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Chapter 17 – The History of Life Section 17-1: The Fossil Record.

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1 Chapter 17 – The History of Life Section 17-1: The Fossil Record

2 The fossil record shows how species have changed over time. Paleontologists are scientists who study fossils Fossils can provide insight into where an organism lived, food, predators, and physical structure all of this information = the fossil record

3 The fossil record shows that fossils occur in a certain order and that life has changed More than 99% of all species that have lived on Earth are now extinct

4 Most fossils form in sedimentary rock For a fossil to form, the remains of the organism or some trace has to be preserved

5 The quality of fossil preservation varies; sometimes there are just imprints of soft parts, sometimes hard parts get replaced with long-lasting mineral compounds, and sometimes organisms get buried so quickly they are almost perfectly preserved

6 Once a fossil is discovered, there are several ways a paleontologist can interpret them Many times, they must reconstruct an extinct species so they have to look for similarities & differences between the fossil and living organisms

7 A fossils age is also important and can be determined using 2 techniques; relative dating and radioactive dating

8 Relative dating = when the age of a fossil is determined by comparing its placement with that of fossils in other layers of rock Index fossils can also be used to compare relative age they are easily recognized, only lived during a certain period of time, and were widely distributed With sedimentary rock, older layers are on the bottom and newer layers are on the top

9 Some elements in rocks are radioactive and take a certain amount of time to break down A half-life = the amount of time required for half of the radioactive atoms to decay Radioactive dating = the age of the fossil is calculated based on the amount of remaining radioactive isotopes it contains Carbon-14 is a common isotope used to date fossils

10 The scale was first developed by studying rock layers and index fossils When scientists found major changes in fossil animals and plants they used those times as markers between segments of geologic time Paleontologists use a geological time scale to represent evolutionary time

11 Later, radioactive dating was used to put specific ages to the segments of time and they found that there was not a standard length of time for the segments Geologic time begins with Precambrian time, it is about 88% of Earths History

12 There are currently 3 eras after Precambrian time; Paleozoic Era, Mesozoic Era, and the Cenozoic Era The eras are broken up into smaller time frames called periods After Precambrian time, the basic divisions of the geologic scale are eras and periods

13 Section 17-2: Earths Early History

14 Geologic evidence shows that Earth is about 4.6 billion years old and was not created by one single event Early Earth was much different than the current Earth we know

15 Earths early atmosphere probably contained at least 5 compounds that are no longer part of the atmosphere Earth was also very hot, it was not until about 3.8 billion years ago that Earth was cool enough for oceans to form

16 Scientists now know that their experiments were not accurate, but similar experiments have produced organic compounds 1953 – Miller and Urey tried to figure out how the first beings formed They used the suggested gasses of the early atmosphere and electric sparks for the lightning They were able to produce organic compounds including amino acids

17 Under the right conditions, RNA can help DNA duplicate Some RNA can even grow and duplicate itself One hypothesis is that an RNA based form of life could have led to the DNA control we know now Another unanswered question is which appeared first, RNA or DNA?

18 Earths first atmosphere contained very little oxygen Over time, photosynthetic bacteria became common in shallow seas and started to produce oxygen

19 The oxygen combined with iron in the oceans and caused the oceans to rust The iron fell out and formed bands of iron in Earths crust

20 The rise of oxygen in the atmosphere drove some life forms to extinction, while other life forms evolved new ways to use oxygen for respiration The oxygen also started to accumulate in the atmosphere and replace several other compounds

21 The endosymbiotic theory says that eukaryotic cells formed from a symbiosis among several different prokaryotic organisms About 2 billion years ago, prokaryotic cells began evolving into the ancestor of all eukaryotic cells

22 Prokaryotes that used ATP evolved into mitochondria Other prokaryotes that carried out photosynthesis became chloroplasts Basically, smaller prokaryotes lived inside larger prokaryotes and eventually formed organelles

23 This sped up the evolution process by diversifying organisms they no longer had the exact same DNA as the parent Sometime after eukaryotic cells arose, they began to reproduce sexually

24 Section 17-3: Evolution of Multicellular Life

25 The fossil record indicates that major changes occurred in Earths climate, geography, and life forms

26 Photosynthetic forms then started to add oxygen to the atmosphere Aerobic forms of life appeared and eukaryotes appeared Life existed only in the sea Precambrian time: simple anaerobic forms of life appeared

27 Paleozoic Era: lasted about 300 million years - fossil evidence shows that early in the Paleozoic Era, there was a diversity of marine life.

