In the beginning there was nothing, and then after a long while we had the earth, but without
any people.
In fact, it took quite a bit of time before anything living and breathing at all showed
up.
But eventually they did, which is a good thing, because otherwise there’d be no one to watch
this video, or make this video, or… well you get the idea.
But sometimes you might ask, where did people come from?
You wouldn’t be the first to ask and people have literally died defending their theory
of why we exist, but in modern times should be thankful scientists haven’t started wars
or gone out on murderous crusades in defense of their existence and evolution theories.
Most rational people these days agree that species have evolved over a very long period
of time, but that doesn’t really explain why we or any other living thing exists at
all.
Today we’ll have a crack at trying to solve the riddle of existence.
First we should say that the question of how life began and evolved on Earth is not an
exact science.
For the most part scientists use something called the fossil record to see when certain
events occurred, but the problem with that is there are still a lot of missing bits.
Scientists can see certain events, but then there are long periods where it seems like
nothing happened, or they haven’t found anything to fill the gaps.
The experts can also use something called the molecular clock, which in simple terms
means scientists look at the story written in the DNA of living organisms.
By doing that they can compare how similar or different species are on a molecular level
to try and figure out when different species diverged, or split off each other.
As we said, in the beginning there wasn’t any life.
Some people might tell you that God made man and other living species out of the dust of
the Earth, doing a fine job but making a few mistakes here and there, or perhaps purposely
making everything with some design flaws.
While God having a man factory in the sky was a popular theory for a long time, it’s
a hard sell to most people these days.
The theory of evolution gradually supplanted biblical stories of a Garden of Eden with
one recent survey by Pew Research Center stating that 81% of Americans believe that humans
evolved over time.
So, let’s stick with the theory of evolution.
How does that go?
It’s a rather long story.
In fact, it’s the longest story ever told, so we’ll try to shorten it for you.
It’s generally thought life on earth got off the ground about 3.8 billion years ago,
but as we said, this is only a ballpark figure - an informed guess.
That first life might have evolved in something called alkaline hydrothermal vents under the
sea.
Many scientists say that these vents were the ideal setting for the production of something
called Ribonucleic acid, or, RNA.
This is important stuff, so we’ll give you the dictionary definition of this rather than
try to paraphrase.
That definition reads, “A nucleic acid present in all living cells.
Its principal role is to act as a messenger carrying instructions from DNA for controlling
the synthesis of proteins, although in some viruses RNA rather than DNA carries the genetic
information.”
The theory goes that these hydrothermal fluids went up through vents and hit the primordial
seawater.
In short, the reaction from this ended up producing simple organic molecules, and a
bunch of reactions led to the formation of amino acids.
Let’s just say you have bubbles in the water full of these molecules and these are self-replicating.
This led to the production of the first cells, or protocells.
We then got the production of bacteria and archaea, which scientists will tell you are
like the roots of the tree of life.
Other theories do exist as well, such as life coming by way of a rock from Mars.
That would make us part-Martian.
Or were these reactions caused under the ice, or from an electrical storm?
No one knows for certain.
What we do know is that single cell organisms were eventually produced.
Life did not start out looking at all like a finished product.
Humans and turtles and starfish all had to evolve from single cell organisms.
The oldest of those according to the fossil record lived about 3.5 billion years ago and
that’s all there was for a long time, about a billion years in fact, with single cells
doing nothing but simply existing.
Then about 2.4 billion years ago something special happened, what scientists call the
“great oxidation event” where more oxygen started appearing on Earth due to a number
of factors.
Then 2.3 billion years ago the Earth got very cold, possibly because there wasn’t much
volcanic activity.
It might have also been because high concentrations of O2 caused the methane (CH4) in the atmosphere
to oxidize to form CO2.
This led to what is now called the first “snowball Earth.”
It didn’t stay a giant ball of ice for long and when the ice melted more oxygen was produced.
About 2.15 billion years ago there is evidence of photosynthesis occurring on Earth.
More oxygen was produced as a result of this.
Around two billion years ago there is evidence of a big event when one single cell got with
another single cell.
Together they got along, and they reproduced together, forming something called Eukaryotic
cells.
Now things are really taking off, because soon they led to the formation of the first
green plants and green algae.
But it was around 900 million years ago when an even greater event happened, the formation
of true multicellular life, and eventually entities known as Placozoa.
These three-celled creatures are tiny, only about 1 mm across, but they are the ancestor
of all animals on Earth.
You must remember that these things were not exactly complex animals.
Humans have over 37 trillion cells, while the mighty placozoa has just three.
It took us awhile just to get to the point where three celled organisms were swimming
in Earth’s oceans, and that’s with many, many parts left out.
Sorry evolutionary scientists, but we don’t have nine hundred million years to tell this
story.
To cut the story shorter again, the Earth froze into a giant snowball another time.
It thawed out, and more complex organisms evolved that lived in the water, some of which
were the ancestors of the modern jellyfish we all know and love.
Then around 630 million years ago something great happened again, and that was living
things appearing with bilateral symmetry.
What’s that you might inquire?
Well, these are animals that have a defined top and bottom part.
Before that things mostly looked like a piece of floating jelly.
The first of these new exciting, and more aesthetically pleasing creatures may have
been “Vernanimalcula guizhouena”, a bit of a mouthful and honestly still not much
to look at.
It’s resembles a circular-shaped spring, and has even been nicknamed the “small spring
animal”, but we prefer to call it the “Pretzel Worm.”
