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May 22, 2020 18 tweets 7 min read Read on X
It's #WorldBiodiversityDay today! The complexity of life is amazing, but also begs one question: what did the first life form on Earth actually look like?

Let's find out... #FridayMotivation Image
Now there's no universally agreed definition of life: even Erwin Schrödinger was uncertain what it was. But an ability to resist entropy, to reproduce, to mutate, to have a metabolism and to self-organise feature in most definitions.
And whatever life is we reliably assume it's all interlinked in some way. We still use the medieval idea of a 'tree of life' to map the connections and currently scientists believe this tree has either two or three fundamental branches. Image
Bacteria and archaea form two of these fundamental branches: both are simple single-cell organisms that usually lack organelles, but their ribosomal RNA is very different. They also form the bulk of the biomass on the planet.
Eukaryotes are different: they have membrane-bound organelles such as mitochondria and form multicellular organisms such as you and I. So fid they evolve from archaea, or are they a third fundamental branch of the tree of life? Image
Views vary on this, and it's due to horizontal gene transfer. You don't just inherit your genes from your parents, you can also swap them with your neighbors! That's how bacteria share antibiotic resistance, and viruses can help it happen. Image
But it also complicates the tree of life, making it hard to tease out who was related to whom in our prehistory based on gene sequencing. Maybe it's best to talk about a mosaic of life instead of a tree. Image
This hasn't stopped biologists trying to discover LUCA: the last comon universal ancestor of all living things. Gene analysis of multiple bacteria and archaea suggest there are 355 common protein clusters across all life, which give us a clue as to what LUCA may have looked like.
LUCA was possibly an anaerobic organism that lived in ocean hydrothermal vents, places rich in H2, CO2 and iron. The energy gradient between the warm vent and surrounding colder water allowed LUCA to make adenosine triphosphate - the molecule that allows energy transfer in cells.
This means LUCA, like a virus, was an organism on the edge of life. It possibly had no cell membrane and relied on iron to form its boundaries. LUCA was a fizzing undersea rock using its unique environment to create energy. Possibly.
The ability for organisms to generate their own energy gradients evolved later on, allowing life to break away from the vents on at least two occasions – one giving rise to the first archaea, the other to bacteria.

But the story has one big flaw...
It's based on working backwards from organisms that currently exist. What about the extinct ones? Plus LUCA is still a complicated organism. How did this complexity come about? What was before LUCA? Image
Well in 1992, in a water tower in Bradford being tested for Legionnaires disease, scientists found an amoeba which contained a starting secret...

It was infected with a giant virus!
Viruses are normally small, but Mimivirus - as it came to be known - was a monster. It was big enough to be seen under a normal microscope and its genome was far bigger than it needed to be for a virus, with almost a thousand protein-coding genes. Image
Since 1992 a number of other scary sounding giant viruses - Pandoravirus, Megavirus etc - have been found. Stranger still these can themselves become infected by other, simpler viruses. So what's going on? Image
Well there are two theories about giant viruses. One is they grew from simpler viruses by capturing DNA from host organisms. They may be huge but that's just accidental; their big genome doesn't really mean anything.
The other theory is they evolved from complicated organisms which lost their ability to reproduce themselves. What's fascinating is that these initial organisms may not have been bacteria or archaea - instead they may have been earlier types of life which are now extinct.
The good news is that giant viruses only attack amoebas. But are they evidence of a lost fourth domain of life? Many are skeptical, but the more examples we find the more we learn about the earliest life on Earth and how it may have developed.

Happy #BiodiversityDay everyone!

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More from @PulpLibrarian

Nov 22
Today in pulp I'm looking back at one of the greatest albums of all time.

What are the chances... Image
By 1976 Jeff Wayne was already a successful composer and musician, as well as a producer for David Essex. His next plan was to compose a concept album. Image
War Of The Worlds was already a well known story, notorious due to the Orson Wells radio play production. For Wayne it seemed like a great choice for a rock opera. Image
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Nov 17
Shall we take a look at some classic pinball table backglass art?

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Star Trek pinball (Bally, 1979). Image
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Nov 12
Today in pulp I'm looking back at a very popular (and collectable) form of art: Micro Leyendas covers! Image
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Nov 9
Today in pulp: what makes a good opening sentence for a pulp novel?

Now this is a tricky one… Image
The opening sentence has an almost mythical status in writing. Authors agonise for months, even years, about crafting the right one. Often it’s the last thing to be written. Image
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Nov 7
The Time Machine, Brave New World, 1984: these weren’t the first dystopian novels. There's an interesting history of Victorian and Edwardian literature looking at the impact of modernity on humans and finding it worrying.

Today in pulp I look at some early dystopian books… Image
Paris in the Twentieth Century, written in 1863, was the second novel penned by Jules Verne. However his publisher Pierre-Jules Hetzel rejected it as too gloomy. The manuscript was only discovered in 1994 when Verne’s grandson hired a locksmith to break into an old family safe. Image
The novel, set in 1961, warns of the dangers of a utilitarian culture. Paris has street lights, motor cars and the electric chair but no artists or writers any more. Instead industry and commerce dominate and citizens see themselves as cogs in a great economic machine. Image
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Oct 31
Time once again for my occasional series "Women with great hair fleeing gothic houses!"

I assume everyone's doing it this #Halloween ? Image
The Legend Of Crownpoint, by Monica Heath. Signet Books, 1974.

A lot of moss on that heath... Image
The Legend Of Holderly Hall, by Kate Cameron. Leisure Books, 1974.

This is number one in a series of four novels, proving that nobody really reads Trip Advisor hotel reviews... Image
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