1. The History of Life Chapter 12

2. Fossils and Ancient Life A fossil is the preserved remains or evidence of an ancient organism Scientists who study fossils are paleontologists The fossil record is the grouping of similar organisms from oldest to most recent It can provide evidence about the history of life on Earth and show how different groups of organisms have changed over time

3. Extant v/s Extinct More than 99 percent of all species that have ever lived on Earth have become extinct The term extinct is used to describe a species that no longer has a living representative The term extant is used to describe a species that has living representatives

4. The Formation of Fossils A fossil can be as large and complete as an entire, perfectly preserved animal, or as small as a tiny fragment of a jawbone or leaf For a fossil to form, either the remains of the organism or some trace of its presence must be preserved The formation of any fossil depends on a precise combination of conditions Because of this, the fossil record provides an incomplete record of the history of life – for every organism that leaves a fossil, many more die without leaving a trace

5. Section 17-1 Figure 17-2 Formation of a Fossil Go to Section: The Formation of Fossils

6. Relative Dating of Fossils Sedimentary strata reveal the relative ages of fossils: In relative dating, the order of rock strata is used to determine the relative age of fossils. Older fossils are found in deeper layers of strata, and younger fossils are found in superficial layers of strata.

7. Radioactive Dating of Fossils Radioactive dating is the use of half-lives to determine the age of a sample Radioactive elements decay, or break down, into non-radioactive elements at a steady rate called a half-life A half life is the length of time required for half of the radioactive atoms in a sample to decay In radioactive dating, scientists calculate the age of a sample based on the amount of remaining radioactive isotopes it contains

8. Formation of Earth Earth’s early atmosphere probably contained hydrogen cyanide, carbon dioxide, carbon monoxide, nitrogen, hydrogen sulfide, and water About 4 billion years ago, Earth cooled enough to allow the first solid rocks to form on its surface About 3.8 billion years ago, Earth’s surface cooled enough to allow water to remain liquid Could organic molecules evolve under these conditions?

9. Mixture of gases simulating atmospheres of early Earth Spark simulating lightning storms Condensation chamber Cold water cools chamber, causing droplets to form Water vapor Liquid containing amino acids and other organic compounds Section 17-2 The First Organic Molecules http://bcs.whfreeman.com/thelifewire/content/chp03/0301s.swf Go to Section: 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. Miller and Urey produced amino acids, which are needed to make proteins, by passing sparks through a mixture of hydrogen, methane, ammonia, and water.

10. Aerobic bacteria Ancient Prokaryotes Ancient Anaerobic Prokaryote Primitive Aerobic Eukaryote Primitive Photosynthetic Eukaryote Chloroplast Photosynthetic bacteria Nuclear envelope evolving Mitochondrion Plants and plantlike protists Animals, fungi, and non-plantlike protists Origin of Eukaryotic Cells http://www.sumanasinc.com/webcontent/animations/content/organelles.html Go to Section: The endosymbiotic theory, championed by Lynn Margulis, proposes that eukaryotic cells arose from living communities formed by prokaryotic organisms

11. Patterns of Macroevolution Macroevolution refers to the large scale evolutionary changes that take place over long periods of time Six important patterns of macroevolution are: 1. Mass extinctions 2. Adaptive radiation 3. Convergent evolution 4. Coevolution 5. Divergent evolution 6. Punctuated equilibrium

12. Mass Extinctions Extinctions occur all the time More than 99% of all species that ever lived are extinct today Usually, extinctions occur at a constant rate Several times, however, huge numbers of species have disappeared in mass extinctions Paleontologists think that most mass extinctions in the past were caused by multiple factors Asteroids Volcanic activity Changing position of continents Changing sea levels

13. Adaptive Radiation  Adaptive radiation is the RAPID evolution of a group of organisms following some large-scale disturbance.  Adaptive radiation typically occurs when a few organisms make their way to new, often distant areas or when environmental changes cause numerous extinctions, opening up ecological niches for the survivors.  Fossil evidence indicates that mammals underwent a dramatic adaptive radiation after the mass extinctions of dinosaurs 65 million years ago.

14. Adaptive Radiation in Darwin’s Finches

15. Convergent Evolution Convergent evolution describes 2 unrelated species that share similar traits. These similarities are not due to common ancestry, but rather a result of similar environmental factors (creates analogous structures).

16. Coevolution  Coevolution describes the evolution of one species in response to new adaptations that appear in another species of which the first shares close interaction.

17. Divergent Evolution  Divergent evolution is the accumulation of differences between groups which can lead to the formation of new species.  It is usually a result of diffusion of the same species to different and isolated environments which blocks the gene flow among the distinct populations.  These barriers to gene flow allow differentiated fixation of characteristics through genetic drift and natural selection.

18. Patterns of Evolution

19. Punctuated Equilibrium Punctuated equilibrium is a pattern of evolution in which long stable periods (gradualism) are interrupted by brief periods of more rapid change Typically occurs when new niches become available following a mass extinction

20. Gradualism v/s Punctuated Equilibrium Species descended from a common ancestor gradually diverge more and more in morphology as they acquire unique adaptations. A new species changes most as it buds from a parent species, and then changes little for the rest of its existence.

21. Section 17-4 that are can undergo inunder formin Species Unrelated Related Inter- relationshiops Similar environments Intense environmental pressure Small populations Different environments Coevolution Convergent evolution Extinction Punctuated equilibrium Adaptive radiation Go to Section: Patterns of Macroevolution