[Music]
by now you're surely picked up on the
idea that the study of natural history
is basically the study of how the world
has changed the study of how we all got
here and of course the world continues
to change all the time
I mean literally I'm not just talking
about how life adapts or how the climate
is changing I mean the planet itself as
an object is in a constant state of flux
because the ground beneath your feet is
always moving so the place where you are
right now was not always there for
example if you're watching me in
California right now then about 500
million years ago the place that you
currently think of as here was actually
on the equator and it was under water
likewise if you're in the UK then you're
here was almost at the South Pole in
your next-door neighbor was Africa we
know all this thanks to paleo geography
the study of how the physical face of
Earth has transformed over time and it's
this movement of the continents has
driven many of the major revolutions in
life's history its advances in its
setbacks its explosions of life and its
extinction events so if natural history
is the study of how we got here and you
also have to understand how here got
here
if you want to know how you're here got
to be where it is you first have to know
where land comes from and how it behaves
and for a long time we just didn't know
the idea that the continents could
actually move was first proposed in 1912
by German scientist Alfred Wegener he
spent years traveling the world
collecting geological and fossil
evidence to argue that all of the
continents were once connected begginer
was the first to propose the idea of
continental drift and the notion was
sell outlandish at the time that it
basically cost him his career and part
of why no one accepted begginers theory
was that no one in his day had ever seen
the bottom of the ocean until the mid
20th century most scientists assume that
the seafloor is basically featureless
like a giant wading pool but in the
1950s and 60s pioneering researchers
like Marie Tharp and Bruce heezen began
studying the bottom of the ocean and
they found that there is an enormous
mountain range running right through the
middle of the Atlantic
eventually more of these undersea
mountain ranges called mid-ocean ridges
were found in all the world's oceans and
they were all volcanically active these
ridges it turned out or where the
seafloor is made geologists realized
that these mid-ocean volcanoes are
actively creating the rocky material of
the seafloor and spreading a network in
a process called seafloor spreading but
what this he gives it also takes away
far from these ridges at the edges of
continents researchers also found huge
trenches and here the dense rocks of the
seafloor dive below the lighter rocks of
the continents in a process called
subduction so the denser heavier crust
that makes up the seafloor known as the
oceanic crust moves under the lighter
land masses known as the continental
crust just a few centimeters at a time
and as oceanic crust sinks back into
Earth's interior begins to melt and mix
with the mantle
so seafloor spreading and subduction are
the two key mechanisms behind plate
tectonics the theory of how giant chunks
of Earth's crust called plates move
around the surface and together they
explain what Alfred Wegener never could
they show us how the continents of a
planet come together and break apart but
Victor was right
throughout the planets history land
masses have been joining together to
form supercontinents only to break up
again millions of years later super
continents begin to separate when the
mantle that's turning around beneath
them stressed a change like in direction
or temperature or intensity these kinds
of changes we think can cause plates
that were once pushed together to
gradually spread apart when plates
separate they first create a Rift Valley
like the Great Rift Valley in Africa
then as they keep spreading apart that
can form narrow seas which is how the
Red Sea came to be eventually these gaps
can open up to become a whole new ocean
that's actually how the Atlantic Ocean
formed this whole process of continents
coming together and splitting apart is
known as the supercontinent
and it is what has changed the face of
the earth over the eons now you've
probably heard of Pangaea the landmass
that contained almost all of Earth's dry
land about a quarter billion years ago
for a long time experts thought that was
the world's first supercontinent but
today we know it wasn't the first and it
won't be the last one of the earliest
super continents that scientists have
evidence for is called Kannur 'land it
existed 2.7 to 2.5 billion years ago for
the very end of the Archaean Eon it was
made of continental crust that would
eventually become parts of North America
and Africa and even though we called the
supercontinent Canole and actually was
much bigger than Australia's today life
on earth at the time of Konoe Rowland
was probably mostly single-celled like
the photosynthetic cyanobacteria that
were starting to add oxygen to the
atmosphere then 700 million years after
Crenn Orland spread apart another
supercontinent began to form called nuna
or Columbia depending on who you ask
the northern reaches of nuna included
land that would eventually become North
America and Antarctica and in the South
were the cores of South America and
Africa nuna existed from 1.8 to 1.4
billion years ago in the middle of the
proterozoic eon and it's here where we
find fossils of the earliest plant-like
organisms red algae which lived in a
shallow sea in what's now india nuna
broke apart but the fragments came back
together about a hundred million years
later this new continent called Rodinia
was the first supercontinent that
geologists had found existed before
