Nick Lane thinks he knows how it happened, written up in his new book "The Vital Question: Why is life the way it is?".
Here is part of The Telegraph's review.
"The Vital Question ... consists of four parts: an exploration of the nature of life and living; a deep dive into life's origin and the emergence of cells; an account of how complex, or eukaryotic, cells arose and why sex and death are inevitable; and a final part that entertains some predictions as to life's future possibilities.I am in two minds about this book. Lane has a compelling and convincing story to tell, and what could be more important than to see how life could emerge from the inanimate through plausible stages?
There's a well-known saying in biology: "nothing in life makes sense except in the light of evolution". Lane might amend that to "nothing in life makes sense except in the light of energetics". The discoveries of the structure of DNA, the genetic code and all that follows have been vital in building a better understanding of life and how it changes over time. But no less important, Lane argues, is the discovery - once described as "the most counterintuitive idea in biology since Darwin" - that cross-membrane proton gradients power all living cells. This may sound like a technical detail until one considers the power it unleashes: almost incredibly, it is, per gram, a factor of 10,000 more than the sun. Further, the fact that this mechanism is conserved across all life has vital implications for its origins, constraints and possibilities.
Lane works through these implications. He hypothesises that life originated at alkaline vents at the bottom of the ocean as early as four billion years ago. Lane and his colleagues have previously published on this subject in Nature magazine. Here it is set out with compelling clarity for the general reader.
He then explores the evolution of the eukaryotic cells that form all animals, plants, fungi and algae. "I challenge you to look at one of your cells down a microscope and distinguish it from the cells of a mushroom," writes Lane. "They are practically identical. I don't live much like a mushroom so why are my cells so similar?"
The answer, he argues, has a lot to do with our shared dependence on mitochondria, tiny organelles inside each of our cells that act like batteries, and which are descended from a bacterium that was once swallowed but not consumed by an archaeon. Lane argues that this union and subsequent symbiosis was a freak event. It took place only once, giving rise to virtually every living thing we can see.
Lane concludes that complex life is likely to be rare in the universe — "There is no innate tendency in natural selection to give rise to humans or any other forms of complex life," he writes. "It is far more likely to get stuck at the bacterial level of complexity." He adds that he cannot, however, put a statistical probability on that."
But that little biochemical nanomachine called a cell is very complex, much more complex than a car engine. You do have to delve into the details of the piece-parts to engage with this subject. For people without any background in cell biology how easy is that? It's the same problem in all areas of fundamental science: understanding isn't a simple extrapolation of everyone's common sense and experience - you really do have to learn something first and to concentrate.
So I doubt that all the people who generically 'would like to know how it is that life can get started on a planet' will actually engage with and complete this book. But with some degree of persistence (and, to be fair, some background) there is no end to the revelations in Nick Lane's analysis. I was reading along while periodically muttering under my breath things like 'Wow! So that's why we age.'
So recommended for those who really do want to know: you will finish the book and the world will be a different place.