By now, youâve 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. Iâm 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 youâre watching me in California
right now, then about 500 million years ago, the place that you currently think of as âhereâ
was actually on the equator ⌠and it was underwater. Likewise, if youâre in the UK, then your
âhereâ was almost at the South Pole. And your next door neighbor was Africa. We know all of this thanks to paleogeography,
the study of how the physical face of Earth has transformed over time. And itâs this movement of the continents
that has driven many of the ma jor revolutions in lifeâs history -- its advances and its
setbacks, its explosions of life and its extinction events. So, if natural history is the study of how
we got here, then you also have to understand how here got here. If you wanna know how your âhereâ 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 didnât 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. Wegener was the first to propose the idea
of continental drift -- and the notion was so outlandish at the time that it basically
cost him his career. And part of why no one accepted Wegenerâs
theory was that no one in his day had ever seen the bottom of the ocean. Until the mid-20th century, most scientists
assumed that the seafloor was 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 was an enormous
mountain range running through the middle of the Atlantic. Eventually, more of these undersea mountain
ranges, called mid-ocean ridges, were found in all the worldâs oceans, and they all
were volcanically active. These ridges, it turned out, are where the
seafloor is made. Geologists realized that these mid-ocean volcanoes
are actively creating the rocky material of the seafloor and spreading it outward, in
a process called seafloor spreading. But what the sea 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 landmasses, known
as the continental crust, just a few centimeters at a time. And as the oceanic crust sinks back into Earthâs
interior, it begins to melt and mix with the mantle. So, seafloor spreading and subduction are
the two primary mechanisms behind plate tectonics -- the theory of how giant chunks of Earthâs
crust, called plates, move around the surface. And together, they explain what Alfred Wegener
never could -- they show us HOW the continents of our planet come together and break apart. But Wegener was right -- throughout the planetâs
history, land masses have been joining together to form supercontinents, only to break up
again millions of years later. Supercontinents begin to separate when the
mantle thatâs churning around beneath them starts to 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, they 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 -- thatâs actually how the Atlantic Ocean formed. This whole process of continents coming together
and splitting apart is known as the supercontinent cycle, and IT is what has changed the face
of Earth over the eons. Now, youâve probably heard of Pangaea, the
landmass that contained almost all of Earthâs dry land about a quarter billion years ago. For a long time, experts thought it was the
worldâs first supercontinent. But today we know it wasnât the first. And it wonât be the last! One of the earliest supercontinents that scientists
have evidence for is called Kenorland. It existed 2.7 to 2.5 billion years ago, toward
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 call it a supercontinent,
Kenorland actually wasnât much bigger than Australia is today. Life on Earth at the time of Kenorland was
probably mostly single-celled, like the photosynthetic cyanobacteria that were starting to add oxygen
to the atmosphere. Then, 700 million years after Kenorland spread
apart, another supercontinent began to form called Nuna, or Columbia depending 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 itâs here where we find fossils of the
earliest plant-like organisms, red algae, which lived in a shallow sea in whatâs now
India. Nuna broke apart, but the fragments came back
together about 100 million years later. This new continent, called Rodinia, was the
first supercontinent that geologists found had existed before Pangaea. And geologists were able to reconstruct Rodinia
after they noticed that Labrador on Canadaâs east coast fit quite nicely into the west
coast of South America. Rodinia 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 Pannotia, came together. And here the first animals are 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 mark the Cambrian Explosion. Animals probably didnât live on Pannotia,
though, because no fossils have been found in terrestrial rocks from that time. But the land wasnât lifeless -- it had likely
been colonized by pioneering bacteria, algae, and then, the fungi! After Pannotia broke up, about 550 million
years ago, the continents began looking more like the world we recognize. 470 million years ago, in the Ordovician Period,
the first plants began 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 itâs known by the catchy portmanteau Euramerica,
because it contained parts of both North America and Europe. Euramerica 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 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, Pangaea. 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 wasnât exactly a picnic. Because Pangea was so incredibly huge, moisture
from the oceans couldnât reach the interior, which made most inland regions pretty much uninhabitable. And of course, making things even less picnicky
were ... two really terrible mass extinctions. First was the 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 Pangea in whatâs now Siberia. These eruptions likely set coalfields 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. Fifty million years later, the 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 spinosaurids, for example,
lived on the remnants of Gondwana. Meanwhile, horned dinosaurs like Triceratops
almost all lived in North America. Then, after the K-Pg Extinction wiped out
the non-avian dinosaurs 66 million years ago, it was mammalsâ 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 5 to 10 million years, allowing annimals to cross newly formed
land bridges into new environments ones we can recognize pretty well today. But of course, things keep moving today, just
like they always have -- at a rate of about 2.5 centimeters a year in fact And, scientists can predict how the world
might look in, say, 50 million years, based on how fast the continents are moving, and
in which direction. So, what will future Earth look like? Well, North and South America are moving west,
as the Atlantic Ocean continues to grow. Africa is moving north and will collide with
Europe, probably forming a huge mountainous plateau, kind of like the Himalayas, where
the Mediterranean Sea is now. Australiaâs 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 supercontinent like Pangaea in 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 Novopangaea, envisions
a future Earth thatâs 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 descendents and the other descendants of the modern world, will have
evolved and diversified to occupy a planet that looks totally different. But theyâll be along for the same ride that
weâre on today, as forces deep within the Earth cause our idea of âhereâ to slowly
drift, just as it has for billions of years. You and I have been through a lot together
today, so I appreciate you sticking around for this whole saga of the supercontinents. As always, I want to know what you want to
learn, about the story of life on Earth, so leave us a comment down below. And if you havenât already, go to youtube.com/eons
and subscribe. And, if youâre like me and I hope you are and youâre interested
in the big picture things, then you should really watch Space Time, a show that answers
terrifyingly difficult questions, like how big the universe is and whatâs up with dark
energy. Trust me, your brain WILL thank you.
They will always challenge the data. How do they know? Well because of this and that other thing. Well, how do they know that? And at some point they'll say that the data is unprovable and so therefore invalid. It always amazes me how strict they are about proof with everything except for the Bible. That's just unassailable.
Fun and interesting video, but religious friend didn't seem to think so.
Send him these:
Evidence (19 minutes) It's a great video about epistemology.
And this 3-parter There Are No Gods (7 mins, 14 mins, 19 mins)
Your best bet is to show him arguments that poke holes in religions other than his own. Those are better able to get past his blinders.
I was going to ask why you cared about changing their perception of our reality. Then I remembered how I am always challenged by my family. They will talk in circles for hours, if I give into it. They just want to bring me to their level of "I need you to believe what I believe!" No thank you. I don't want to be an agnostic/atheist with christian tendencies. I don't want to break your faith and have you completely agree with me. That means nothing . I just want you to understand the world from another view, and not desire to enforce your beliefs on others - Like that sharia law they are so concerned about.