Ch 25: History of life …as we understand it

1. Ch 25: History of life …as we understand it • Conditions on early Earth made the origin of life possible • Chemical and physical processes on early Earth may have produced very simple cells through a sequence of stages: • Abiotic synthesis of small organic molecules • Joining of these small molecules into macromolecules • Packaging of molecules into protocells • Membraneous packets of chemicals

2. Synthesis of Organic Compounds… • Earth formed about 4.6 billion years ago, along with the rest of the solar system • Bombardment of Earth by rocks and ice likely vaporized water and prevented seas from forming before 4.2 to 3.9 billion years ago • Earth’s early atmosphere likely contained water vapor and chemicals released by volcanic eruptions (nitrogen, nitrogen oxides, carbon dioxide, methane, ammonia, hydrogen, hydrogen sulfide)

3. Are the key building blocks of life hard to come by? • Amino acids have been found in meteorites • RNA monomers have been produced spontaneously from simple molecules • In water, lipids and other organic molecules can spontaneously form vesicles with a lipid bilayer • Adding clay can increase the rate of vesicle formation • Vesicles exhibit simple reproduction and metabolism and maintain an internal chemical environment • Resultprotocells

4. Present The fossil record documents this history of life in geologic time Dimetrodon Rhomaleosaurus victor 100 mya 1 m 175 Tiktaalik 0.5 m 200 270 300 4.5 cm Hallucigenia Coccosteus cuspidatus 375 400 1 cm Dickinsonia costata 500 525 2.5 cm Stromatolites 565 600 1,500 Fossilized stromatolite 3,500 Tappania Figure 25.4

5. How Rocks and Fossils Are Dated • Sedimentary strata reveal the relative ages of fossils • The absolute ages of fossils can be determined by radiometric dating • A “parent” isotope decays to a “daughter” isotope at a constant rate • Each isotope has a known half-life, the time required for half the parent isotope to decay Refer to: Keeping Time handout

6. Limitations of Carbon dating • Radiocarbon dating can be used to date fossils up to 75,000 years old • For older fossils, some isotopes can be used to date sedimentary rock layers above and below the fossil

7. Geologic record is divided into the Archaean, the Proterozoic, and the Phanerozoic eons The Phanerozoic encompasses multicellular eukaryotic life and is divided into three eras: Paleozoic, Mesozoic, and Cenozoic The Cambrian explosion refers to the sudden appearance of a multitude of modern body designs (530 million years ago) first evidence of predator-prey interactions

8. Appearance of selected animal groups in the fossil record Sponges Cnidarians And, the colonization of land… Fungi, plants, and animals began to colonize land about 500 million years ago Vascular tissue in plants transports materials internally and appeared by about 420 million years ago Plants and fungi today form mutually beneficial associations and likely colonized land together Arthropods and tetrapods are the most widespread and diverse land animals Tetrapods evolved from lobe-finned fishes around 365 million years ago Echinoderms Chordates Brachiopods Annelids Molluscs Arthropods PROTEROZOIC PALEOZOIC Ediacaran Cambrian 635 605 575 545 515 485 0 Time (millions of years ago) Figure 25.10

9. The fossil record shows that most species that have ever lived are now extinct… Further reading: the last parts of Ch 25 that includes Mass extinctions

10. What is meant by phylogeny? Evolutionary history of a species… Based on common ancestry Supported by shared characteristics and genetics Documented by fossils and genetics Ch 26: Phylogeny and Systematics Eon > Era > Periods > Epochs

11. Systematics? = study of the organismal diversity of life How do we make sense of all this diversity? Organize it… using fossil, molecular, and genetic data to infer evolutionary relationships Taxonomy & classification

12. Taxonomy is the ordered division and naming of organisms Domain Kingdom Phylum Class Order Family Genus Species Each group is nested within the level above Broad or less specific More specific Phylogenies show evolutionaryrelationships --Diversity of Life

13. Closely related species belong to the same genus, similar genera are included in a family, etc…Species that share the same structures, behaviors, etc, can interbreed and produce fertile offspring.

14. Grouped by shared characters (Evolutionary relationships) Embryology Reproduction strategies Symmetry (body plan) Morphology Feeding mode Interspecific interactions (e.g. symbiosis) Etc… Systematists depict evolutionary relationships in branching phylogenetic trees

15. Branch point: where lineages diverge Taxon A Taxon B Sister taxa • A phylogenetic tree represents a hypothesis about evolutionary relationships • Each branch point represents the divergence of two species • Sister taxaare groups that share an immediate common ancestor Taxon C Taxon D Taxon E ANCESTRAL LINEAGE Taxon F Basal taxon Taxon G This branch point forms a polytomy: an unresolved pattern of divergence. This branch point represents the common ancestor of taxa A–G.

16. Cladistics groups organisms by common descent • A clade is a group of species that includes an ancestral species and all its descendants • Clades can be nested in larger clades, but not all groupings of organisms qualify as clades

17. Figure 26.11 Lancelet (outgroup) TAXA Lancelet (outgroup) Lamprey Lamprey Leopard Turtle Bass Frog Vertebral column (backbone) Bass 0 1 1 1 1 1 Vertebral column Hinged jaws 0 0 1 1 1 1 Frog Hinged jaws Four walking legs 0 0 0 1 1 CHARACTERS 1 Turtle Four walking legs 0 0 0 0 1 1 Amnion Amnion Leopard Hair 0 0 0 0 1 0 Hair (b) Phylogenetic tree (a) Character table

18. Historical 5 Kingdom system… until about 1970

19. 3 domains, many kingdoms