Every now and then science comes up in the news. Since none of us at The Cool Ship are scientists, we turn to the one science-y person we know – Colleen’s husband, Mike Padgen. Mike is proud to be The Cool Ship’s resident non-expert and our Guy in an Unrelated Field.
So you finally got around to watching Prometheus when your wife was out of town. What did you think of it?
It was fine. I enjoyed a lot of it. It was well made, but the whole time I kept thinking, “When is this guy going to show up?”
The Ancient Aliens guy?
Yeah. It’s just such a silly show – “Why would these people have done this? How could this happen? Must’ve been aliens!” To make a serious movie using those ideas, it’s just boring to me. The possible answers to how life can come from non-life and, for that matter, what distinguishes life from non-life, are so much more fascinating than anything conclusions we could possibly draw by saying, “Must’ve been aliens!”
So then, if Ridley Scott is lying to us and it wasn’t aliens, how did life on Earth come about?
Well, it’s important to preface the rest of what I’m going to say with the fact that we will never know exactly how it happened on Earth. What we can know (even if they’re not fully understood as of yet) are plausible mechanisms by which the conditions on Earth 3.8 billion years ago (or so) would yield simple, self replicating life forms.
Life on Earth started 3.8 billion years ago?
Well, there’s no exact date, but it seems to have started soon after the Earth cooled enough to have liquid water on it, which happened when the Earth was only a few hundred million years old. Interestingly, the fact that life came about fairly quickly on Earth lends credence to the idea that life is common throughout the universe, even though we have no direct evidence of that.
So how could non-life become life?
The primordial soup, approximated in the famous Miller-Urey experiment, is not exactly right. One missing piece in that hypothesis is the lack of thermodynamic push – there is nothing pushing the ingredients in the soup to sustainably react with each other. Instead, it is thought that life originated in hydrothermal vents at the bottom of the sea, which provide both reactive hydrogen and a state of thermal disequilibrium that can drive the formation of complex molecules. The porous rocks in these vents contain small compartments that allow the organic molecules to accumulate, allowing further reactions to occur.
Since all life on this planet uses DNA to store genetic information, it is thought that the last universal common ancestor must have also had DNA. However, the very first self replicators could not have used DNA due to a chicken-and-egg type problem. The proteins that duplicate DNA are also encoded by that DNA. There is no selective pressure that would ensure that the genes responsible for duplication are maintained. It has therefore been posited that the initial life forms on this planet used RNA, which is able to catalyze its own duplication.
But where did the RNA come from?
Several organic molecules, including precursors of amino acids and sugar, can be formed in space and have been found on asteroids and meteors. The period before life arose, the Earth was bombarded with asteroids, so these interstellar organic molecules were delivered from space.
So it was aliens!
No, that’s not what I’m saying at all. These organic molecules form spontaneously in space, and with the right conditions on earth, can be organized into nucleic acids and proteins and all the other stuff life needs to exist. There is no infinite regression required.
Sounds like it was aliens.