An organism has been found that photosynthesises from light coming from hydrothermal vents 2400 metres below the sea. It is the first photosynthetic organism discovered that does not rely on sunlight.
As reported in a paper pithily titled ‘An obligately photosynthetic bacterial anaerobe from a deep-sea hydrothermal vent’ published in the journal of the Proceedings of the National Academy of Sciences, the green sulphur bacteria was found living near a thermal vent off the coast of Mexico called 9 North.
One of the paper’s authors is Professor Robert Blankenship from Arizona State University’s chemistry and biochemistry department. In an interview with Skip Derra (posted on the university’s website) , Blankenship said the bacteria uses a chlorosome complex which acts like a satellite dish to collect any light it can and transfer it to the organism’s reaction centre where the photosynthesis takes place.
Blankenship also said the discovery was important not just for what it meant for life on earth, but what it means for the search for life outside of Earth.
‘This shows that photosynthesis is something that is not limited only to the very surface of our planet,’ he says. ‘It lets you consider other places where you might find photosynthesis on Earth, as well as on other planets.’
As the original paper’s abstract reflects:
‘The abundance of life on Earth is almost entirely due to biological photosynthesis, which depends on light energy. The source of light in natural habitats has heretofore been thought to be the sun, thus restricting photosynthesis to solar photic environments on the surface of the Earth. If photosynthesis could take place in geothermally illuminated environments, it would increase the diversity of photosynthetic habitats both on Earth and on other worlds that have been proposed to possibly harbor life.’
Something for us science fiction writers to ponder.
Another amazing aspect of this paper is its relative obscurity: the paper was published in June 2005. If not for the heads-up in a recent post by Jerry Coyne on his website Why evolution is true, I doubt I would ever have learned about it.
It was a cold, clear Tuesday night. Harrie ate her dinner so quickly she was done by the time Maggie and Rachel were still munching on their third forkful.
‘I don’t think we gave her enough,’ Rachel said.
‘Do you want more dinner, Harrie?’ Maggie asked.
Harrie shook her head, but wasn’t looking at either of her mothers. She was staring out the window behind them. The sun was down and only a pink light softened the horizon. Just above, where the pink became violet, she could just make out the twinkle of Venus, the evening star and the first light to appear in the night sky. It was one of her favourite things to look at with her telescope – but tonight she had other plans.
‘Are you sure you don’t want more food?’ Rachel asked, looking over her shoulder to see what Harrie was gazing at. ‘Remember, it’s a full moon tonight and it will be so bright it will be hard to see anything else.’
Harrie nodded. ‘I know. That’s why I want go out. I want to look at the moon.’
‘That’s a good idea,’ Maggie said. ‘You haven’t looked at it through your telescope for some time; you’ve been too busy with Jupiter and Mars and Orion’s Belt – ’
‘Twenty-two nights ago,’ Harrie said, her voice very definite. ‘And point-two.’
‘Point two?’ Maggie asked.
‘Twenty-two-point-two nights ago.’ Harrie’s face scrunched up in thought. ‘Can you have a point-two night?’
Her mothers shrugged at the same time. ‘I guess,’ Maggie said. ‘You sound very sure of yourself, though.’
‘Uh-huh. The last time I looked at the moon through my telescope was when it was in its last quarter, and that was twenty-two-point-two nights ago.’ Harrie took a deep breath: that sentence was long even for her.
‘When does it come up?’ Rachel asked.
Harrie pointed to the side of the house opposite the window. ‘It should already be up. But the best time to see it will be … ’ Her voice trailed off and her face scrunched up in thought again. She moved her dinner plate out of the way, stretched out her arms and placed her straight hands on top of one another, palms inward. ‘That’s twenty degrees and the moon moves half-a-degree every hour and the moon is about here and the best time to see it is when it’s here … ’ She wiggled fingers to show exactly where the moon was each time she mentioned it.
‘So the best time to see it is when it reached the little finger on your right hand,’ Rachel observed, smiling slightly.
Harrie nodded, taking another deep breath.
‘You are very clever,’ Maggie said matter-of-factly.
