Retinas reveal future health, and the first cells on Earth

The origin of life on Earth - and beyond - is a mystery, and, arguably, one of the most important questions to answer. We know that life started simply, probably with self-replicating chemical reactions most likely based around something similar to the DNA molecules we rely on to carry our genetic code today. But, pretty quickly, those reactions found a way to wrap themselves up inside oily membranes that could protect them from the surroundings and make the process more reliable and efficient. Hey presto, the cell was born. But where did those membranes, made of fatty acids, come from in the first place? That question has bothered biologists for decades. Now, though, researchers at Newcastle University have recreated in the lab the conditions around hydrothermal vents, also known as underwater black smokers. These conditions, Jon Telling has found, can spontaneously generate the very molecules that scientists have been searching for…

Jon - There's a few lines of evidence that point towards these hydrothermal vents, these hot springs, as a likely place for where life originated. People have tried to find out what the earliest cell that everything originates from was like, and what they've deduced from looking at the genes is that the first cell - known as the 'last universal common ancestor' - liked it hot, it probably lived off hydrogen gas, and it would've used carbon dioxide as well to build itself. So those lines of evidence all point towards these hot springs as a possible place for the origin of life.

Chris - It sounds like we actually know quite a bit in terms of what we expect that ancestor to have been like. But what was the outstanding question you were trying to crack with relation to it, then?

Jon - Previous people have tried running different experiments to try and mimic some of the conditions that these hydrothermal vents would've had. People had either tried to recreate, say, the high temperatures or the high pressure, or the kind of continuous flow where you're mixing seawater with this hotter fluid, but nobody had really gone on trying to combine all of those at once. That's what we wanted to do. We built some new apparatus in our lab to try and get that; the high pressure, get the high temperature, and get the continuous flow all in one experiment and try and react this hydrogen gas and this carbon dioxide over these metals to see if we could generate organic molecules.

Chris - What source of molecules were you looking for?

Jon - Ones we were particularly interested in were these molecules known as fatty acids. They have a fatty end and a water loving end. The interesting thing about them is, if you get enough of them in that water, then they can form what are known as these membrane structures, vesicles or liposome sometimes they're known as, but they basically form these little round balls surrounded by a membrane which separates what's in them from what's outside. So it is acting in a way as a sort of first cell membrane, potentially, which could separate the external environment from the internal and let different chemistry happen.

Chris - I understand where you're going with that because obviously that was the big question, wasn't it? If life gets started as a series of chemical reactions, where did cells come from? So if you've got a reaction that can produce the oily bags that surround all our cells, that is 90% of the equation.

Jon - Well, it's certainly a good step forward. It's the first step to creating a self, something different from what's outside. The ability to do that and then concentrate chemicals differently to outside, generate different reactions, would've been I think an essential step for how life started.

Chris - What are the raw materials that you are feeding into your pretend hydrothermal vent and what chemicals did you see coming out at the end in these conditions that lead you to think that is possibly how some primitive cell like structures could have formed?

Jon - What we fed in, the basis of it was hydrogen gas which we added under pressure. Then, we combined that with dissolved carbon dioxide. We're reacting them over a mineral, in this case an iron rich mineral known as magnetite, to form hydrocarbons: organic molecules. In particular we were looking for these fatty acid molecules, which are a type of hydrocarbon.

Chris - And do you get many and how quickly?

Jon - The experiments we've run so far, we only ran for 16 hours and in that time, yeah, we generated enough to find them. If we run it for longer, we might find that we generate even more of them, but there are certainly enough of these organic molecules for us to analyse.

Chris - Do they start to self assemble? Because the point you're making is that the fatty bits love other fatty bits, so they tend to get together. So do you start to see that happening?

Jon - As yet, no, because when they form they actually form on the mineral surface. The next stage of experiments that we want to do is to try and do this: to actually change the chemical conditions. We think there may be, if we make the environment more alkaline, we can get some of these molecules, particularly these fatty acids, to lift off and hopefully we could then see them self-assemble.

Chris - If we bring what you found to the party that already people had envisaged as to how life could have got started, how do you bring and unite your discovery of how these fatty acids begin to form with what people thought might also be going on around the same time, about 4 billion years ago, that was the start of life?

Jon - People have found these reactions going on at higher temperatures, for example, before. What we've done is do these experiments under more realistic conditions as to what the conditions may have been like on the early Earth. And it just gives that greater likelihood, I think, that these really important organic molecules may well have been formed within these sub ocean hydrothermal vents. And it might also increase our understanding as well, I think, about how life may have originated in other places in our solar system, or whether a similar chemistry might be going on.

