1. The History of Life Chapter 12

2. Terms O Paleontologists- scientists who study fossils O Fossil record- information about past life, including the structure of the organism, what they ate, what ate them, in what environment they lived, and the order in which they lived. O Extinct- a term used to refer to species that has died out

3. The Fossil Record O The fossil record- information about past life. O The fossil record provides evidence about the history of life on Earth. It also shows how different groups of organisms have changed over time. A mosquito in amber, 35 million years old. (Reproduced by permission of JLM Visuals.)

4. How Fossils Form O Permineralization: occurs when minerals carried by water are deposited around a hard surface. O Natural casts: forms when flowing water removes all of the original bone or tissue, leaving just an impression in sediment

5. How Fossils Form O Trace fossils: record the activity of an organism. Includes nest, burrows, imprints of leaves, and footprints.

6. How Fossils Form O Amber-preserved fossils: organisms that become trapped in tree resin that hardens into amber after the tree gets buried underground. O Preserved remains: forms when an entire organism becomes encased in material such as ice or volcanic ash or immersed in bog.

7. Interpreting Fossil evidence O Radioactive Dating-the age of a sample is calculated based on the amount of remaining radioactive isotopes it contains O Half-life the amount of time it takes for half of the isotope in a sample to decay to a different element. O Not affected by environmental conditions.

8. Half-Life Problems O What is the half-life of a 100.0 g sample of nitrogen-16 that decays to 12.5 g of nitrogen- 16 in 21.6 s? O All isotopes of technetium are radioactive, but they have widely varying half-lives. If an 800.0 g sample of technetium-99 decays to 100.0 g of technetium-99 in 639 000 y, what is its half- life? O A 208 g sample of sodium-24 decays to 13.0 g of sodium-24 within 60.0 h. What is the half- life of this radioactive isotope?

9. Radiometric Dating 1.The technology of radiometric dating provides evidence that the earth is at least 4.6 billion years old. a.Utilizes the natural decay rate of unstable isotopes found in materials to calculate the age of that material. 2.Relative dating- age of a fossil is determined by comparing its placement with that of fossils in other layers of rocks. a.Scientists also use index fossils to compare the relative ages of fossils. 3.Index fossils- used to compare the relative ages of fossils. a.Must be easily recognized and have existed for a short period but have a wide geographic range. b.Will be found in only a few layers of rock.

10. Earth’s Early Atmosphere O Formation of Earth O Most widely accepted hypothesis suggests that the solar system formed by a condensing nebula, a cloud of gas and dust in space. O Sun formed from nebula, debris was pulled together due to gravity and the collisions of debris formed the solar system over millions of years. O Earth's early atmosphere probably contained hydrogen cyanide, carbon dioxide, carbon monoxide, nitrogen, hydrogen sulfide and water O Early Earth was violent and very hot O Asteroids, meteorites, and comets struck releasing heat

11. Earth’s Early History O The First Organic Compounds O Miller and Urey’s experiments suggested how mixtures of the organic compounds necessary for life could have arisen from simpler compounds present on primitive Earth. O Demonstrated that organic compounds could be made by passing an electrical current, to simulate lightning, through a closed system that held a mixture of gases. O Methane, Ammonia, Hydrogen, and Water vapor O They produced a variety of organic compounds such as amino acids O The meteorite hypothesis suggests some amino acids not naturally found on Earth could have come from meteorite or asteroid impacts

12. Earth’s Early History O Early Genetic Material O Evolution of DNA and RNA O Suggested that RNA not DNA may have been used to store genetic material on early Earth. O RNA can copy itself, chop itself into pieces, and from these pieces make even more RNA. O Free Oxygen O The rise of oxygen in the atmosphere drove some forms of life to extinction, while other forms of life evolved new, more efficient metabolic pathways that used oxygen for respiration

13. Cell Structure Hypothesis O Iron-sulfide bubble hypothesis suggests that biological molecules combined in compartments of chimney structures. O The walls of these compartments acted as the first cell membranes. O With the right ingredients the first organic cell membrane could form.

