Chapt15 Lecture

The Fossil Record Reveals the History of Life on Earth 15-

15.1 The geologic timescale is based on the fossil record Because all life-forms evolved from the first cell or cells, life has a history that is revealed by the fossil record The geologic timescale depicts the history of life based on the fossil record Divisions of the Timescale - the timescale divides the history of Earth into eras, then periods, and then epochs The epochs have the shortest time frames The three eras span the greatest time Paleozoic, Mesozoic, and Cenozoic Dating Within the Timescale - the timescale provides both relative and absolute dates References to events during a timescale are in relative time Dates given in millions of years (MYA) are in absolute time 15-

Limitations of the Timescale Evolution is not a series of events leading only from the first cells to humans Timescales list mass extinctions, but don’t tell when specific groups became extinct Extinction is the total disappearance of a species or a higher group Mass extinction occurs when a large number of species disappear in a few million years or less 15-

APPLYING THE CONCEPTS—HOW SCIENCE PROGRESSES 15.2 The geologic clock can help put Earth’s history in perspective 15-

15.3 Continental drift has affected the history of life Continental Drift We now know that continents are not fixed Their positions and the positions of the oceans have changed over time Plate Tectonics Earth’s crust is fragmented into slablike plates that float on a hot, liquefied metallic core that lies directly beneath the Earth’s crust At deep oceanic ridges, seafloor spreading occurs as molten mantle rock rises and material is added to plates Seafloor spreading causes the continents to move and causes the Atlantic Ocean to get wider Where the plates meet, the forward edge of one sinks into the mantle and is destroyed, creating a subduction zone When continents collide the result is often a mountain range 15-

Figure 15.3A The continents have drifted through time 15-

15.4 Mass extinctions have affected the history of life At least five mass extinctions occurred throughout the history of life End of the Ordovician, Devonian, Permian, Triassic, and Cretaceous periods Causes of Mass Extinctions Meteorite - A piece of rock from outer space that strikes the Earth and creates a crater The date of a large crater on the Yucatán Peninsula in Mexico corresponds to the timing of the K-T extinction Climate Changes - Severe climate change can cause an extinction Marsupials died from the cold as the continent of Antarctica drifted to the South Pole Human Activities - Some scientists believe we are currently in the midst of a mass extinction due to human activities This modern-day extinction is due to our manipulation of the environment, such as modern agricultural methods and industrialization and its demand for energy and the resultant global warming 15-

Figure 15.4 Mass extinctions 15-

Systematics Traces Evolutionary Relationships 15-

15.5 Organisms can be classified into categories Classification is the grouping of extinct and living species into the categories: domain , kingdom , phylum , class , order , family , genus , and species Taxon (pl., taxa) - group of organisms that fills a particular category of classification Character - any trait that distinguishes one group from another Taxonomy - the science of naming species 15-

Scientific Names They are called binomial because they have two parts The first word is the genus, and the second word is the specific epithet Example: Parthenocissus quinquefolia It preferable to use an organism’s scientific name instead of the common name The scientific name is based on Latin, which doesn’t change Common names often differ between countries and even within the same country 15-

Figure 15.5 Hierarchy of taxa for Parthenocissus quinquefolia 15-

15.6 Linnaean classification reflects phylogeny Systematics - study of the diversity of organisms at all levels of biological organization Phylogeny - evolutionary history of a group of organisms Often represented by a phylogenetic (evolutionary) tree, a diagram indicating common ancestors and lines of descent Each branch point in a phylogenic tree is a divergence from a common ancestor, a species that gives rise to two new groups 15-

Derived and Ancestral Characters Derived Characters - individual characteristics unique to a group of organisms 15-

Ancestral Characters - those shared by a common ancestor 15-

Figure 15.6 Linnaean classification and phylogeny 15-

15.7 Certain types of data are used to trace phylogeny Fossil Record - It is possible to use the fossil record to trace the history of life in broad terms One of the advantages of fossils is that they can be dated, but it is not always possible to tell which group a fossil is related Homology - character similarity that stems from having a common ancestor Homologous structures are related to each other through common descent Molecular Data - systematists assume that when two species are closely related, a comparative study of their DNA will show few differences in base-pair sequences Molecular Clocks - When nucleic acid changes are neutral and not tied to adaptations they accumulate at a fairly constant rate These changes can be used as a molecular clock to determine when two species diverged from a common ancestor 15-

Deciphering homology can be difficult because of convergent evolution Convergent evolution - the acquisition of the same or similar characters in distantly related lines of descent Similarity due to convergence is analogy Analogous Structures have the same function in different groups, but do not have a common ancestry Example: the wings of an insect and the wings of a bat are analogous Parallel evolution - the acquisition of the same or a similar character in two or more related lineages without it being present in a common ancestor Example: the flying squirrel (a placental mammal) and the flying phalanger (a marsupial) 15-

Figure 15.7B Convergent evolution 15-

Figure 15.7C Molecular data 15-

15.8 Phylogenetic cladistics and evolutionary systematics use the same data differently Phylogenetic cladistics - a method of determining evolutionary relationships based on shared characters derived from a common ancestor Uses shared derived characters to classify organisms and arrange taxa in a diagram called a cladogram, which traces the evolutionary history of the group being studied In a cladogram, a clade is an evolutionary branch that includes a common ancestor, together with all its descendant species 15-

Figure 15.8A Data for constructing a cladogram 15-

Figure 15.8B In a cladogram, a clade (colors) contains a common ancestor and all its descendents with shared derived characters 15-

Evolutionary Systematics The traditional method of using characters and judgment to classify and determine evolutionary history Evolutionary systematists mainly use structural data and the Linnaean system to classify organisms and construct phylogenetic trees 15-

Figure 15.8C Evolutionary systematics versus cladistic view of reptilian phylogeny 15-

The Three-Domain System Is Widely Accepted 15-

15.9 This text uses the three-domain system of classifying organisms Domain Bacteria Bacteria are a prokaryotic group that is so diversified and plentiful they are found in large numbers nearly everywhere on Earth The cyanobacteria are photosynthetic, but most bacteria are heterotrophic Domain Archaea Like bacteria, archaea are prokaryotic unicellular organisms that reproduce asexually Archaea do not look that different from bacteria under the microscope, and the extreme conditions under which many species live has made it difficult to culture them Domain Eukarya Eukaryotes are unicellular to multicellular organisms whose cells have a membrane-bounded nucleus Sexual reproduction is common and various types of life cycles are seen Protists, plants, fungi, and animals are all eukaryotic 15-

Figure 15.9 The three-domain system of classification 15-

Connecting the Concepts: Chapter 15 The geologic timescale describes the history of life on Earth The species that are alive today are the end product of all the changes that occurred on Earth as life evolved Every known species that has evolved is given a two-part name consisting of a genus and a specific epithet All sorts of data are used to classify organisms and develop tree diagrams that show evolutionary relationships among species Cladistics is a widely accepted way to determine evolutionary relationships Most biologists today have adopted the three-domain system of classifying species The archaea are structurally similar to bacteria, but their rRNA differs from that of bacteria and is instead similar to that of eukaryotes The domain Eukarya contains four kingdoms: protists, fungi, plants, and animals 15-

Chapt15 Lecture

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Chapt15 Lecture