Harrie sighed. ‘Yes,’ she agreed, as if it was a burden.
‘So, just to make sure I understood what you’re saying,’ Rachel said, ‘the best time to see the moon is about half-an-hour from now?’
‘That’s about your bed time.’
‘Hmm,’ both mothers said at the same time.
‘But it has been twenty-two-point-two nights since I saw the moon with my telescope,’ Harrie pointed out reasonably.
Maggie and Rachel looked at one another. ‘True,’ Maggie said.
‘And in the life of five-year old, twenty-two nights is quite a long time,’ Rachel added.
‘Not to forget the point-two,’ Maggie pointed out.
The mothers fell silent as they considered whether or not to let Harrie stay up past her bedtime.
‘We could ask Banjo what he thinks,’ Harrie suggested. ‘Banjo?’
A young black-and-tan kelpie bounced into the room with more haste than dignity as his back paws skidded out from underneath him and he ended up sliding on his bum for the last two metres. He came to a stop right next to Harrie and gazed up at her adoringly, as if the whole tangled, embarrassing entrance had been planned.
‘One day he’ll grow into those large paws of his,’ Rachel whispered to Maggie. ‘Hopefully.’
‘Banjo, I have an important question for you,’ Harrie said, solemnly meeting the dog’s gaze.
Banjo barked once. Everyone in the family knew that meant ‘yes’, except when it meant ‘no’.
‘Do you think I should stay up late so I can see the full moon in my telescope?’
Again, Banjo barked just once, and Harrie turned back to her mothers. ‘See?’
‘Well, no arguing with that,’ Rachel said.
Maggie let out a small sigh. ‘All right, but just this once. You are not to take this as permission for you to stay up every time you want to go out and look at the night sky.’
‘Maybe once every twenty-two days?’ Harrie suggested.
‘Don’t push it, kiddo,’ Maggie said. ‘Now go and get some warm clothes on. The last thing we need is for you to freeze out there.’
Harrie grinned at her mothers as she left the table, then hurried to her room, eagerly followed by a scurrying Banjo who this time somehow managed stay upright on all four paws.
Although winter was officially over and spring had sprung, Harrie’s home town was high up in the mountains and it got cold there when the sun was down. But it did make for spectacular nights, when the stars and the planets danced across the black velvety sky.
Harrie loved looking up at them even when she didn’t have a telescope, but now that she could see them up close the night sky seemed twice as special. And the most special thing in the whole universe to see with a telescope was the Moon.
The first time she had looked through the eyepiece and the Moon suddenly swung into view it seemed to jump right out at her and she forgot to breathe for a long time, and when she finally did breathe out it came in a great big gush.
Harrie never got tired of looking at it. She knew all the big craters now – like Copernicus and Kepler – and all the big seas – like the Sea of Nectar and the Sea of Islands. But most especially she knew the Sea of Tranquility, because that is where the first humans who walked on the moon landed their spaceship, called the Lunar Module.
The night was getting colder and colder. But Harrie didn’t feel it. Even Banjo was getting cold, and tried snuggling up against her legs, almost tipping her over. But Harrie didn’t care. Her mothers were softly calling to her to come back inside. But Harrie didn’t hear them. Staring through her telescope at that great white globe with all its craters and seas and mountains was more important than being warm or going to bed.
One day I’ll go there, she thought. One day I’ll go the Sea of Tranquility and touch the dark soil and then look up and see Earth, and with my telescope I’ll find home and wave at my mothers and Banjo and everyone else I know.
Maggie tapped her gently on the shoulder. ‘It’s time, Harrie. We’ve let you stay up for a long while. Come inside now. Your cheeks are as hard and cold as ice.’
Slowly she drew back from the telescope. When she looked up into the sky again the Moon was still there but much smaller.
‘Still pretty,’ she said, ‘no matter how big it is.’
Maggie and Rachel stared up at the Moon as well. Even Banjo, who was wondering what everyone was staring at that seemed so interesting. There wasn’t a rabbit to be seen anywhere.
‘Look!’ Harrie said, pointing at the soft nebula of light that surrounded the Moon. On either side of it was a little light. ‘Are they planets or stars?’
