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The Phanerozoic eon - Contenido educativo
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Se describe brevemente, en inglés, el eón Fanerozoico con sus tres eras.
Hello! This is the video about the Phanerozoic Eon, which, as you already know, started 545 million years ago
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and is still the Eon in which we live.
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Then, as I explained in class, rocks from times before this Eon, before the Phanerozoic Eon,
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not show fossils of any animals from the types of animals okay that exist currently okay and
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i remind you that in the taxonomy in the classification of living things phyla are
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the different basic types of whatever kingdom of living things we are speaking about if we
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are speaking about animals the phyla are the basic types of animals okay and the singular of phyla is
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a phylum so before this time before 545 million years ago there were living things on the planet
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but there were no animals like the animals that exist now except perhaps some sponges and a
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jellyfish that existed around 600 to 550 to 550 million years ago okay so apart from sponges and
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jellyfish there were no animals like the ones that exist now then as i explained in class
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almost all the different types of animals that exist now and this means almost all the different
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animal phyla appeared in a short time short time means hundreds of thousands of years okay in a
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few hundreds of thousands of years almost all the different animal phyla appeared hundreds of
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thousands of years for a person is a lot but from the point of view of geology it is almost nothing
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so it is a sudden appearance in a very short time short from the point of view of geology
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almost all different types of animals appeared of course when i say types of animals i do not mean
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different the well the species that exist now okay what i mean is that for every basic type of animal
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represent different representatives different species that do not exist now ancient species
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that represent the basic types of animals appeared at this time, at 545 million years ago.
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Then this marks the beginning of the Cambrian period.
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The Cambrian period is the first period of the Paleozoic era, which is the first era of the Phanerozoic eon.
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Then since this sudden appearance of life, this explosion of life, happened at the beginning of the Cambrian period, this is called the Cambrian explosion.
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And I explain this in class.
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Then everything that we have studied that happened on Earth before this time, before 545 million years ago, is called the Precambrian.
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So precambrian is everything that happened before, the Cambrian explosion, which is the explosion of life of different types of animals that existed and that still exist now.
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Then the Phanerozoic is divided into three eras, and the three eras are called the Paleozoic, the Mesozoic and the Cenozoic eras, each of which is divided into periods.
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So the first era, the Paleozoic era, started with the Cambrian explosion 545 million years ago and finished 250 million years ago.
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The trilobites are the typical fossils of the Paleozoic era.
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So these animals lived in the ocean and they were arthropods, so animals with jointed legs and exoskeleton.
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There are no trilobites now, but the fact is that these representatives of the arthropods appeared 545 million years ago.
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So the phylum arthropods appeared 545 million years ago.
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The arthropods that existed at that time are different from the arthropods that exist now, but they were arthropods.
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So the different phyla appeared 545 million years ago, even though the species that existed then are different from the species that exist now.
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Then trilobites are one example of arthropods. There were other arthropods at this time, like eurypterids, so these kind of scorpions from that time.
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But not only animals, ok, also different plants appeared, and what is very important is that terrestrial plants appeared during the Paleozoic era.
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Most of the plants during the Paleozoic era were plants that depended on water to reproduce, the same as mosses and ferns do now.
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We studied this in the first test, so that most sun ferns can only reproduce if there is liquid water for their sperm cells to swim.
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But near the end of the Paleozoic era, then different plants appeared, plants that reproduce with pollen and seeds.
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So the plants that reproduce with pollen and seeds do not need water, because they do not need sperm cells to swim in water.
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they reproduce with pollen and seeds and it means that they may reproduce even if there are dry
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conditions. So the plants that reproduce with pollen and seeds appeared near the end of the
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Paleozoic era. Then vertebrates are animals that belong to a phylum, the phylum Chordates. Then
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the phylum chordates appeared also in the cambrian explosion 545 million years ago
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the first chordates were not vertebrates but bit by bit the first chordates evolved into vertebrates
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and the first vertebrates that appeared were fish and as we studied in first so most fish evolved
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into other fish that evolved into other fish etc but some fish evolved into amphibians most
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Most amphibians evolved into amphibians that evolved into other amphibians, but some amphibians evolved into reptiles.
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In the Paleozoic era, the only vertebrates that existed were first fish, then later also amphibians, and later also reptiles.
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Here you have images of fossils of the trilobite and the eurypterid, and these are plant fossils.
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These are ferns from the Paleozoic era.
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Then near the end of the Paleozoic era, Pangea formed.
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So the continents merged forming Pangea near the end of the Paleozoic era.
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And also the last period of the Paleozoic is called the Pyramian, and at the end of
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the Permian, there was the worst, the greatest, massive extinction known, okay?
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So at the end of the Paleozoic era, at the end of the last period in the Paleozoic era,
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the Permian, an enormous number of animal and plant species got extinct, and this includes
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the last trilobites, okay?
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So the last trilobites died at the end of the Paleozoic.
