Well, welcome to week three of the American Museum of Natural History's course on evolution. So today we'll talk very, very briefly about the origin of life. But then, I want to spend more time looking at the patterns of diversity across time and space and large-scale relationships of life. mainly, what are the, what's the tree of life and when did things evolve? Evolutionary systems are really old. And so, I think, one of the keys in teaching evolution, is having students kind of understand deep time. So the Big Bang and the Universe is, is aged to be 13.82 billion years old. The solar system that we live in is 4.6 billion, and Earth itself, is 4.54 billion years old. And the oldest evidence we have for life is 3.5 billion. So, only about 1.2 billion after Earth was formed, and cooled down, and sort of solidified, life was here. And it's probably a little well older than 3.5 billion. Now, I'm not an expert on the origin of life. And, the origin of life research is, which is very, very huge is mostly about biochemistry and physical chemistry. But large-, what happened, basically, is that we define life as something that's self-replicating. the Earth cooled and large bodies of water began forming 4.5 to 5 billion years ago. and water and organic compounds accumulated. So there's, there's lots of carbon dioxide, carbon monoxide, in the air and these formed polymers. And eventually some of these polymers, and this is taking place over a long period of time. a lot of these form auto-catalytic functions, so they, they, they helped catalyze their own kind of reactions. And they be, molecules just became increasingly, increasingly complex. And what scientists think is that there were kind of nucleic acid-like analogs which eventually evolved into developed it into an RN-, RNA world, which is also heredity, and then a DNA world, which is, of course, heredity. And, all of this happened ov-, over many hundreds of thousands, hundreds of millions of years, maybe even a couple of billion years, we just don't have record much beyond 3.5 billion years ago. But we do kind of think we understand from looking at the tree of life, that early life was probably thermophilic. In other words, because earth was hot the, these early life forms, bacteria-like lifeforms, were likely to be thermophilic. Now, if we look at the whole range of life on Earth, and we know that fossil record best from the marine animal fossil record. But life began this diversity began around 500, 550 million years ago in the Cambrian and evolved over time. So, so, it, it, it had a kind of quasi-steady state diversity. It, it, it arose up very, very quickly, and then had this steady-state diversity. And mostly of that steady state was due to these mass extinction events. Then there was this major Permo-Triassic extinction event, which we'll talk about in the next lecture. And then, there was from about 250, 260 million years ago, there was this almost exponential increase in diversity to the present. Except for this Cretaceous-Paleogene dinosaur extinction event we'll call it. but life has been diversifying exponentially almost for the last 250 million years, a quarter of a billion years. In the next few slides we're going to survey the great tree of life in very broad general terms, and we'll start toward the base of the tree. Our science tells us that we have three major groups of organisms. one is the bacteria and the second group is the archaea, which are bacteria-like, what we call extremophiles because, because many of them live in very hot environments, such as hot springs. And then, there's the Eucarya, which includes virtually all the organisms that we see in our day, day-to-day life. And we bah-, think that this started around 3.5 million, billion years ago because that's when we find our first filamentous microbes. And this node probably does go back older than that. And, bacteria and archaea are both very, kind of simple cellular structure single organisms. Whereas the eukaryotes begin to develop different cellular components. They, they have cells with a nucleus surrounded by a double membrane. And there's a whole host of other cellular processes that differ between archaea and eukaryote versus the bacteria, and then within the eukaryotes and ar-, ar-, archaea. Again, we have bacteria and archaea and then, in green here, we have all of the eukaryotes organisms. And at the base of this eukaryote tree, are lots and lots of single cell organisms including things like leish mania, which cause leishmaniasis. Then there are things like giardia which which causes a lot of it gastrointestinal problems. And as we, as we look at this tree then, plants, fungi and animals are so-, are, are, are more closely related than they are to these, to these groups. And we do know that this clade here, this group of organisms, these eukaryotes started at least 1.8 billion years ago. Now as we move up, we, we can see that up the tree, we're now looking at the big picture of plant phylogeny. And the first group off here are the red algae. Now not all algae are the same, there's a, a real group called green algae. And then there's other groups that are also al-, algo-like