14. Cell Structure Hypothesis O Lipid membrane hypothesis suggests that lipid molecules spontaneously form membrane-enclosed spheres called liposomes. O Can form around organic molecules O Act as membranes that separated organic molecules from the environment O Gives rise to the first true cells

15. Eukaryotic Formation O Microbes O Single-celled organisms changed Earth’s atmosphere by depositing minerals and giving off oxygen as a by-product of photosynthesis O First prokaryotes were anaerobic O Fossil record shows a group of marine cyanobacteria, which carried out photosynthesis O Origin of Eukaryotic Cells O The endosymbiotic theory proposes that eukaryotic cells arose from living communities formed by prokaryotic organisms O Sexual Reproduction and Multicellularity O Asexual vs sexual reproduction O Sexual reproduction leads to genetic diversity, evolution by natural selection and evolution of multicellular life

17. Geologic Time Scale Paleontologists use divisions on the geologic time scale to represent evolutionary time

18. Geologic Time Scale O Geologists divide the time between the Precambrian and the present into three eras- the Paleozoic Era, the Mesozoic Era and Cenozoic Era O Eras are the last ten to hundreds of millions of years and consist of two or more periods. O Periods are the last tens of millions of years, and is associated with a particular rock system. O Epochs are the smallest units of time and last several million years.

19. Precambrian Time O Almost 90% of the Earth’s history occurred during the Precambrian period O Simple anaerobic forms of life appeared. These were followed by photosynthetic forms which added oxygen to the air O Aerobic forms of life, eukaryotes appeared O Some organisms gave rise to multicellular forms which continued to increase in complexity O Few fossils; life existed only in the sea

20. Paleozoic Era “ancient life” O Early in the Paleozoic Era, the fossil record became rich with evidence of many types of marine life (jawless fish, trilobites, arthropods) O Six periods- Cambrian, Ordovician, Silurian, Devonian, Carboniferous and Permian O At the end of the Paleozoic Era there was a mass extinction of both plants and animals on land and sea. As much as 95% of complex life in the oceans disappeared and 70% of land animals O Multicellular animals radiated, first vertebrates evolved and early plants moved onto land

21. Mesozoic Era “middle life” O Events during the Mesozoic Era include the increasing dominance of dinosaurs. The Mesozoic Era is marked by the appearance of flowering plants. O Three periods- Triassic, Jurassic and Cretaceous O At the close of the Cretaceous Period, another mass extinction occurred. More than half of all the plants and animal groups were wiped out, including all of the dinosaurs O First mammals appeared here O Marsupials evolved here

22. Cenozoic Era “recent life” O During the Cenozoic Era, mammals evolved adaptations that allowed them to live in various environments- on land, in water and even in the air O Two periods- Tertiary and Quaternary O During the Quaternary Period the Earth cooled causing a series of ice ages

23. Primate Evolution O Characteristics: O Flexible hands and feet O Forward looking eyes O Enlarged brains O Arms that can rotate in a circle around shoulder joint O Have thumbs that can move against other fingers O Includes: O Lemurs, monkeys, apes, and humans

24. Primate Evolution O Prosimians O Oldest living primate group O Most are small and active at night O Lemurs, lorises, and tarsiers O Tarsiers are called living fossils O Their physical traits have not changed since their appearance in the fossil record 40 million years ago

25. Primate Evolution O Anthropoids O Are humanlike primates O Subdivided into New World monkeys, Old World monkeys, and hominoids O New World monkeys live in trees, have prehensile tails or grasping tails O Old World monkeys spend some time in trees but also forage and travel O Have larger brains O Hominoids are divided into lesser apes (gibbons) and great apes (orangutans, chimps and gorillas) O Walk upright, long lower limbs, opposable thumbs, large brains

26. Extinct Hominids O Homo habilis “Handy man” O Named because of the stone tools found with skeletons O Lived in Kenya and Tanzania O Earliest known hominid to make stone tools O Large brain which resembles modern humans O Homo neanderthalensis “Neanderthal” O Lived in Europe and the Middle East O Believed to have coexisted with Homo sapiens