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Why did this extinction?
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happen? We don't know. We don't know the reasons for this massive extinction, the
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worst massive extinction that we know of. The fact is that there is a big
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difference in the fossil record, a very big difference between the end of the
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Permian, this means the end of the Paleozoic era, and the beginning of the
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next period. The next period is called the Triassic and the Triassic is the
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first period of the Mesozoic era. So this extinction event was so
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terrible that scientists consider it to be the end of one era, the end of the
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Paleozoic era and the beginning of the Mesozoic era. And this terrible mass
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extinction event is called the Permian-Triassic mass extinction because it is the mass extinction
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that happened at the end of the Permian and at the beginning of the Triassic. So this mass extinction
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was the beginning of the Mesozoic era. The Mesozoic era then started 250 million years ago when that
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mass extinction happened and it ended 66 million years ago, which as we will see
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is also the time of a mass extinction. So mass extinctions are the borders
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between one era and the next. Then the new fauna that evolved after the awful
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Permian-Triassic mass extinction was dominated by reptiles. That's why the
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The Mesozoic era is also called the era of the great reptiles or the era of the dinosaurs.
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During the Triassic period, which is the first period of the Mesozoic era, some reptiles
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evolved into mammals.
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So mammals evolved and appeared at the beginning of the Mesozoic era in the Triassic period.
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And later, after the Triassic period, we have the Jurassic period.
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And in the Jurassic period some dinosaurs evolved into birds.
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As we can see here in this fossil, this fossil is the fossil of a dinosaur that had feathers
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and it was probably able to fly like a bird.
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Scientists cannot really say whether this is one of the first birds or simply a dinosaur
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that is in the branch of evolution that led to birds.
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The fact is that birds evolved from dinosaurs.
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Here you can see an image of a lot of dinosaurs, but not only dinosaurs dominated the world
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at that time.
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There were other reptiles that were not dinosaurs.
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Some were able to fly and they were pterosaurs, like the ones here, and some lived in the
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oceans like mosasaurs, plesiosaurs and ichthyosaurs. This is an ichthyosaur, this is a plesiosaur,
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this is a mosasaur. So all these were reptiles that existed during the Mesozoic era but they were
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not dinosaurs. Their skeleton is very different from the skeleton of dinosaurs and they are not
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considered dinosaurs. Apart from reptiles there were a lot of invertebrates that became very
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numerous in this era and the most characteristic are the ammonites that well which you have already
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seen in the lab that we did with fossils okay the ammonites we saw in the lab were the small ones
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but as you can see some were really big and this is how the animal looked when it was alive okay
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and if we speak about plants during the Triassic and Jurassic periods
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There were seed plants that were very numerous, but those seed plants did not produce fruits.
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The most typical example of these plants that reproduce with seeds but do not produce fruits are the conifers, because they have cones.
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Pines and firs are examples of conifers.
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So these plants were extremely abundant during the Triassic and the Jurassic periods, ok?
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But then near the end of the Jurassic, in evolution, the plants that reproduce with fruits appeared, ok?
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And those plants are called angiosperms.
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Then if we look at the continents, what we see is that during the Triassic, Pangea split into different continents.
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First, it split into two big continents and then those two big continents in turn separated into other continents that were moving
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and they were moving towards an arrangement very similar to the current one, okay?
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During the Mesozoic era, during the era of the dinosaurs, our peninsula, the Iberian Peninsula, was mostly underwater, okay?
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So only a few parts of the Iberian Peninsula were emerged and were dry land.
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Most of it was the bottom of the ocean.
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Then, in the last period of the Mesozoic era, which is called the Cretaceous period,
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the angiosperms, the plants that reproduce with fruits that had appeared at the end of the Jurassic,
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during the Cretaceous period became extremely numerous and diverse
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and in the end dominated the continents, as they do now.
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So the dominant plants now on Earth are the angiosperms.
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They appeared near the end of the Jurassic,
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but it was during the Cretaceous period that they expanded.
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And then we reach the end of the Mesozoic era,
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and as I said, the end of an era means mass extinction event.
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So the third period of the Mesozoic era, the Cretaceous,
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ends with a mass extinction. This mass extinction is not as terrible as the one at the end of the
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Permian. So it is not the worst, but it is the second worst mass extinction event that we know.
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So in this mass extinction event, the last dinosaurs that were not birds died, okay?
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birds are dinosaurs, okay? So not all dinosaurs got extinct, okay? Only the non-avian dinosaurs.
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Then ammonites, pterosaurs, mosasaurs, plesiosaurs, etc. also disappeared. And they disappeared
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suddenly, okay? So this was a mass extinction event. Why did this happen? Well, looks like it
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was because of the fall of an asteroid.
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As probably many of you know,
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this asteroid made the Earth inhospitable
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for animals bigger than a couple of kilograms.
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So big animals got extinct in this mass extinction event.