Maggie laughed. ‘I’ve heard of them but never seen them before.’
Rachel and Harrie looked at her expectantly. ‘What are they?’ Harrie asked.
‘They’re called Moon Dogs. It’s so cold up there that the light from the Moon is being caught by ice crystals. They almost look like miniature moons, don’t they?’
Harrie sighed, a deep and immensely satisfying sound. She patted Banjo on the head and started back the house, the moonlight shining in her hair and on his fur.
She stopped for a second, looked back up at the sky, and said, ‘Look Banjo, Moon Dogs.’
Banjo barked once, meaning, ‘Yes, what else would they call them?’
This blog post is titled ‘When did humans first leave Africa?’ I confess, it’s a trick question, but we’ll come back to that later.
So to start with, let’s attempt to answer not a trick question but a trickier question: when did Homo sapiens first reach Australia?
This has been a contested debate for several decades, with proposed dates stretching from 75,000 years ago to 40,000 years ago. The bottom mark was established by the dating of the remains of Mungo Man, the oldest remains of anatomically modern humans (AMH) yet found outside Africa.
Towards the upper end, luminescence dating of sediments around artefacts recently found at Madjedbebe in the Northern Territory give a date of around 65,000 years, although this is contested.
In a recent article in The Conversation, ‘When did Aboriginal people first arrive in Australia?’, authors Alan Cooper, Alan N. Williams and Nigel Spooner state the ancestors of Aboriginal Australian first reached Australia sometime between 50,000 and 55,000 years ago, just after AMH left Africa.
‘All non-African individuals studied so far contain around 2% Neanderthal ancestry, suggesting that admixture mostly occurred shortly after the dispersal of anatomically modern humans from Africa … the date of hybridization has been estimated to be approximately 50–65 kyr ago …’
Cast of H. neanderthalensis (Amud 1) from the Australian National University. Photo: Simon Brown
This date is now generally accepted by palaeoanthropologists.
But that presents us with a quandary. As I wrote in an earlier blog, fossils from the cave of Jebel Irhoud in Morocco, together with genetic data from a 2,000 year old Khoe-San skeleton, suggests our species arose in Africa at least 300,000 years ago. So why did it take our species a quarter of a million years to find the exit?
Well, as it turns out it, it didn’t.
In a January 2018 report in Science, authors Chris Stringer and Julia Galway-Witham note that recent fossil evidence from Israel suggests our species had left Africa by 180,000 years ago. The report also recounts genetic analyses of Neanderthal fossils from two caves, Denisova in Russia and Hohlenstein-Stadel in Germany, that ‘indicate at least one earlier phase of introgression, from H. sapiens into Neandertals … estimated at 219,000 to 460,000 years ago’.
At this stage, it seems that AMH could have left Africa over 200,000 years ago, and yet DNA evidence strongly suggests the ancestors of all non-African members of our species left Africa no earlier than 60,000 years ago.
So what’s going on?
Nielsen et al. write that the latter date indicates when the ‘ultimately successful’ dispersal of H. sapiens from Africa occurred. In other words, those members of our species who left earlier are now extinct and left no trace in our genetic record.
Stringer and Galway-Witham write that there is evidence there were several humid phases between 244,000 and 190,000 years ago. But these phases were bracketed by severe periods of aridity, which meant ‘the region was probably more often a “boulevard of broken dreams” than a stable haven for early humans.’
Chris Stringer, Research Leader in Human Origins, Natural History Museum
On the other hand, a letter published in Nature in 2016 suggests that earlier migrations of H. sapiens from Africa may have left their mark on some of us after all; specifically, Papuans.
After analysing ‘a dataset of 483 high-coverage human genomes from 148 populations wordwide … ‘ Pagani et al. found ‘ … a genetic signature in present-day Papuans that suggests that at least 2% of their genome originates from an early and largely extinct expansion of anatomically modern humans … out of Africa.’
