Chapter 17: The History of Life

1. Chapter 17: The History of Life

2. 17.1 The Fossil Record • Paleontologist: scientist who studies fossils • Fossil: preserved remains or evidence of an ancient organism • Extinct: term used to refer to a species that has died out • Key Concept: The fossil record provides evidence about the history of life on Earth. It also shows how different groups of organisms, including species, have changed over time.

3. 17.1 Interpreting Fossil Evidence • Relative dating: age of a fossil is determined by comparing its placement with that of fossils in other layers of rock • Index Fossils: distinct fossils found in certain layers of rock in a wide geographic range (Fig. 17-3) • Key Concept: Relative dating allows paleontologists to estimate a fossil’s age compared with that of other fossils.

4. 17-1 Radioactive Dating • Scientists use half-lives of radioactive elements to determine the age of a sample. • Half-life: length of time required for half of the radioactive atoms in a sample to decay (Fig. 17-4) • Key Concept: In radioactive dating, scientists calculate the age of a sample based on the amount of remaining radioactive isotopes it contains

5. 17.2 Earth’s Early History

6. 17.2 Formation of Earth • Estimated age of the earth based on geological evidence: 4.6 billion years • Key Concept: Earth’s early atmosphere probably contained hydrogen cyanide, carbon dioxide, carbon monoxide, nitrogen, hydrogen sulfide, and water.

7. 17.2 The First Organic Molecules • Two scientists created conditions of the early Earth in the lab. After a few days, several amino acids formed. (Fig. 17-8) • Key Concept: Miller and Urey’s experiments suggested how mixtures of the organic compounds necessary for life could have arisen from simpler compounds present on a primitive Earth. “Scientists now know that Miller and Urey’s original simulations of Earth’s early atmosphere were not accurate.” (p. 424)

8. 17.2 Free Oxygen • Early life forms were anaerobic because they lived in an oxygen-free environment. • Key Concept: The rise of oxygen in the atmosphere drove some life-forms to extinction, while other life-forms evolved new, more efficient metabolic pathways that used oxygen for respiration.

9. 17.2 Origin of Eukaryotic Cells • Endosymbiotic theory: eukaryotes formed from the symbiotic (interdependent) relationship between ancestral eukaryotes and aerobic or photosynthetic bacteria. (Fig. 17-12) • Key Concept: The endosymbiotic theory proposes that eukaryotic cells arose from living communities formed by prokaryotic organisms. • Evidence: Similarities between mitochondria, chloroplasts and bacteria. (DNA, ribosomes and binary fission)

10. SKIPPED17.3 Evolution of Multicellular Life

11. Bio Warm-Up: Cinco de Mayo!!! • ACHOO Syndrome is a dominant disorder which causes people to sneeze uncontrollably in response to a stimulus such as looking at bright lights. In a population of 21,000 students at Monsters University, 5250 students were found to not have ACHOO Syndrome. What is the frequency of the recessive allele at MU? How many heterozygous students attend MU? How many homozygous dominant students? p + q = 1 p2 + 2pq + q2 = 1 Given: Possible genotypes: AA AaaaA = p a = q Students without disorder: aa = 5250/21000 = 0.25 = q2 Frequency of recessive allele: Sqrt(q2) = sqrt(0.25)  q = 0.5 p + q = 1  p = 1 – q  p = 1 – 0.5 = 0.5 # of AA individuals: p2 = (0.5)2 = 0.25 x 21000 = 5250 students # of Aa individuals: 2pq = 2(0.5)(0.5) = 0.5 = 10500 students

12. Bio Warm-Up: Cinco de Mayo!!! • There are 150 dominant alleles in the gene pool of a population of 500 individuals. Calculate the relative frequency of the dominant allele. • Relative Frequency = # of alleles/total number of alleles • RF = 150/1000 (2 alleles per individual) = 0.15 or 15% • List two methods a paleontologist would use to date a fossil. • Relative dating: fossil record and layers of rock • Radioactive dating: measuring amount of isotopes in fossil

13. 17.4 Patterns of Evolution

14. 17.3 Patterns of Evolution • Macroevolution: large-scale evolutionary patterns and processes that occur over long periods of time. • Six Topics: • Extinction: mass extinctions opened ecological opportunities for surviving organisms. (i.e. dinosaurs replaced by mammals and birds) • Adaptive radiation: many species evolving from a single or small group of species (Fig. 17-22) • Convergent evolution: different species from similar climates resemble each other (Fig. 17-23)

15. 17.3 Patterns of Evolution • Macroevolution: large-scale evolutionary patterns and processes that occur over long periods of time. • Six Topics: (Skipped topic 6) • Coevolution: organisms closely connected by ecological interactions evolve together (Fig. 17-24) • Punctuated equilibrium: stable periods and rapid periods of evolution (Fig. 17-25) • Changes in developmental genes: expression of hox genes greatly effects development. (17-26)

16. Biology Warm-Up May 6, 2014 • Describe and sketch a picture of the endosymbiotic theory. See figure 17.12 in your textbooks. Endosymbiotic theory explains how modern plants/animals have risen from ancient prokaryotic ancestors. As oxygen levels began to rise in Earth’s early atmosphere, ancient anaerobic cells formed symbiotic relationships with aerobic prokaryotes which they engulfed. The prokaryotes eventually evolved into modern day mitochondria or photosynthetic prokaryotes evolved into modern day chloroplasts. These symbiotic relationships allowed for the evolution of aerobic eukaryotic cells. • List the 5 topics of macroevolution discussed in class. • Extinction (i.e. mass extinction of dinosaurs made way for mammals) • Adaptive radiation (i.e. Darwin’s finches; tree of life) • Convergent evolution (i.e. similar morphology of shark, penguin and dolphin) • Coevolution (i.e. change to orchid causes change in moth) • Punctuated equilibrium (i.e. periods of stable, gradual change interrupted by fast paced evolution)