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The change in the fauna was so big,
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as we can see in the fossil record,
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that geologists considered this mass extinction
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to be the end of an era,
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the end of the era of the dinosaurs,
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of the dinosaurs, the end of the Mesozoic era, and the beginning of the next era, the Cenozoic era.
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The beginning of the Cenozoic era is the Paleogene period. So the mass extinction event
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that eliminated the last non-avian dinosaurs was the mass extinction event at the end of the
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the Cretaceous Period and at the beginning of the Paleogene Period, so it is called the
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Cretaceous-Paleogene Mass Extinction.
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But when scientists abbreviate it, they use older names and also in German, so it is called
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the KT Mass Extinction Event, okay?
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KT Mass Extinction Event represents Cretaceous-Paleogene Mass Extinction, the end of the last non-aging
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So then is the beginning of the Cenozoic era, which is the era in which we live, which started 66 million years ago.
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And in this era, the animals that have expanded and diversified a lot have been the mammals.
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So mammals have become dominant on the planet. They have colonized all the different continents and the oceans.
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But of course, this doesn't mean that only mammals have evolved.
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All living species evolved with time, as we will understand in the future.
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All living species evolved, so the other living things have also been evolving.
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Different kinds of birds, reptiles, amphibians, fish and invertebrates have appeared, evolved during the Cenozoic era.
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One of the famous ones is the gigantic shark megalodon.
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Below you can see a tooth of Megalodon, that gigantic shark, although it was not as big
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as it is depicted in some movies or documentaries.
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It was very big, but it was not as big as a blue whale, for instance.
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The blue whale is the biggest animal we know of.
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Here you have examples of different animals that evolved and expanded during the Cenozoic,
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these animals are now extinct.
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Then, if we speak about geology and the continents,
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during the Cenozoic the continents moved to their current position
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and special things that happened was that
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Africa was moving north, so Africa collided with Europe
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and this created mountains.
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An episode of mountain building is called an orogeny.
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and the orogeny that happened when Africa and Europe collided is called the alpine orogeny
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because it was the origin of the Alps. But not only the Alps, also in the Iberian Peninsula
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we have the Pyrenees, the central system, so Guadarrama, etc. So these mountains have formed
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because of the collision between Europe and Africa. At the same time India, which had been
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separated from Asia until then. India collided with the rest of Asia, this happened around 45
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million years ago, and this gave place to the Himalayas. Then six million years ago
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is the beginning of what we call human evolution. So around six million years ago
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the last ancestor, the last common ancestor between chimpanzees and humans
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existed. Why do we call it the last common ancestor? Because all the
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ancestors of this ancestor have also been common ancestors between chimps and
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humans. This represents the last common ancestor between chimps and
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humans. From this point on, in evolution, some species, species after species after
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species gave place to chimpanzees, or species after species after species gave place to modern humans.
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So this branch of the evolutionary tree, this is the branch from the last common ancestor between
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chimpanzees and humans, and modern humans. So this branch has a lot of branches as well, different
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species that existed in the past that we will study in another another unit like Neanderthals
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or Australopithecus etc so these living things these species that lead to modern humans in
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evolution but do not lead to chimpanzees are called the hominins okay so the hominins are
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all the species in this part of the evolutionary tree all these species are extinct okay all
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hominins are extinct except one species which is our species homo sapiens okay by the way i repeat
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this group of species is called the hominins with an m perhaps some of you have heard the word
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hominid before but hominid is a bigger group of species okay the hominids is a group of primates
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okay a group of primates that is much bigger it includes the chimpanzees and these ancestors of
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chimpanzees it also includes the orangutans the gorillas and of course the humans okay
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so the hominids is not the same as hominins hominids is a very big group of species that
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includes some monkeys that exist now while hominins is a group of species that are all
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extinct except humans and it is specific of the evolution towards humans okay and finally we're
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about to finish another special thing of the sinusoic era is that in the last period of the
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sinusoic era which is called the quaternary period and is divided into epochs we have the current
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ice age. What is an ice age? From the point of view of glaciology an ice age is a time
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in which there are permanent ice caps on the poles. So now there is permanent ice on the
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north pole and on the south pole. So from the point of view of glaciology we live in
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an ice age. And during ice ages there are times that are extremely cold and they are
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called glaciations or also glacials and there are times in which there is permanent ice on the poles
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but they are not so cold so the ice caps are not so big then those periods that are not so cold
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are called interglacials okay so we now live in an ice age but we live in an interglacial of this ice
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So we live in an ice age but not during a glaciation.
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So this current ice age, this current cycle or succession of glaciations and interglacials
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started around 2.5 million years ago.
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So from the point of view of glaciology we live in an ice age which started 2.5 million years ago
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although we live in an interglacial of these ice age.
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Okay, and then with this,
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I have finished speaking about the Fannyrozoic union.
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Thank you for your attention.
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