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.
Because my dad's pullout game was weak...