Chris - I was going to ask you about that because of course we've got missions that are going to be looking at Europa, which is one of Jupiter's moons. People have also considered Enceladus, one of Saturn's moons, which appear to have warm liquid oceans beneath the surface of ice. So it's possible the conditions there might be similar to the conditions you are mimicking in your laboratory?

Jon - Exactly. I think the best characterised ocean so far is actually Saturn's moon Enceladus. There's actually a spacecraft which has travelled around, known as Cassini, and it's actually sampled these plumes which people think are emanating from beneath the icy layer of Enceladus into this ocean. So you've got part of this ocean actually being blasted out into space and been analysed, and when they've analysed the vapours and particles that are in this plume, they found hydrogen gas, they found carbonates - so signs that carbon dioxide there as well. And they've also analysed different organic molecules. It seems that all the ingredients, potentially, for an origin of life might be there, but it's going to take a fair few more experiments to try and narrow that down further.

Researchers in the United States have made a big splash in the science field this week by using ultrafast photography to watch what happens when pond skaters - also called water striders in America - are hit by falling raindrops, which massively outweigh the tiny insects. For them, it’s like one of us standing under Niagara Falls, says the study’s author at Florida Polytechnic University, Daren Watson…

Daren - We did this by first capturing the insects from our local ponds and we had to create a rainfall simulator. So we had a reservoir of water that we pumped through a nozzle that mimicked raindrops. Those raindrops struck the insect, and we observed the interaction using our high speed video cameras in the lab.

Chris - So you gave them a shower basically? <laugh>. How fast is fast? When you say high speed imaging, how many pictures a second are you taking of this?

Daren - We can capture up to 4,000 frames per second, so it's very fast. We see the droplets move in on the order of milliseconds.

Chris - Talk us through then, when you look at this footage, what does it show?

Daren - Before we talk about what occurs with the insects, when a raindrop hits a pool of water, what you're going to get is a splash. And we are all familiar with splash. We see this during rainfall, but that splash constitutes a couple different phases. So we see an underwater crater, we see a jet that goes back up above the water surface. And it was important for us to look at how the insect interacts with these different components of the splash. So when the insect is struck by a raindrop, we see that the raindrop pushes the insect into the water body and the insect. You'll find that along the inner surface of that particular raindrop as it creates a crater inside the body of the water. So we find that the insect is, you can say, attached to the water at that point in time. So then when the jet is formed, it is transported out of the water with the jet.

Chris - So the water gets pushed downwards and outwards and compressed by the incoming droplets. And what is a rebound of the water coming back underneath the insect that creates almost like a geyser underneath it that pushes it up in the air?

Daren - Yes. The rebound occurs as the dented surface of the water tries to go back to its original state. So raindrop pushes the insect beneath the water, and then there's a rebound and you have the jet coming upwards.

Chris - Does the action stop there or do you then get secondary effects? Because obviously what goes up must come down. If you've made a jet, do you then get secondary rain effectively off the back of having hit the insect the first time?

Daren - Yes. And that is where the danger lies for the insect because that jet then disintegrates to create what you would've termed secondary rain. And it then pushes the insect inside the body of the water again. And we find that the rebound is going to be so precipitous that the insect is going to be left beneath the waterline.

Chris - Does it have to swim up? And then how does it break through, assuming it does, the surface of the water? Because there's surface tension there between the air and the water isn't there. So how does the insect get back through there and end up on the air side rather than on the water side?

Daren - This is rather innate. So the insect, because the insects are generally born beneath the waterline and their youngs, what they do is they swim to the top to where that waterline is and they break the surface to get onto the airside. So the adults are also able to do that. And they do that through a series of what we call power strokes, applied at an acute angle. And that allows the insect to be able to break that waterline to get back onto the air side of things.

Chris - They obviously do it quite well because there's loads of them. And if I look at the pond near where I live, there's many, many to count. So they're obviously pretty good at this, especially with the terrible weather we have. But what are the applications of this? Because it's interesting and fascinating to understand how these insects have evolved to have this behaviour, but understanding this now as you do, can you apply it to any other aspects of what we see in the marine or aquatic realm?

Daren - Yes, we can. Our results here will allow us to better understand the transport of floating particles like microplastics on the Earth's water bodies. Now microplastics are similar in size to water striders or in your case pond skaters. And they would likely share a similar experience during rainfall. As a matter of fact, in some of our experiments, we replaced water striders with floating particles and observed these similar interactions. So that's the main real world application of the study at the moment. And we're going to be seeking to explore transport of microplastics on our world water bodies going forward.