4.1. Cycles of Radiation and Extinction

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Do curso por University of Illinois at Urbana-Champaign

Emergence of Life

58 classificações

University of Illinois at Urbana-Champaign

Emergence of Life

58 classificações

How did life emerge on Earth? How have life and Earth co-evolved through geological time? Is life elsewhere in the universe? Take a look through the 4-billion-year history of life on Earth through the lens of the modern Tree of Life! This course will evaluate the entire history of life on Earth within the context of our cutting-edge understanding of the Tree of Life. This includes the pioneering work of Professor Carl Woese on the University of Illinois Urbana-Champaign campus which revolutionized our understanding with a new "Tree of Life." Other themes include: -Reconnaissance of ancient primordial life before the first cell evolved -The entire ~4-billion-year development of single- and multi-celled life through the lens of the Tree of Life -The influence of Earth system processes (meteor impacts, volcanoes, ice sheets) on shaping and structuring the Tree of Life This synthesis emphasizes the universality of the emergence of life as a prelude for the search for extraterrestrial life.

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Week 4 - Paleozoic Life After the Advent of Skeletons

This week, you'll learn more about the Cambrian Explosion, which led to the development of external hard skeleton components at 542 million years before present. The initial successes of the invertebrates were shortly followed by the appearance of vertebrates with internal skeletons. Life then utilized these newfound evolutionary capabilities, beginning distinct cycles of radiation, diversification, and extinction, which define the three great Eukarya faunas of the Phanerozoic.

4.1. Cycles of Radiation and Extinction7:33

4.2. Cambrian Explosion3:43

4.3. Cambrian Fauna: Origin of Vertebrates14:40

4.4. Burgess Shale Experiment5:38

4.5. Invertebrates: Successes of Life Without a Backbone18:26

4.6. Paleozoic Fauna12:06

4.7. Vertebrates: Successes of Life With a Backbone3:28

4.8. Evolution of Jaws and Perfecting Predation13:15

4.9. Heavily Armored Fish Without Jaws6:44

4.10. Fish Evolution: Hook, Line, and Sinker10:16

Conheça os instrutores

Bruce W. Fouke, Ph.D.
Director of the Roy J. Carver Biotechnology Center
Department of Geology, Department of Microbiology, and Institute for Genomic Biology

[SOUND]

[MUSIC]

I'm Bruce Fouke from the University of Illinois Urbana-Champaign.

We need to put together a framework to understand how all living organisms

are related to each other, but also how they have systematically and

sequentially replaced each other or moved forward through geological time.

And so, we need to think about the idea that nature keeps running experiments

of the origination, and the evolution and

proliferation of organisms within a given ecological environment.

And then, having that environment change.

And response of the organisms is to have either all or

most of those organisms go extinct.

Once organisms go extinct, they're replaced by other organisms that can do

better in that environment than they did, because they didn't have

the characteristics they needed, the characteristics of reproduction,

seeking food, being able to protect themselves.

All the things that make it so

possible to succeed and be alive in an Earth environment.

Organisms have those characteristics.

The Earth environment is structured such that they can do

well until the Earth environment changes.

And then, once that environmental change takes place,

then those organisms are the ones who don't do well.

They go extinct, and they get replaced by something else.

So, in that context, the basic tree of life

that was established by Professor Carl Woose at the University of Illinois,

that basic tree of life is a three fold structure.

There are three basic branches.

The branch of the bacteria and the branch of the archaea, the first two branches,

those are single cell organisms that reproduce asexually.

Then, the third branch of life are the Eukarya.

The multi-cell organisms that reproduce sexually, for the most part.

So, we want to think about that being the roadmap of life.

Then, within those three branches, we want to think about how has life

changed systematically through the history of Earth, from very early Earth,

when Earth was extremely different from what it is now, chemically,

physically, and biologically, too.

And Earth that we know of in the modern-day environment.

So, we want to put the template of a changing Earth on top of the three

branches of life.

And the way we do that, then, is as we move up the three branches of life

then we can evaluate the upper parts of the tree and how they branch.

Each of those branches in the upper parts of the tree of life are representing

changes through evolutionary biological processes that create and

form different kinds of life as time goes forward.

So, what we want to do is look at an Earth where we were moving from

having single cell organisms only, to multi-cell organisms.

And the advent of the incredible radiation and diversification of these Metazoans,

the multi-celled organisms, and having the Metazoans go from

having an organism that has no skeleton to an organism with skeleton.

Because once the skeletons were formed by Metazoans, and

that's what we define as the Cambrian Explosion at 543 million years before

present, everything changed in terms of the development and

the structure of how Metazoans could interact with their environment.

So, the way we do that is that we consider, first of all,

what were the primary natural experiments that nature had run in order to

see how these things fit together in the puzzle pieces.

And so, one of the first ones that were run by nature

was called the Ediacaran Fauna.

And this was a group of organisms that were Metazoans, they had no skeletons.

And they came on board, they originated, they radiated

right after a catastrophic event in Earth history called the Snowball Earth.

This group of unique organisms, though, they themselves went extinct.

They were relatively short-lived, and

they were replaced by a group of organisms that were Metazoans that had skeletons.

And the skeletons at first were all exoskeletons.

They were on the outside of the body of the organism.

And then, as time evolved through the Phanerozoic, then we saw the advent of

Metazoans being able to synthesize and secrete a skeleton that was interior.

And we call those vertebrates.

So, we move from an invertebrate Earth to an Earth that had both vertebrates and

invertebrates.

And we see how that structural design feature allowed them

to really do well in these evolving Earth environments,

both in the terrestrial environment and in the oceans.

Within that grouping of geological time that goes from the 543

million year Cambrian explosion through the modern, we call that the Phanerozoic.

And that Phanerozoic is broken into three primary groups of what we call Fauna.

And the Fauna are the groupings of animals.

The first grouping of animals was called the Cambrian Fauna.

The second grouping of animals was called the Paleozoic Fauna.

And the third grouping of animals was called the Modern Fauna.

And then, the changes sequentially going from the Cambrian Fauna

into the Paleozoic Fauna into the Modern Fauna, it was benchmarked.

It was truncated.

t was defined by Earth processes.

One of the most important of which was meteor impacts.

So, when large meteors slammed into the Earth,

they caused a lot of organisms to go extinct.

And each time those massive extinction events took place,

then nature would respond by, once the catastrophe took place and

some geological time went forward, then new organisms evolved and moved into those

ecological zones that were previously inhabited by another type of organism.

And we see that there's this basic threefold structure of having organisms

respond to new and open ecospace in which they could radiate and

evolve, and then have the whole system reset by meteor impacts.

So, the Cambrian Fauna, the Paleozoic Fauna and the Modern Fauna.

And that's the template of the evolution of multicellular

organisms with skeletons, both internal and external.

That defines and sculpts the shape of one of the primary three

branches of life, which are the Eukarya.

Moving forward from here, we want to then start to look at the idea that

that Eukarya branch in history was also interfacing all the time,

not only with a changing planet, but also with microbes, bacteria and archaea.

And one of the great challenges of science is to be able to understand how all these

multiple branches of life are developing, and how they interact with each other

to influence each others ability to survive in an ongoing changing planet.

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