The History of Life, the Universe and Everything or What do you get when you multiply six by nine Chapters 17 (skim) and 18
The Origin of Life The problem: Life begets life. There must be a beginning, but how? We know the world is about 4.5 billion years old We know the oldest rocks are about 3.8-4 billion years old We know that there are fossils 3.5 billion years old Conclusion: Life arose very quickly (1/2 billion years or so)
What is life? Defining life is fraught with problems. Philosophically we want to be qualitatively different from a salt crystal! Life: Processes and controls energy Reproduces Evolves Phenotypic variation Heritability Differential fitness
The big problem is heritability It is easy enough to create self replicating objects (crystals) It is easy to have phenotypic variation among those objects It is easy to imagine them having differential fitness. Heritabilility is the issue. DNA cannot replicate itself without proteins Proteins require DNA/RNA to be produced.
Some Considerations RNA can form ribozymes: RNA that can replicate RNA. (It doesn t replicate itself so well) The efficiency of ribozymes is greatly enhanced if it binds to a substrate such as clay The environment of the world at the dawn of time was a reducing atmosphere very different from the modern world. Operin-Haldane model: HCN, H 2 0, CO 2, H 2, N 2, NH 3, Energy. Under these conditions nucleotides and amino acids will
One view of the Evolution of Life How ever it happened, by 3.5 billion years ago life was common.
Life on Mars Why is the current debate over life on Mars so important. Panspermia hypothesis (I consider this unlikely) Much more important: Very likely life on Mars (if it turns out to be true) is an independent evolutionary event. If life evolved twice in this solar system, it must be very common in the universe With a replicate we can start asking what is the same and different between different independent evolutions of life.
Deep Phylogenies Based on small subunit RNA (a very slowly evolving gene) Note the split between Bacteria and Archaea Note that Protists are split all over the place!
Horizontal Gene Transfer This is particularly important in bacteria (and archaea) Four billion years ago that s all there was!
However it happened life arose What we have been talking about is the period from 4.5 billion years ago to 0.550 billion years ago. 4 billion years to get life, 1/2 billion more to get to the moon! Things have been accelerating.
Several themes Evolution of life took a long time Evolution since then has gone very fast, perhaps accelerating There are long periods of stasis At one level (phylum level) diversity has not increased At other levels (family level) diversity has greatly increased Random events have played a huge role in evolution Progress is hard to define.
The Precambrian The Precambrian was a long time ago, fossils are spotty. There were definitely diploblastic Radiata There may have been Bilateria There may have been precoursers to all modern phyla
Stochasticity in Evolution Stephen J. Gould 1941-2002
The Cambrian Explosion QuickTime and a Photo - JPEG decompressor are needed to see this picture. QuickTime and a Photo - JPEG decompressor are needed to see this picture. Animals of the Burgess Shale At the start of the Cambrian all animal Phyla currently in existence were already present (and maybe some that don t
There may even have been Vertebrata! Well, actually, a primitive jawless fish that would have been transitional, and more closely allied with Lampreys
Ordovician QuickTime and a GIF decompressor are needed to see this picture. QuickTime and a GIF decompressor are needed to see this picture. complex invertebrates First vascular land plants (actually Silurian)
Devonian QuickTime and a Photo - JPEG decompressor are needed to see this picture. Vertebrates (and JAWS) appear. Changes the world forever!
Carboniferous QuickTime and a Photo - JPEG decompressor are needed to see this picture. Plants figure it out, and fully invade land. Earliest seed plants
Permian QuickTime and a GIF decompressor are needed to see this picture. QuickTime and a Photo - JPEG decompressor are needed to see this picture. Amphibians fully invade the land, reptiles start to appear
Then a Catastrophe Occurs By the End of the Permian/beginning of the Triassic it is estimated that 96% of all marine fauna went extinct. It is likely terrestrial extinctions were just as bad.
It happened too long ago to really know the What Happened? The Permian extinctions was the most serious extinction event in the history of the earth. One possibility: It was a major event from outside. A change in the suns intensity, a large asteroid
Shoemaker-Levy crashed into Jupiter in July 1994
Tswaing Crate Gauteng, South Africa 200,000 years old 300000 kg, moving 16 km/sec Arizona Meteor crater Arizona 50,000 years old several hundred thousand tons
Two points to consider (1) How would life have been different if the asteroid had not h In other words, what role have stochastic events played in the history of life? This was Gould s big point. (2) Are we currently in the middle of another mass extinction Signs would seem to say yes, but it does not appear as extreme as the Permian/Triassic, or K/T extinctions.
The Effect of the Extinctions One of the main effects of the mass extinctions must have been to open up a huge number of niches. The effect of this is to allow for adaptive radiations to occur. With amphibians out of the way it was hardly surprising that reptiles would radiate into the empty niches. The Triassic becomes dominated by early reptiles. The same is true for plants. With spore plants out of the way the Triassic becomes dominated by seed plants (gymnosperms)
Triassic, Jurassic, Cretaceous The age of reptiles. Colonization of land is complete. Flowering plants arise, as do mammals. Both are rare.
The K-T boundary we do know about. The extinction of the dinsaurs was caused at least in part by the impact of an asteroid.
The K-T Boundary (Cretaceous-Tertiary Boundary)
Again, this opened up niches The extinction of the dinosaurs gymnosperms opened up niches leading to the radiation of the Mammals and flowering plants. Note: Birds are really dinosaurs, so not all dinosaurs really went extinct!
Tertiary -- Paleocene - Oligocene QuickTime and a Photo - JPEG decompressor are needed to see this picture. The time of BIG mammals. The so-called megafauna
What caused the extinction of the megafauna Not all extinct -- Large African mammals, Condors, whales Some evolved to be smaller -- Bison QuickTime and a Photo - JPEG decompressor are needed to see this picture. copyright of Heartland Associates
The cause appears to be Humans QuickTime and a GIF decompressor are needed to see this picture. Extinctions closely follow human colonization ancient humans were known hunters of megafauna The only continent not to experience HUGE extinctions is Africa, where humans evolved (and which has rampant disease, especially tryptosomiasis, or sleeping sickness)
Causes of the current mass extinction Overhunting Mammoths Stellars Sea cow Bison Increased use of resources by humans Habitat loss Deforestation Habitat Fragmentation Pollution & Environmental Modification Invasive Species
Evidence of humans hunting mammoths QuickTime and a GIF decompressor are needed to see this picture. QuickTime and a GIF decompressor are needed to see this picture.
Stellars Sea Cows QuickTime and a GIF decompressor are needed to see this picture.
Finally: Stasis The final commonality of the history of life is long periods of apparently no phenotypic change in a species.
Stasis Nobody really knows what causes long term stasis It is NOT lack of genetic variation More likely it is ecological stability May have to do with competition constraining change. Note that the sudden changes of punctuated equilibrium are desperately slow from a population geneticists perspective!