Life’s Origin and Early Evolution Chapter 20

20.1 In the Beginning . . . Knowledge of modern ___________________ and ___________________ are the basis for scientific ___________________ about early events in Earth’s history

Ongoing Star Formation The Eagle ______________, photographed by the Hubble space telescope

Early Earth

Stanley Miller’s Experiments

20.2 How Did Cells Emerge? We will never know for sure how the first ___________________ came to be, but we can investigate the possible steps on the road to ___________________

Possible Origins of Complex Organic Compounds Clay templates on _________________ flats; iron-sulfide rocks at hydrothermal vents on the ___________________ floor

Models for Protocells _______________________________ vesicles and ___________________ -coated clay

formation of protein–RNA systems, evolution of DNA living cells membrane-bound proto cells self-replicating system enclosed in a selectively permeable, protective lipid sphere enzymes and other proteins DNA RNA formation of protein–RNA systems, evolution of DNA formation of lipid spheres Figure 20.6 Laboratory-formed models for protocells that may have preceded the emergence of cells. (a) Selectively permeable vesicles with an outer membrane of proteins were formed by heating amino acids, then wetting the resulting protein chains. (b) RNA-coated clay (stained red) enclosed in a simple membrane composed of fatty acids and alcohols (green). Mineral-rich clay promotes the assembly of such vesicle-like forms and catalyzes the formation of RNA strands from free nucleotides. (c) One hypothesis for steps that led from lifeless chemicals to living cells. spontaneous formation of lipids, carbohydrates, amino acids, proteins, nucleotides under abiotic conditions Fig. 20-6c, p. 321

Fossil Prokaryotic Cells

The Rise of Eukaryotes Oldest eukaryotic fossils: __________________ years

Origins of Nucleus, ER, and Golgi Body The ___________________ and ____________ may have arisen through modification of infoldings of ___________________

Evidence of Endosymbiosis

20.5 Time Line for Life’s Origin and Evolution

Lessons of Chile’s Atacama Desert What we learn about life on Earth informs our ideas about the possibility of life ___________________

Major Events in the History of Life