and green. But this means here that these developed chlorophyll in, in, in their cells, but red algae didn't, and red algae go back to about at least 1.2 billion years. So when you go out to the seashore, and you see red algae like these, you can, you're looking at groups that are very, very ancient. Up in the, up in the going up the tree chlorophyll A and B develop. They, they developed the ability to store carbohydrates as starch, and many, many groups evolved. Like liverworts, mosses, hornworts, and, and these club mosses. All of which, many people can see very easily by going into some woods that is sort of wet and moist and the northern woods are perfect to see all of these different kinds of groups. And then, there developed this group here, with the ferns and the horsetails, and then the wonderful cycads, and the confiers, the pine trees, the firs, all these so called gymnosperms. And then we have the flowering plants. Now, all of these are fairly old, as I said that the split between red algae and everything was 1.2 billion years. But, land plants themselves have been around for 420, 470 million years and all of these groups are very, very old. And they go back about 280 million years. Then when we get into the angiosperms, in other words, the flowering plants, there are two big, big groups. Very, very diverse group called the eudicots and it's all because of the, the, the seed, the seed shapes. So the dicots have two wings on their seed, monocots have one wing on their seed. But these are very well-known groups like orchids, and irises, and palms, and grasses. And, and then the eudicots include poppies, and, and cacti, and all of these composite plants. That, these, these wonderful flowers that have many, many, many leaves coming out of the of the, the central part of the plant. So, these all evolved somewhere in the neighborhood of 135, 125 million years ago. Now, this is going to be a very, very quick picture of what we call the bilateria. In other words, these are, these are organisms that are bilaterally symmetrical, like you and I are bilaterally symmetrical. But metazoans, or animals as they're normally called we are developing bigger, and bigger, and bigger trees of of life for all animals. And I'm just going to give you a very, kind of a quick overview here. At the bottom of the tree are things like sponges, and the Cnidaria, which include the hydras, and the jellyfish. And then we come up into various kind of worm-like groups, nematode worms. and then we, we get into these big groups, this big, big group. These are the, what are called Ecdysozoa, and that's because they shed their, their skins and grow a new one. So we see butterflies and, and moths and they, they shed they shed their skins through ecdysis, and this include the insects. And insects are actually modified crustaceans. We're finding that out now, and then there are many, many groups of centipedes and millipedes, scorpions, spiders. And then we have a group called the Spiralia that incoos-, includes the annelids, which are the ground worms, the worms that we see out here, earthworms, I mean mollusks. And then various platyhelminth groups including flatworms and, and groups of worms that actually cause human disease. And then we finally get up to the groups that include the chordates. In other words, the vertebrates, the acorn worms, and echinoderms. And then, let's, let's end up with the the groups that we know the best, the vertebrates and the tetrapods. So, vertebrates, those with a backbone, start off over 520 million years ago. So, at the time of the Cambrian explosion, most of, most of these major groups of organisms were evolved very, very rapidly. And have, have been evolving for many, many hundreds of millions of years. So, there are, are groups in the Cambrian that look very similar to things like hagfish but, but they, we, we know they're kind of vertebrates because they, they seem to have backbones. But, we have all the sharks and the rays, and then we have the ray-finned fish, and the lungfish and the coelacanth fishes, which are now not very diverse. But we ge-, when we get up into the tetrapods, which arose around 350 million years, then we get into the, the very well-known groups now. These are all recent groups, and we could put in many, many, many other major groups. fossil groups as, as almost all of you know, there are theropod dinosaurs here closer related to, to birds. So I, I want to leave you with a couple take home messages. And I think these are really very important for, for students. So, life on earth is very old. And all of these evolution systems are very old. And life is exceedingly diverse. And it's diversified a lot in the last 250 million years. And, and we are now we have, the Earth teems with life right now. And, we can see that life is arranged in this tree of life, in this, these hierarchical relationships, of one group within another group, within another group. And then, we, as we will talk about in our upcoming lectures, knowing the relationships of these organisms is a very, very powerful tool for comparative biology, for applied biology. And for actually improving human well-being.
