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Chapter 17 – The History of Life

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

2 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 The fossil record shows how species have changed over time.

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

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 relative dating and radioactive dating
A fossil’s 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 With sedimentary rock, older layers are on the bottom and newer layers are on the top 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

9 Radioactive dating = the age of the fossil is calculated based on the amount of remaining radioactive isotopes it contains 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 Carbon-14 is a common isotope used to date fossils

10 Paleontologists use a geological time scale to represent evolutionary time
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

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 Earth’s History

12 After Precambrian time, the basic divisions of the geologic scale are eras and periods
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

13 Section 17-2: Earth’s Early History

14 Geologic evidence shows that Earth is about 4
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 Earth’s 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 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 Scientists now know that their experiments were not accurate, but similar experiments have produced organic compounds

17 Another unanswered question is which appeared first, RNA or DNA?
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

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

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

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

24 Evolution of Multicellular Life
Section 17-3: Evolution of Multicellular Life

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

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

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

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

30 Devonian Period – Also called the “Age of the Fishes”
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

31 Carboniferous/Permian Periods – life was expanding over Earth’s continents
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

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

37 Cretaceous Period – reptiles were still the dominant vertebrates
Flying reptiles became extinct during this period There were many reptiles in the sea with the fishes 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 Tertiary Period – the climate was warm and mild
Whales and dolphins evolved Grasses evolved Some mammals and birds became very large

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

42 The fossil record suggests the early human ancestors appeared about 4
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 Ex. Darwin’s finches On a larger scale, examples include dinosaurs, which resulted from adaptive radiation of reptiles

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
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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