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Evolution. Chapter 25. Great Idea: All life on Earth evolved from single-celled organisms by the process of natural selection. Chapter Outline. The Fact of Evolution Chemical Evolution Natural Selection and the Development of Complex Life The Evolution of Human Beings.
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Evolution Chapter 25 Great Idea: All life on Earth evolved from single-celled organisms by the process of natural selection.
Chapter Outline • The Fact of Evolution • Chemical Evolution • Natural Selection and the Development of Complex Life • The Evolution of Human Beings
How did life start- origin of life. • How did the astonishing variety of life that we observe come about. • Fossil record. • Fossils- minerals replace the natural materials of the “hard parts” of organisms. • Mass extinction. • Genetics
The Origin of Life What are the properties of living systems? 1. Self duplication with information transfer. 2. Discrete change. Living systems are systems that reproduce themselves closely, but that mutate as well and can reproduce their mutations.
The word evolution simply means a change in genetic content. Populations evolve but individuals do not.
The Fact of Evolution • Evolution • Ongoing process of change • Scientists accept evolution as fact • Debate various theories
There are two approaches to tracing species: 1. Examine the fossil record - Paleontology 2. Examine the genes of living organisms - Molecular genetics
The Fossil Record • Fossils • Organism’s hard parts preserved • Turned to rock • Replaced by minerals • l • Fossil record • Fossils found, catalogued & analyzed • Shows transitions • Incomplete • Three key ideas • Older fossils more different • Increasing complexity with time • Most species have gone extinct
The Biochemical Evidence • DNA • Evidence for evolution • Changes slowly • Also compare amino acid sequences • Cytochrome C • Humans and chimps identical • Rattlesnake 86% overlap
Evidence from Anatomy:Vestigial Organs • Vestigial organs • Internal features • No useful function • Example • Appendix: humans • Wings: penguins • Hind legs: whales
Life requires: Carbon, Nitrogen, Oxygen, Hydrogen Reducing Atmosphere: Carbon - CH4 Nitrogen - NH3 Hydrogen, Oxygen - H2O Non-reducing Atmosphere: Carbon - CO2 Nitrogen - N2 Hydrogen, Oxygen - H2O
There are considerable questions regarding the atmosphere of the primitive Earth. It is clear that there was no free oxygen. Free oxygen did not occur until living organisms evolved photosynthesis.
The Miller-Urey experiment. Several of the chemical compounds thought to have been present on the early Earth were mixed and subjected to electrical discharges. Within a few weeks, amino acids had formed. The spark is like lightning!
Stanley Miller's experiment, (1953) The spark is like lightning! Carbohydrates, bases, and amino acids formed
Some Origin of Life Scenarios 1. Life began in hydrothermal vents 2. Inorganic catalysis was important a. Clay minerals were the first living things b. Nitrogen fixation by oxides 3. Extraterrestrial origin of life
RNA Enzymes • Early life was simpler • RNA catalyzed reactions • Created proteins • Proteins led to DNA
The Window of Opportunity • Chemical processes • Occurred rapidly • Recent discoveries • Schopf • Evidence of life 3.5 billion years ago • First Cell • 4.0-3.5 billion years ago
The First Cell • First cell • No competition • Multiplied rapidly • Special characteristics • 20 amino acids
Black Smokers • Black Smokers • Deep-ocean floor • Vents of mineral rich hot water • Diverse ecosystem • Most primitive bacteria • Hydrothermal zones • Site of life’s origin? • Protected • Ideal chemical environment
Natural Selection • Darwin • Natural Selection • Variation in populations • Some variation heritable • More individuals born than will survive • Adaptation • Artificial selection
The Story of Life • First cell • Natural selection • mutations • Mutations • Most not beneficial • Environment • Impacts evolution • Eukaryotes • Colonies • Hard Shell • Cambrian explosion
Mass Extinctions and the Rate of Evolution • Rate of extinction • 10%-20% extinct in 5-6 million years • Mass extinctions • 30%-90% extinct • Mechanisms • asteroid • Evolution • Gradualism • Punctuated equilibrium
Mass extinction The geological record show a number of instances in which the number of different species dropped dramatically These are mass extinctions brought about by some change in the environment: Meteor impact Global climate change Glaciation (Ice ages) Continental Drift Global warming (rise in sea levels)
The diversity of life on Earth has not increased steadily, but has gone through a series of sharp changes. This graph of marine animals in the fossil record is indicative of the overall growth in families and of extinctions. The extinction of the dinosaurs is labeled 5.
The location of the giant crater near the Yucatán Peninsula in Mexico. The effects of the asteroid’s impact were recorded in rocks as far away as the red dashed circle.