Life on Earth is something we take for granted sometimes. But like our planet, there was a time when it simply did not exist. Abiogenesis is the scientific name for the origin of life.
Life is Hell
Around four and a half billion years ago, the Earth formed. At that time, Earth was a hunk of hot rock, with volcanic eruptions and meteor impacts generating a first, toxic, atmosphere. The temperature was much higher than now and the mixture of sulfur and water in the atmosphere was slightly acidic.
During the next two hundred million years, actual oceans formed as the temperature went down. They also became less acidic. Not that Earth was a fun place at the time. The sun bombarded the planet with UV radiation, plate tectonics were in overdrive, leading to many volcanic eruptions, and to top it off, every so often large chunks of rock — up to 500 kilometers in diameter– would crash down on our planet.
Despite this violence, sometime between 4.2 and 3.5 billion years ago, something magical happened in the depths of the ocean. Well, most likely it did. Information about the period is scarce. Deep below the water’s surface, hydrothermal vents spewed hot vapor from the volcanic crevices. It turns out, the conditions around hydrothermal vents are good for creating complex organic compounds. The depth also protected these compounds from the radiation and impact events on the surface.
It’s an RNA world after all
‘Complex organic compounds’ is not the same as ‘humans and animals’. It’s just what it says: carbon-based molecules that have a more complex structure than what came before.
However, the transition to life as we know it requires more steps. Life these days is made up of self-replicating cells. Cells consists of a core surrounded by a membrane to protect that core. But that did not come about out of thin air (or deep ocean).
The first proto-organic molecules around air vents evolved slowly. The hypothesis goes that, at first, they floated freely, replicating and using each other’s properties, because there were no membrane protections. Darwinist evolution had not really started yet. It was an RNA world.
The RNA world transitioned to one where proteins formed, the RNP World. Then DNA and cell membranes came around, kickstarting evolution and eventually bringing about the world we know today.
From DNA to dinosaurs to us
Cells started to evolve into various life-forms. Photosynthesis came half a billion years later and slowly more complex life evolved. And by slowly, I mean, it took some two billion years to get from single-celled life to multi-cellular life.
Molluscs and anthropods appeared, diversifying until the seas were filled with all kinds of weird things. Then, algae decided to get up and leave the sea, leading to surface bound plants. Later, animals followed suit. Reptiles evolved, but then disaster struck.
An extinction event happened about 250 million years ago. It wiped out most life on Earth. It did lead to the rise of a new type of reptile: the dinosaur.
Dinosaurs ruled the Earth for a long while, until the dinosaurs went the way of the dinosaur and died out in another extinction event 66 million years ago. And so both ends of the dinosaur age are marked by extinction events, the end probably an asteroid impact, the start quite possibly as well.
Yet, that does bring us to the rise of the mammal, which led to the current pinnacle of life: humans. Now, I wouldn’t say humans are the end of evolution, but we are the most successful species to walk this planet so far – depending of course on your definition of success. We’ve done things to atoms you can hardly believe, we’ve traveled to the moon. There are carts on Mars and probes in interstellar space.
That doesn’t mean we’re perfect, far from it. We are also the first species who is well on its way to organize their own mass extinction event, and only after having been around a few hundred thousand years, not millions or billions.
The above is the briefest description of a process that took billions of years. Books can and have been written about this subject, that cover it far better. I find it endlessly fascinating, though.