Pangaea and geologists were able to
reconstruct Lavinia after they noticed
that Labrador and Canada's East Coast
fit quite nicely into the west coast of
South America Virginia broke apart about
900 million years ago and shortly after
that the world was plunged into another
long Ice Age about 650 million years ago
the next supercontinent called panocha
came together and here the first animals
were found in the fossil record living
in coastal waters from the poles to the
equator
first came the mysterious Ediacaran
fauna and then the animals that marked
the Cambrian explosion animals probably
didn't live on panocha though because no
fossils have been found in terrestrial
rocks from that time but the land wasn't
lifeless it had likely been colonized by
pioneering bacteria algae and then the
fungi after for no sure broke up about
550 million years ago the continents
began looking more like the world we
recognized 470 million years ago in the
Ordovician period the first plants begin
to live on land
the earliest plant fossils have been
found in South America which was part of
the continent of Gondwana
then 420 million years ago in the late
silurian the first millipedes crawled
through the undergrowth on a separate
continent just north of Gondwana and
it's known by the catchy portmanteau
year
shaaka because it contained parts of
both North America and Europe your
America is also where the earliest
fossils of insects have been found about
20 million years later then toward the
end of the Devonian period 365 million
years ago the first amphibians left the
swamps to explore the ancient forests
that would later form the coal deposits
of Europe and North America and then the
earliest amniotes vertebrates that lay
shelled eggs on land showed up 310
million years ago right before the
formation of the most famous and most
recent supercontinent Pangea Pangaea
began to form 300 million years ago at
the end of the Carboniferous when North
America and Eurasia together known as
Laurasia collided with Gondwana and
because there were no oceans in their
way animals were free to roam all over
Pangaea which is why similar species are
found in areas all over the world in
this time but life there wasn't exactly
a picnic because Pangaea was so
incredibly huge moisture from the oceans
couldn't reach the interior which made
most inland regions pretty much
uninhabitable and of course making
things even less picnicky were too
really terrible mass extinctions first
was a Permian Triassic extinction 252
million years ago aka the Great dying it
was probably caused by a series of
massive volcanic eruptions from fissures
in Pangaea in what's now Siberia these
eruptions likely set coal fields on fire
and dumped massive amounts of co2 into
the atmosphere and oceans the super hot
air and super acidic rain and seas that
followed killed almost everything 50
million years later that Triassic came
to a close with another mass extinction
wiping out a huge number of crocodile
and mammal relatives this too seems to
have been caused by volcanic activity
only this time as North America started
to break away from the rest of Pangaea
but among the survivors were the
dinosaurs and as Pangaea broke apart
dinosaurs on different continents became
isolated and developed into vastly
different forms the semi-aquatic
Spinosaurus for example lived on the
remnants of Gondwana meanwhile horned
dinosaurs like Triceratops mostly lived
in North America
then after the KPG extinction wiped out
the non-avian dinosaurs 66 million years
ago it was mammals turn living on
isolated continents like the dinosaurs
once did they too diversified into lots
of different and weird forms finally
those isolated continents came into
contact again in the last five to ten
million years allowing animals to cross
new land bridges into new environments
ones we can recognize pretty well today
but of course things keep moving today
just like they always have had a rate of
about two and a half centimeters a year
in fact and scientists can predict how
the world might look and save 50 million
years based on how fast a cotton
are moving and in which direction so
what will future earth look like well
North and South America are both moving
west as the Atlantic Ocean continues to
grow Africa is moving north and will
collide with Europe probably farming a
huge mountainous plateau kind of like
the Himalayas where the Mediterranean
Sea is now Australia is also moving
north and will eventually smash into the
Indonesian archipelago
but beyond the next 50 million years or
so the future becomes harder for us to
see one theory called Pangaea Ultima
proposes that a subduction zone will
form off the east coast of the Americas
closing off the Atlantic and forming
another super continent like Pangaea and
about 250 million years another theory
called Amasia supposes that the Atlantic
will keep getting bigger and that North
America will join Europe and Asia at the
North Pole and a third theory called
Nova Pangaea and visions of future earth
that's similar to Amasia but with the
Pacific Ocean closed off as Australia
and Antarctica move into the former
Ocean basin by then of course a quarter
billion years from now our descendants
and the other descendants of the modern
world will have evolved and diversified
to occupy a planet that looks totally
different but they'll be along for the
same ride that we're on today as forces
deep within the earth cause our idea of
here to slowly drift just as it has for
billions of years
yuuna have been through a lot together
today so appreciate you sticking around
for this whole saga the supercontinents
as always i want to know what you would
have learned about the story of life on
earth so leave us a comment down below
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