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SciShow Space explores new theories about the timing of the development of life on Earth, and elsewhere in the universe.
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When we talk about the search for life elsewhere in the universe, we almost always talk about it in terms of 'where'.
Like, where other habitable planets might be, and how far they are from their stars and whether we could ever reach them.  All that stuff is fun to think about, but some scientists are investigating the issue of extraterrestrial life by asking a different question: When? Because even if life has developed on other planets, it may not have shown up at the same time as it did here.  

Let's start with what we know.  Earth is about 4.5 billion years old, and the fossil record shows that the first hints of simple single-celled organisms appear around 3.7 billion years ago.  Over time, life forms became increasingly complex, with the first signs of multi-cellular organisms showing up in fossils that are around 1 billion years old.  

Since then, life has grown in complexity at an exponential rate, creating the diversity that we see today.  In fact, a pair of theoretical biologists, Alexei Sharov and Richard Gordon recently calculated that the genetic complexity on Earth has been doubling every 376 million years.

That means that today, there's twice as much unique information encoded in the genomes of living things as there was 376 million years ago, and four times more than 752 million years ago, and so on.  And this got the scientists wondering... what if they extrapolated their trend backward?

If the genetics of living things doubled in complexity every 376 million years, then when would the very first simplest form of life have appeared?  Much to their surprise, they found that, mathematically speaking, the first genetic ancestor to all life on Earth should have existed 9.5 billion years ago, 5 billion years before Earth actually formed.  

Now, the scientists point out that there are explanations for this. Like, it's possible that life on Earth grew more complex, more quickly in the past than it does now, which would account for their results. But still, it raises the question: what if life as a thing in the universe is older than our planet itself?  

Sharov and Gordon aren't the only ones thinking about when life began.  Astrophysicist Avi Loeb recently calculated that what we think of as the general formula for life - liquid water, chemical compounds like methane and ammonia, and a rocky planet to serve as the cosmic mixing bowl could have all formed more than 13.5 billion years ago, as early as 10 million years after the Big Bang. 

At that point in time, Loeb figures there were probably some planets, most likely rogue planets, not bound to any star, formed from the cast-off debris from the very earliest stars in the universe that had already exploded.

And those planets wouldn't have even needed nice, balmy orbits around a friendly star to get the spark of life out of their chemical mixtures. 
That's because the universe started off extremely hot and has been cooling ever since.

So at some point, he says, the average temperature of the universe was in the right range for those rogue planets to have liquid water on their surface. Nutty, I know.

But, studies like these suggest that life could be older than we think and that it could naturally spread from place to place around the universe - a theory known as panspermia. 

According to this theory, impacts could blast material of the surface of a planet and that debris could carry with it the ingredients for life. 
And if it kicked out fast enough, some of that material could eventually end up on other planets. 
In this scenario, simple components of life from rogue planets could have been mixed in with the material that our Solar System formed from billions of years ago. 

So, I'm not saying it's aliens...
No, seriously people, I'm not saying that life on Earth was brought here by aliens. 
What I'm saying is that panspermia is one potential explanation for why the trends of genetic complexity that we see suggest that life on Earth could be older than the planet itself. 

Now, this theory doesn't explain where those components came from in the first place and it doesn't mean that life is necessarily abundant in the universe. 
'Cause the seed still needs to find fertile soil in order to sprout, right? 
So it could still be that life we have here on Earth is rare, maybe even unique within our larger celestial neighborhood. 

What these new studies suggest is just that the best question may not be 'Are we alone in the universe?', it may be more like 'Are we the first advanced life in the universe or are we just the most recent link in a chain of life that dates back to the early universe'.

Thanks for joining me for this especially heady episode of Sci Show Space. If you would like to learn how you can help us keep exploring the universe together, go to and don't forget to go to and subscribe.