Now animal life is really out to the races, but we are still a long way from things like
you that can peel oranges and talk about existential philosophy.
It started happening though when the Pretzel Worm evolved, or we should say kind of split
off into two different forms, which we call protostomes and deuterostomes.
The former will become the arthropods, i.e. things with an exoskeleton, such as insects
and spiders.
The latter will become the vertebrates, such as mammals, birds and fish.
Around 550 million years ago the sea was full of these more complex animals and we know
from fossils that in those waters were early starfish, jellyfish and sea anemones.
But soon some things started growing a backbone, and we don’t mean they were getting braver.
One of the first vertebrates we got was something that resembled a tadpole.
Starting around 565 million years ago some of these things didn’t just float about,
but they moved of their own accord.
They were going places.
It would just take a few more million years to get much farther.
And just for a second, try and grasp what’s happened in the last ten years, or 100 years,
and then try and grasp a million and realize how short our time as modern people has actually
been when compared to the ages our tadpole ancestors spent swimming around the ocean.
Then about 535 million years ago something major happened again, something scientists
know about by looking at fossils and seeing an explosion of life forms.
They call this the Cambrian explosion, and no one knows really why so many complex animals
suddenly appeared.
That’s a story in itself and scientists are still debating what caused it.
The explosion didn’t exactly happen overnight, with the University of Berkley saying it was
more like over 13 million years, so okay, not an explosion in the way we normally think
about it but on a geological scale that’s just a blink of the eye.
During that time things that looked a lot like small animals we see today started popping
up.
Some of the earliest vertebrates looked a bit like modern eels, and one of the most
famous pictures of a fossil is something that looks like a giant woodlice, which is in actuality
an arthropod called a Trilobite.
But we will have to fast forward again.
Around 490 million years ago we had the “Great Ordovician Biodiversification Event,” a
mouthful of a name that means more diversity in animal groups and plants.
Give it a few more million years and plants would start to colonize the land.
In the sea, the fish are splitting into two groups, the boney ones and the ones called
cartilaginous fish who will one day turn into sharks.
Then around 417 million years ago we have another hugely important event, when something
called the lungfish appeared.
They had a set of lungs that allowed them to breathe out of water, unlike other fish.
If their water source dried up, they could survive, a huge evolutionary advantage.
397 million years ago we finally get the first tetrapod, or four legged animal, a momentous
event because these four-legged things would end up taking over the land.
They would become all mammals, birds, amphibians and reptiles.
So, about this time we had things that could breathe out of water and animals whose fins
were developing into limbs.
But let’s just say that over 300 million years ago, during that era, these life forms
split and started to look different.
Some for example would become the reptiles, dinosaurs, while others would become birds.
We also had the synapsids, the first mammal-like reptile.
But building things is never easy and there are always periods of collapse.
There was a mass extinction around 250 million years ago.
Some things survived, and the dinosaurs would take over after this.
Over the next hundred million years we had lots of dinosaurs, evolving mammals, the first
proper birds, and then there is a hazy period, for scientists anyway, because no one knows
exactly how it happened but about 100 million years ago the mammals split into lots of different
groups.
They would become all the primates, rodents, elephants, armadillos, bats, pooches, pretty
much the whole shebang.
You have this explosion and split, all the while dinosaurs are wandering the Earth, the
biggest ever dinosaurs in fact, including the giant sauropod.
Many millions of years later on land grass starts growing and that’s a huge deal, but
around five million years after things started getting green there was another mass extinction,
and this is called the Cretaceous-Tertiary extinction.
Goodbye giant dinosaurs, goodbye plesiosaurs, nice to have met you pterosaurs, rest in peace
dear ichthyosaurs.
But dry your tears, because now we take over.
The age of the mammals beckons.
The primates split into two groups, and one of those groups will become monkeys and apes
and eventually us.
Then around 55 million years ago the Earth heats up and we have another extinction.
Lots of life dies, but lots survives, too.
The fossil record over the next few million years shows things that looked like whales
and dolphins, but we also got Ida.
That’s the fossil that could be the missing link, the magic monkey, Darwinius masillae,
a primate that somewhat resembles homo sapiens.
And over millions more years we would see more primates.
They would split, such as when apes branched off from Old World monkeys about 25 million
years ago.
Over millions of years other primates would emerge, such as gibbons, orangutans, and gorillas.
Then about 6 million years ago relatives of us humans would diverge from chimpanzees and
bonobos.
We got the Homo genus around 2.5 million years ago.
These look like ape people, but then they stood up straight, we call these folks Homo
Erectus.
We later got the more intelligent Neanderthals, hunting and gathering, but we don’t think
they had painting and abstract thinking.
After this was the rise of homo sapiens.
We had the Great Leap Forward perhaps 50,000 years ago, when humans started drawing on
cave walls and wearing jewelry, thinking about the future, planning, and that led to agriculture,
society, language, art, politics, and finally you watching this on a digital platform and
wondering why it all started in the first place.
Why molecules reacted and formed a cell?
Why those cells got it on?
Why things came together and diverged.
And the simple reason might be, that it just happened.
In the beginning there was a reaction, and that led to another reaction, and that’s
why we exist.
Or do you disagree?
Tell us in the comments.
Also, be sure to check out our other video What Happens When You Die?
Thanks for watching, and as always don’t forget to like, share and subscribe.
See you next time.