2.4. Evolution of the Tree of Life

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From the course by University of Illinois at Urbana-Champaign

Emergence of Life

57 ratings

University of Illinois at Urbana-Champaign

Emergence of Life

57 ratings

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.

From the lesson

Week 2 - The Tree of Life and Early Earth Environments

The advent of life on Earth came about as a result of a remarkable confluence of physical, chemical, and biological processes, all of which were intrinsically linked to rapidly changing early Earth environments. Within this context, cutting-edge approaches in molecular phylogeny by Professor Carl Woese revealed new understandings of the emergence of life and the possible distribution of life within the cosmos. All this and more will be explored in this week's lessons!

2.1. The Scientific Inquiry of Carl Woese8:00

2.2. The Place of Carl Woese in Evolutionary Biology8:24

2.3. Revolution of the Tree of Life7:41

2.4. Evolution of the Tree of Life6:42

2.5. How Did Life Emerge?5:25

2.6. The Genetic Code and Evolutionary Theory7:23

2.7. Throwing Rocks at Earth: The Martian Meteorite10:46

2.8. Microbial Mats and Stromatolites: Laying Down On the Job6:49

2.9. Oxygenation of the Atmosphere5:15

2.10. Snowball Earth; It Did Freeze Over!8:31

Meet the Instructors

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

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So the advent in 1977 of molecular phylogeny recast and

restructured fundamentally how we look at the emergence of life on planet Earth.

Now an important context for our modern day understanding of the emergence of

life is to look at how different and how drastically changing and evolving itself,

the whole concept of evolution has been over the last 150 years.

And, in fact, even deeper into human history than that.

So what we want to do is take a look at the changes in evolutionary thought and

how people had tried to graphically structure the tree of life.

And then see how fundamentally different from that then,

that the departure is for the results of Carl Woese and

his colleagues here at the University of Illinois.

So we need to start all the way back actually

in 1674 when Antonie Van Leeuwenhoek,

who was a scientist in Holland, developed the first microscope.

And that first microscope was actually a brass plate with a few very crude

lenses and a setting screw that allows you to change the angle and

therefore the magnification of the lenses.

Well Leeuwenhoek is very famous because of that development of the microscope,

and he is the first one who actually published an observation

that there was life on a very small scale.

That microscope was strong enough for

him to see one micron cells, some of which were bacteria.

Some of them were eukaria,

the more advanced forms of cellular life on the planet, and

that publication in the perceives of the Royal Academy of Science was a benchmark.

It was the first time that human beings had seen life

active at that kind of scale.

The next step in the process was about a hundred years later,

and in 1735, Linneaus who was a Swedish scientist decided to use primarily

the observations of the diversity of life on planet Earth for morphology,

the size, the shape, the color, some of the attributes of how the organisms lived.

Try to use those to break all of life into pieces and

compartments that could be used to look at the structure.

And eventually, the historical evolution of life.

And Linneaus came up with two kingdoms, he called them.

One were the animals and one were the plants.

And so Linneaus was critically important for developing the ability to

describe morphological differences and move forward with that

kind of what we call taxonomy, that descriptive taxonomy of what was living.

Well and again about another 100 years plus and passed in and in 1866 Haeckel

decided to start structuring not only morphology as you can see with the eye but

also some morphologies you could see under the microscope.

Now remember this is long, long before the genetic tools were available.

So this was using whatever tools of observation were possible at these times.

And what Haeckel put together was a very different kind of tree.

Again, Linnaeus had animals and plants.

Haeckel's, you can see from this, also had plants and had animals, but

also had another small group of organisms called the protist and these protists were

single cells or sometimes multiple cells but they were small and they moved around,

and you could see they had these different morphological features.

They had some different colorations.

But then also, he broke things into another group called the Monera and

the Monera were what we call in the present day the single cell microbes that

eventually were bacteria and archaea.

So the Monera was kind of a loose grouping of single celled organisms,

the protist were the more complex yet still small organisms and

we kept with the plants and the animals.

Well, another 100 years plus past, and

there was a benchmark work by a scientist named Whittaker in 1969.

And you can see from the Whittaker tree of life there was this concept of having

eukaryotes and that was one of the earlier times that eukaryotes have been coined.

And then we had prokaryotes.

And those were all the single-celled small organisms.

So going from prokaryotes to eukaryotes, and

you can see that tree makes it a very linear progression of the two implying

that eukaryotes evolved directly from the prokaryotes.

And all the prokaryotes.

And you can see some of the same names were kept.

The Monera were part of that Prokaryote group.

And the protist again these more complex small single cells.

So the Whittaker tree is actually what is still used in a lot of applications

within science today and can still be found in some textbooks.

Well the advent of the 1977 publication by Wilson and

Fox and then the ensuing publications especially Woese et al.

1990 reset fundamentally the stage of how we understand that the structure

of the evolution of life on this planet took place.

So all these came together to produce a drastically

different looking tree of life.

And in this tree of life you can see that we're hovering in a helicopter,

if you will, looking down at the upper most branches of that tree of life.

And in the middle we have an origin, we have a root or a stalk versus having these

three branches, bacteria, archaea, and eucarya coming up and out.

The importance is that the context of the history of the evolution

of the idea of a tree of life itself really sets the stage for

us because it compares and contrasts what was thought of as being simpler life and

more complex life and what came first and what came second.

Instead of some of those paradigms and hypotheses that were put up and

very reasonably based on morphology, the genetic tool, the molecular phylogeny,

allows us to quantify these relationships and

look deep into time to see how a diversion this planet is structured.

In terms of its capabilities of lifestyles, ecology, but

then even more importantly, its genetic composition.

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