same process as happened on Earth at that time. The specific information may well be lost.

But, what we can do is look at life today and search for commonalities. And what we find it that ALL life on Earth is a chemical process. The fundamental molecules of life are all polymers: they are long sequences of rather simple pieces linked together to form larger structures. The basic pieces are amino acids (for proteins), nucleic acids (for RNA and DNA), sugars (energy source, but also doing other jobs, like immune signaling), fats (cell membranes, for example).

So, what do we know?

First, that life is a complex collection of chemical processes. Nothing 'extra' is required in addition to the chemistry to produce life. The question isn't changing 'non-living matter' into 'living matter', but how to organize the basic chemicals so that they interact in a way that *is* life. No molecule in your body is alive. But the way those chemicals interact *is*.

At the heart of all life today is DNA. DNA forms long molecules made from nucleic acids. It encodes the information for how to make proteins. But to actually form the proteins, the information from the DNA is rewritten into RNA, processed by RNA, and it is RNA that links the amino acids together to form proteins. We also know that RNA is able to promote (catalyze) many reactions important for life, including the ability to promote its own formation. This is the basis for the RNA world hypothesis.

On the other end, we know that primitive atmospheres tend to have a lot of methane, cyanide, ammonia, and other simply molecules. We see these in gas clouds in outer space as well, so they are incredibly common. We also know that these compounds will, when subject to electrical discharges (lightning), form the more complicated amino acids and the other building blocks for the polymers of life.

We also know that fats (lipids) will spontaneously form spherical 'bubbles' (vesicles) that can encompass other compounds and provide a concentrated environment for them to interact. These 'microspheres' can look quite similar to simple cells, including the ability to 'bud'.

Finally, we know that life existed by 3.8 billion years ago. It was 'simple' life, single celled bacteria, but it was alive. More complex cells didn't start to form until about 1.5 billion years later. and multicellular life not until another billion or so years after that. Humans have been around about 1-200,000 years--a very short time period on this scale.

What we don't know: what was before the RNA world and how it came about. It may well have formed spontaneously from the nucleic acids already present through sequences of drying and wetting (which promotes the formation of the bonds and makes those polymers).

We don't know how the transition from the RNA to the DNA world happened.

We don't know when and in what roles proteins started being important for life. How much original metabolism was catalyzed by RNA and how much by proteins (like today)?

We don't know under what conditions the first life formed. Speculations include the ability of clay to promote certain reactions in the early stages, the chemistry to deep sea vents, and the cycles of drying and wetting that happen in small ponds.

On the other hand, we know a LOT more about the basic chemistry of life than we did 20 years ago. We know that nucleic acids can be produced in large enough quantity to allow for further reactions leading to RNA.

So, progress is being made, slowly but surely. There are still many questions, but we know more now than we did 20 years ago, and that was more than 20 years before that.

Thank you
U broke that down nicely

 

[Yazata]

Hi, Power Stone. Glad to see that you are still around.

"Scientists are not close to knowing the exact processes that took place on the earth which led to the origins of life. They may never know the exact answer because the evidence for this very primitive life has probably been destroyed by the more efficient life which evolved from it."

Yes, I think that's accurate.

Does anyone know of any theories as to why they don't know, or a way that could explain this in a little bit more detail?

Well, the Earth is thought to be approximately 4.5 billion years old. Life is believed to be at least 3.5 billion years old and perhaps as much as 4 billion or more years old.

Earliest known life forms - Wikipedia

So we are talking about things that happened a long time ago. The Earth is an active place, geologically speaking. Unlike the Moon which seems like kind of a museum of the early solar system, or Mars which once was Earthlike but kind of a frozen desert today. On Earth there's still active plate tectonics, there's all kinds of atmospheric weathering. There's mountains rising and being worn away again.

That means that very little of the Earth's original surface survives today. What little remains has been subject to all kinds of geological processes that might have obscured most of the traces of original life that might be present.

Keep in mind that the earliest Earth, back when life is thought to have originated, was a very unpleasant place. It was only recently consolidated from planetesimals in the Sun's very early accretion disk. According to some theories, it had just recently been struck by a Mars sized planet that knocked a chunk of Earth into the sky to become the Moon. And if that happened, it no doubt left the surface of the Earth molten and uninhabitable for some time afterwards.

Giant-impact hypothesis - Wikipedia

Then it's hypothesized that there was a period called the 'Late Heavy Bombardment' in which planet-killer asteroid impacts were a regular occurrance and probably kept everything churned up.

Late Heavy Bombardment - Wikipedia

I read that scientists theorize that RNA came before DNA.

Yes.

That's because DNA in cells primarily operates by directing the manufacture of proteins. The difficulty is that this is only possible with the assistance of enzymes, which are themselves proteins. So it's kind of chicken and egg problem. Enzymes couldn't have first been manufactured by DNA without enzymes already being present.

RNA neatly solves that problem, since RNA can not only store genetic information like DNA does, it can also function like an enzyme in catalyzing reactions. These RNA enzymes are called 'ribozymes'. The little nanomachines where proteins are manufactured in all of our cells today are called ribosomes and are partly composed of RNA. This is why ribosomes are thought to have been fundamental players in the origin of life.

RNA world - Wikipedia

I couldn't find anything Theorizing what came before RNA. Does anybody know if they have theorized something before RNA?

I don't think that anyone really knows. RNA is composed of nucleotides, and there's been lots of research into how these might have originated in conditions similar to those hypothesized to have existed on the early Earth. Then they are imagined to have come together somehow in sequences that were capable of self-replicating. Once we had chemical replicators, short strands of RNA in this hypothesis, we would have seen natural selection for the most efficient replicators. Then somehow (insert lots of speculation here) that resulted in the first simple cells. At some point we ended up with LUCA, the Last Universal Common Ancestor, the cell type from which all existing Earth life is directly descended.