B2 High-Intermediate 1 Folder Collection
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You just clicked on this video, so you're alive
and interestingly in order to understand exactly where you came from
we must first understand what it means
to be alive. Life is an organised
genetic unit capable of metabolism,
reproduction and evolution. It's important to
remember this as we go way back in history to figure out exactly how you got here.
Astronomers believe our solar system began
to form 4.6 billion years ago, when a star exploded
and then collapsed to form the sun
and around 500 smaller planets collided with each other
to from the inner planets we know today, including your home, Earth.
For about 600 million years
Earth was too hot for life, most of the water was
evaporating into space, and even if some simple chemical
reactions began to take place creating life,
the comets and meteorites hitting Earth at the time
would have brought enough heat to make the developing oceans boil,
destroying all potential life. As comets and meteorites subsided
Earth cooled and it became possible for water to remain on the surface.
And so, life begins
about 3.7 billion years ago. There are many theories about how
exactly it began, some believe simple life
arrived from a meteorite, while others think chemical evolution
started with compounds reacting to heat,
or perhaps they were struck by lightning. And while the exact date
is difficult to pinpoint, a new study claims to have found
the oldest fossil ever at 3.77 billion
years old. An ancient microbe that flourished
around a hydro-thermal vent on the ocean floor. It's around
this time that the first simple cells began to evolve
on Earth, they were able to capture energy, replicate themselves
and evolve and became the single unit
on which all life will be built, including you.
For 2 billion years, all organisms on Earth are
unicellular, and they likely lived in the oceans,
shielded from the hard ultraviolet (UV) light of the sun
but then something remarkable happened...
Photosynthesis.
Around 2.5 billion years ago, a random mutation occurred that was
advantageous to cells, and they began using the energy of the sun to power their metabolism.
And since oxygen, or O₂,
is the product of photosynthesis, our atmosphere changed
eventually creating the ozone layer which acted to shield the Earth
from the sun's deadly light. Of course at this point
O₂ is poisonous to most organisms
but over time, cells evolve to tolerate it, and because metabolic
reactions using O₂ were more efficient, cells could grow larger.
Around 1 billion years later,
cells begin to engulf and co-opt smaller cells,
increasing their abilities to live in diverse environments. This
selective advantage led to cells sticking together in a coordinated manner
even after dividing, and these cells eventually
began exchanging genetic material,
AKA, they had sex. Single celled organisms would divide by mitosis
or simple nuclear division, but once
meiosis evolved, genetic reorganisation began to occur
and the rate of evolution increased as offspring
were now more genetically variable and some of these offspring
were more likely to survive and reproduce, and so the tree of life
began to explode. First there were plants
and then fungi, coral then protosomes like crabs,
echinoderms like sea urchins and then fish like sharks
and cod, and tetropods evolved from fish
and began adapting to living outside of the water part-time,
initially gulping air and absorbing oxygen in the gut.
As time passes, species would evolve lungs separate
from the gut for absorbing air as well as a new way to walk
on land. In come amphibians, reptiles,
dinosaurs and finally, mammals. In fact our entire
ancestry stems from a cute, furry tailed, rat-like mammal
which survived and thrived around 66 million years ago
just after an asteroid wiped out the dinosaurs.
And after tens of millions of years of evolution
and new species emerging, one branch of the Protungulatum family tree
evolved into our ape and monkey ancestors. And nearly 4 millions years ago, one of the first
human-like creatures arrive, Australopithecus Afarensus,
the most famous discovered remains being that of Lucy, who stood upright.
100,000 generations later
or 2-3 millions years ago, the species group
'homo' began which had a bigger brain
and started using their hands for more complex activities like creating and
wealding tools. This was the first step of transforming
our environment to improve our lives. It was also
a catalyst to switching from a vegetarian diet
to one containing meat which is a more concentrated
form of nutrition, and less effected by seasonal shortages.
These simple stone tools allowed us to rip through meat
and would become the tool of choice for 2 million
years. And around 1.8 million years ago, homo erectus
emerged, the direct ancestor to our species.
Finally, a few hundred thousand years ago, modern humans,
or homo sapiens, step into the light. Larger,
smarter and more capable than their predecessors.
Interestingly, we almost didn't make it.
A climate change event around 140 thousand years ago
plummeted the human population to only hundreds of people,
an endangered species. But, we survived.
As recently as 60,000 years ago
three different species of the 'homo' family co-exist.
Homo neanderthalensis, homo denisova and we,
homo sapiens, which all lived on this planet together.
In fact, sapiens and neanderthalensis mated quite often which is why
most contemporary humans, including you
have neanderthalensis DNA. The neanderthalensis died out around
30,000 years ago when homo sapiens were arriving
in what is now Europe, and from this point on, the
homo sapiens were the only living humans left on Earth.
Unlike our primate relatives whose evolution favored strength,
ours chose brain power, in fact
your brain weighs 2% of your body weight
but uses 20% of your caloric intake. And this brain power
allowed us to survive in a variety of environments, as we began to
migrate around the entire world. Where we started
as small wandering groups of less than 100
we began to settle in groups of thousands and millions
and now, billions. You were born
a homo sapien, and that is how you got here.
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How Did You Get Here?

1 Folder Collection
林宜悉 published on April 4, 2020
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