I'm Fraser Cain, the publisher of Universe Today.
No answers today, only a question.
But it's one of the most interesting and meaningful questions we can possibly ask.
Where does life come from?
How did we get from no life on Earth, to the rich abundance we see today?
Charles Darwin first published our modern theories of evolution- that all life on Earth
is related; adapting and changing over time.
Look at any two creatures on Earth and you can trace them back to a common ancestor.
Humans and chimpanzees share a common ancestor from at least 7 million years ago.
Trace back far enough, and you're related to the first mammal who lived 220 million
years ago.
In fact, you and bacteria can trace a family member who lived billions of years ago.
Keep going back, and you reach the oldest evidence of life on Earth, about 3.9 billion
years ago.
But that's as far as evolution can take us.
The Earth has been around for 4.5 billion years, and those early years were completely
hostile to life.
The early atmosphere was toxic, and a constant asteroid bombardment churned the landscape
into a worldwide ocean of molten rock.
As soon as the environment settled down to be relatively habitable, life appeared.
Just half a billion years beyond the formation of the Earth.
So how did life make the jump from raw chemicals to the evolutionary process we see today?
The term for this mystery is abiogenesis and scientists are working on several theories
to explain it.
One of the first clues is amino acids, the building blocks of life.
In 1953, Stanley Miller and Harold Urey demonstrated that amino acids could form naturally in the
environment of the early Earth.
They replicated the atmosphere and chemicals present, and then used electric sparks to
simulate lightning strikes.
Amazingly, they found a variety of amino acids in the resulting primordial soup.
Other scientists replicated the experiment, even changing the atmospheric conditions to
match other models of the early Earth.
Instead of water, methane, ammonia and hydrogen, they wondered what would happen if the atmosphere
contained hydrogen sulfide and sulfur dioxide from volcanic eruptions.
Environments around volcanic vents at the bottom of the ocean might have been the perfect
places to get life started, introducing heavier metals like iron and zinc.
Perhaps ultraviolet rays from the younger, more volatile Sun, or abundant radiation from
natural uranium deposits played a role in pushing life forward into an evolutionary
process.
What if life didn't start on Earth at all?
What if the building blocks came from space, drifting through the cosmos for millions of
years.
Astronomers have discovered amino acids in comets, and even alcohol floating in distant
clouds of gas and dust
Maybe it wasn't the organic chemicals that came first, but the process of self organization.
There are examples of inorganic chemicals and metals that can organize themselves under
the right conditions.
The process of metabolism came first, and then organic chemicals adopted this process.
It's even possible that life formed multiple times on Earth in different eras.
Although all life as we know it is related, there could be a shadow ecosystem of microbial
life forms in our soil or oceans which is completely alien to us.
So how did life get here?
We just don't know.
Maybe we'll discover life on other worlds and that will give us a clue, or maybe scientists
will create an experiment that finally replicates the jump from non-life to life.
We may never discover the answer.
Thanks
for watching.