28 Many of the first known representatives of the animal phyla evolved Ex. Invertebrates, brachiopods, and trilobites Shells and outer skeletons appeared Cambrian Period = Diversification during this period is termed the Cambrian Explosion

29 Some arthropods were the first animals to live on land Some of the first vertebrates and land plants appeared Ordovician/Silurian Periods – ancestors of modern octopi and squids appeared

30 Insects started to appear on land Sharks appeared late in the period Vertebrates began to invade the land – some of the first four-legged vertebrates evolved into the first amphibians Devonian Period – Also called the Age of the Fishes

31 Reptiles evolved from amphibians Winged insects appeared (dragonflies, cockroaches) Plants formed vast swampy areas where eventually the remains formed thick deposits of sediment that changed into coal over time Carboniferous/Permian Periods – life was expanding over Earths continents

32 The mass extinction at the end of the Paleozoic affected both plants and animals on land and in seas as much as 95% of the complex life in the oceans disappeared

33 Mesozoic Era – lasted about 180 millions years and included increasing dominance of dinosaurs and the appearance of flowering plants

34 Triassic Period – those that survived the mass extinction became the main forms of life Important organisms were fishes, insects, reptiles, and cone-bearing plants

35 Sometimes the Mesozoic is called the Age of the Reptiles Some of the first dinosaurs appeared Mammals also appeared late in the period, but were very small

36 Dinosaurs ruled the Earth for about 150 millions years One of the first birds appeared during this time Jurassic Period – dinosaurs became the dominant animals on land

37 Flying reptiles became extinct during this period There were many reptiles in the sea with the fishes Cretaceous Period – reptiles were still the dominant vertebrates New plant life came about; leafy trees, shrubs, and small flowering plants

38 Another mass extinction occurred at the end of the Era – more than half of all plant and animal groups were wiped out, including all of the dinosaurs

39 Cenozoic Era – started about 65 million years ago to present - mammals evolved adaptations that allowed them to live in various environments – on land, in water, and even in the air – also termed the Age of the Mammals

40 Whales and dolphins evolved Grasses evolved Some mammals and birds became very large Tertiary Period – the climate was warm and mild

41 Many of the animals we are familiar with became common Quaternary Period – Earths climate was changing – Earth cooled and went through a series of ice ages About 20,000 years ago, Earths climate began to warm back up

42 The fossil record suggests the early human ancestors appeared about 4.5 million years ago – but they did not look entirely human Homo sapiens may have appeared as early as 200,000 years ago in Africa

43 Section 17-4: Patterns of Evolution

44 Macroevolution refers to large-scale evolutionary patterns and processes that occur over long periods of time. 6 important topics in macroevolution are extinction, adaptive radiation, convergent evolution, coevolution, punctuated equilibrium, and change in developmental genes.

45 Extinction – it usually happens because species compete for resources and environments change Under the changing environment of a mass extinction, extinction isn t related to ordinary natural selection Mass extinctions usually resulted in a burst of evolution afterward that led to the production of many new species.

46 Adaptive Radiation – when a single species or small group of species has evolved, through natural selection and other processes, into diverse forms that live in different ways On a larger scale, examples include dinosaurs, which resulted from adaptive radiation of reptiles Ex. Darwin s finches

47 Convergent evolution – the process by which unrelated organisms come to resemble one another Different types of organisms start off with different raw material for natural selection, but share the same environmental demands like moving though air, moving through water, or eating similar foods

48 Natural selection could mold body structure to fit the environment; ie. arms and legs into wings or flippers Ex. Many aquatic animals have streamlined bodies for swimming through water and have similar looking parts that do not share a common evolutionary history these are analogous structures

49 Coevolution – the process by which two species evolve in response to changes in each other over time

50 Punctuated equilibrium – some species have not evolved much through time, they are in a state of equilibrium Sometimes something happens to upset the equilibrium and a change occurs Many new species are produced by periods of rapid change when the equilibrium is upset

51 The rapid change can be caused by small populations becoming separated from the main part or even when a small population migrates to a new environment Punctuated equilibrium describes the pattern of long, stable periods interrupted by brief periods of more rapid change

52 Developmental genes and body plans – changes in genes for growth can produce differentiation during embryological development and can produce transformations in body shape and size Small changes in control genes can produce large changes in adult animals

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