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

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)

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

The fossil record documents this history of life in geologic time Dimetrodon Stromatolites Fossilized stromatolite Coccosteus cuspidatus 4.5 cm 0.5 m 2.5 cm Present Rhomaleosaurus victor Tiktaalik Hallucigenia Dickinsonia costata Tappania 1 cm 1 m 100 mya ,500 3, Figure 25.4

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

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

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

Appearance of selected animal groups in the fossil record 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 Sponges Cnidarians Echinoderms Chordates Brachiopods Annelids Molluscs Arthropods Ediacaran Cambrian PROTEROZOICPALEOZOIC Time (millions of years ago) Figure 25.10

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

Ch 26: Phylogeny and Systematics 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 Eon > Era > Periods > Epochs

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

Phylogenies show evolutionaryrelationships --Diversity of Life 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

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.

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

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

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

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

Historical 5 Kingdom system… until about 1970

3 domains, many kingdoms