Geologic Time and Phylogeny (Chapter 26) Evolutionary history...

Phylogeny and Systematics Phylogeny: The evolutionary history of a species or group of related species Like an evolution family tree: Systematics: the study of biological diversity in an evolutionary context grouping organisms and seeing how organisms are related due to evolution

How do scientists create a phylogeny? Fossils: the preserved remnants or impressions left by organisms that lived in the past.

How do scientists know the age of a fossil? Relative Dating New layers form on top of old ones When a dead organism is trapped in sediment, this fossil is frozen in time relative to other strata (layers) in a local sample

Absolute Dating Radiometric dating is the method used most often to determine absolute ages for fossils. organisms accumulate radioactive isotopes when they are alive, but concentrations of these isotopes decline after they die. These isotopes undergo radioactive decay… one element is transformed to another element. An isotope’s half-life, the time it takes for 50% of the original sample to decay, unaffected by temperature, pressure, or other variables.

Carbon-14 The radioactive isotope, carbon-14, is present in living organisms. Organism dies: carbon-14 decays to nitrogen-14 The half-life of carbon-14 is 5,730 years It is possible to determine the age of a sample by examining how much C14 has decayed.

Uranium- 238 Elements with longer half-lives are used to date older fossils. While uranium-238 (half life of 4.5 billion years) is not present in living organisms to any significant level, it is present in volcanic rock. If a fossil is found sandwiched between two layers of volcanic rock, we can deduce that the organism lived in the period between the dates in which each layer of volcanic rock formed.

Relative vs. Absolute Dating

Geologic Time Scale Geologists have established a geologic time scale with a consistent sequence of historical periods. These periods are grouped into four eras: the Precambrian, Paleozoic, Mesozoic, and Cenozoic eras. Boundaries between geologic eras and periods correspond to times of great change, especially mass extinctions, not to periods of similar length.

Mass Extinctions

Mass Extinctions

Plate Tectonics

Plate Tectonics

Phylogeny and Systematics Organizing evolution!

Intro The goal - to reconstruct the history of life on earth. The method – Systematics is the study of biological diversity in an evolutionary context. The result: The development of phylogeny, the evolutionary history of a species or group of related species.

Classification Taxonomy: Naming and classification of species and groups of species Scientists use hierarchical classification of species into broader and broader groups

Example How would you classify a Toyota 4Runner? Transportation Car SUV Toyota 4Runner

Try this! Organize the taxa. Start with the smallest group at the bottom and work your way up to largest group at the top. Next match the scientific names for the cheetah with the correct taxa.

Phylogeny and Cladograms Phylogeny: The evolutionary history a species or group of species Cladogram: phylogenetic diagram based on cladistics Each branch point represents the divergence of two species from a common ancestor

Connection between classification and phylogeny…

Now try this! Imagine you are a scientist studying insects in the rainforest of Bolivia. You’ve found six insects that look like they are related. Based on shared derived characteristics construct a cladogram and character table.