Chapter 17: The History of Life

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.

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.

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

17.2 Earth’s Early History

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.

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)

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.

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)

SKIPPED17.3 Evolution of Multicellular Life

Bio Warm-Up: Cinco de Mayo!!!1. 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 = 1Given: Possible genotypes: AA Aa aa A = p

a = qStudents without disorder: aa = 5250/21000 = 0.25 = q2 Frequency of recessive allele: Sqrt(q2) = sqrt(0.25) q = 0.5p + 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

Bio Warm-Up: Cinco de Mayo!!!2. 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%

3. 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

17.4 Patterns of Evolution

17.3 Patterns of Evolution• Macroevolution: large-scale

evolutionary patterns and processes that occur over long periods of time.• Six Topics: 1. Extinction: mass extinctions opened

ecological opportunities for surviving organisms. (i.e. dinosaurs replaced by mammals and birds)

2. Adaptive radiation: many species evolving from a single or small group of species (Fig. 17-22)

3. Convergent evolution: different species from similar climates resemble each other (Fig. 17-23)

17.3 Patterns of Evolution• Macroevolution: large-scale

evolutionary patterns and processes that occur over long periods of time.• Six Topics: (Skipped topic 6)4. Coevolution: organisms closely connected

by ecological interactions evolve together (Fig. 17-24)

5. Punctuated equilibrium: stable periods and rapid periods of evolution (Fig. 17-25)

6. Changes in developmental genes: expression of hox genes greatly effects development. (17-26)

Biology Warm-Up May 6, 2014 1. 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.

2. 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)