This brings us back to the article in The Conversation. Cooper et al. discuss how Aboriginal Australians moved to and occupied Australia around 50,000 years ago. Of course, 50,000 years ago it wasn’t Australia, it was Sahul, a single landmass comprising Australia, Tasmania and Papua New Guinea.
Yet the letter in Nature suggests that Sahul might in fact have been occupied by H. sapiens before that date. Its authors hypothesise either that these people came from an unsampled archaic human population that split from modern humans ‘either before or at the same time as did … Neanderthal’, or that they were a modern human population that left Africa ‘after the split between modern humans and Neanderthals but before the main expansion of modern humans in Eurasia’.
The data from all this research is sometimes confusing and contradictory. Over the last quarter century palaeoanthropology has undergone a great revolution driven partly by discoveries of new hominin fossils (eg H. floresiensis and H. naledi), and partly by new and refined techniques in analysing DNA. There is a lot of data to sort through, doublecheck and assess. Nevertheless, as measurements are refined and new discoveries are made, we learn more about our past and so more about ourselves.
So, why is the header a trick question?
All the above information deals with the history of just one species, our own. But H. sapiens were not the first humans to leave Africa. For example, some members of H. heidelbergensis left Africa around half a million years ago, evolving into H. neanderthalensis in Europe. Those that remained in Africa almost certainly gave rise to H. sapiens.
And if the conclusions of a recent paper by Argue et al. studying the phylogeny of H. floresiensisis are correct, then another and possibly earlier human migration out of Africa occurred. This species’ forebears are closely related to H. habilis, the oldest species in our genus, Homo.
It’s almost as if the need to migrate is as defining a feature of our genus as bipedalism, a large brain and an opposable thumb.
Pluto as seen by New Horizons. Image credit: NASA/JHUAPL/SwRI
AJ and I ducked out of the house on the night of August 11 to have a quick wine or two at King O’Malley’s pub in the city. When we got there we discovered the place had been invaded by Science in the Pub, and the two of us spent a pleasant hour drinking white wine, eating free food, and watching a slide show about the New Horizons mission to Pluto.
What’s more, it was a presentation hosted by John Berry, the American ambassador to Australia, and featured Nobel prize winner Brian Schmidt from the ANU, science communicator and astrophysicist Alan Duffy from Swinburne University of Technology, and Glen Nagle, Education and Outreach Manager at Canberra’s Deep Space Communication Complex at Tidbinbilla.
It was a pretty crowded affair and the screen was sometimes obscured by jostling customers, excited science addicts and through-traffic, but the mood was positive and the atmosphere … well … sciencey. (If this isn’t a word already, I bag naming rights.)
What follows are some of the amazing facts we learned about the New Horizons mission and Pluto, plus a few extra tidbits.
The mission was launched on 19 January 2006, when Pluto was still classified as a planet. Eight months later it was demoted to a dwarf planet. Furthermore, in 2006 only three moons had been identified orbiting Pluto. Before the probe reached its destination, we knew of five moons.
The probe’s closest approach to Pluto occurred nearly nine months after launch, on 14 July 2015, and after a journey of approximately 7.5 billion kilometres. Disappointingly, New Horizons was 7.5 seconds late for its appointment.
Still, not too bad when you consider that to travel the same distance travelling at a highway speed of 100 kph, it would take you around 8,560 years. In other words, to arrive in 2015 you would have had to start driving about the same time the world’s first city walls were being built around Jericho.
Shots of Pluto’s night side were made possible because of reflected sunlight from Pluto’s largest moon, Charon.
Pluto’s atmosphere expands as its eccentric orbit brings it closer to the sun, and then freezes when Pluto recedes from the sun. Since its last closest approach to the sun in the 1990s, Pluto’s atmosphere has halved. This was confirmed by a radio signal sent from Earth to New Horizons through the atmosphere when the probe reached the other side of Pluto. The signal had to hit a piece of equipment about the size of a credit card, and enabled scientists to measure the signal’s radio occultation.
Scientists were surprised to discover that ultraviolet light broke up some of the methane in Pluto’s atmosphere create more complex hydrocarbons such as ethylene and acetylene. They were even more surprised to learn that about 50% of this UV comes not from our sun, but from other stars.