Chapter 26: Early Earth

THE HISTORY OF LIFE ON EARTHEvidence #3: The Fossil Record1How are fossils discovered and dated?Answer: Fossils are found in many locations and dated using radioactivity and through the location of index fossils2Fossil Formation & the History of Life

3Carbon dating after an organism dies it stops accumulating carbon. Since C14 exists in nature scientists can determine the age of the fossil by measuring the ratio of carbon 14 to nitrogen 14 or to carbon 12. However, this is accurate only up to 75,000 yrs. Carbon has a half-life of 5,730 years

The Earths magnetic field varies throughout time. Iron-rich particles will line up and point to the Earths magnetic pole. The alignment of these particles will then be frozen in time

Other isotopes and methods that are used that include the following:1. Fossils that are trapped in volcanic rocks are determined by measuring the amount of potassium-40 to argon-40 levels. K40 decays to argon which is trapped in the rock. This is very useful because each volcanic eruption will reset the K40 clock to 0 since argon is emitted during the eruption. This allows scientists to estimate the date of the fossil

2. Scientists also look at the levels of magnetism which get frozen in time since Earths magnetic field varies

3. They also measure the amount of potassium-40 in sedimentary rock layers. Potassium-40 has a half-life of 1.3 billion years. Scientists will take the dates of the strata above and below the fossil which gives them an estimate of the time that the fossil formed

4. Uranium has a half-life of 4.5 billion yearsSedimentary Rock Strata (layers)

The younger layers overlay the older layers. Scientists can compare similar strata across the world and perform a comparative dating analysis based on the fossils that are above and below in the surrounding strata4Types of Fossils

5In order to determine phylogenetic data it is important to study the fossil record even though there are gaps. BonesSkull bonesPetrified wood forms as minerals seep inScorpion preserved in amberLeaf imprint sometimes whole leaves are preserved and organic material can be extractedshell

6Mammoth skeleton

Wooly Mammoths are fossils from the ice age about 200,000 years ago. It went extinct around 10,000 years ago, but one population survived until about 4,000 years ago. It is speculated to be the behemoth from the bible. It lived across parts of Asia, Europe and the northern part of North America

It is a distant relative of the mastodon which existed around 25 mya

Its height ranges from 9-11 ft and it weighs around 6 tons

7Frozen Baby MammothCloning Ancient Mammoths

The mammoth was found in Siberia8Index Fossils and the Geologic RecordIndex fossil fossil used to define a specific geologic time periodOrganisms best used for index fossils are short-lived; occurred on Earth for only a few thousand yearsIndex fossils are: common, easy to identify and have a widespread distributionExamples: trilobites, ammonites and brachiopods9

Trilobite Fossils: Paleozoic Era (526 mya 250 mya)11Brachiopod

Brachiopods weremost abundantduring the Paleozoic period,but still existtoday12Ammonite Fossil: Devonian Cretaceous Period

13What Do Scientists Learn From the Fossil Record?14Evidence from Studying the Fossil RecordOrder of appearance of the fossils mimics the tree of life in complexityLarge spans of geologic time ended in mass extinctions & that these extinctions were followed by an increase in the diversity of other organismsDiscovery of transitional fossils that clearly show characteristics of two distinct species

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Order of Fossil AppearanceProkaryotes precede eukaryotes

Fish amphibians reptiles birds mammals17

Additional ObservationsAs the layers of rock changed, old species disappeared and new species appeared99% of species are now extinctConclusions: life became more complex through timespecies unable to adapt went extinct18

Stromatolites (first prokaryotic fossils) layered rocks that form when ancient prokaryotes bind sediment together; 3.5 million yrs ago (3.5 mya)

Stramatolite Beds

CyanobacteriaCyanobacteria photosynthetic prokaryotes; were the first organisms to carry out photosynthesis

Origin of Eukaryotic Life

Origin of first eukaryotic life: 2.1 byaOrigin of first multicellular eukaryotic fossil: alga; 1.2 bya

Colonization of Land500 million years agoMacroscopic plants, fungi & animalsOccurred during Paleozoic periodPlants colonized jointly with fungi; today several plants have symbiotic relationships with fungi for the functioning of their rootsPlants paved the way for herbivores; herbivores then paved the way for predatorsFig. 25-14

Total extinction rate(families per million years):Time (millions of years ago)Number of families: CenozoicMesozoicPaleozoicEOSDCPTrJ5420488444416359299251200145EraPeriod5CPN65.500200100300400500600700800151020Geologic Time & Mass Extinctions25Figure 25.14 Mass extinction and the diversity of life

Fig. 25-1Cretaceous Extinction26Figure 25.1 What does fossil evidence say about where these dinosaurs lived?

Fig. 25-15

NORTHAMERICAChicxulubcraterYucatnPeninsulaBye, Bye Dinosaurs!27Figure 25.15 Trauma for Earth and its Cretaceous lifeFor the Discovery Video Mass Extinctions, go to Animation and Video Files.

Very late cynodont (195 mya)Later cynodont (220 mya)Early cynodont (260 mya)Therapsid (280 mya)Synapsid (300 mya)TemporalfenestraTemporalfenestraTemporalfenestraEARLYTETRAPODSArticularKeyQuadrateDentarySquamosalReptiles(includingdinosaurs and birds)DimetrodonVery late cynodontsMammalsSynapsidsTherapsidsEarlier cynodontsHello Mammals!28Figure 25.6 The origin of mammals

Transitional FossilsTransitional fossils are often referred to as the missing link that connects two different types of animals Transitional fossils are fossils that combine the features of two types of animals; these fossils DO NOT have to be the ancestor of all modern forms or a 50/50 intermediateExample: a transitional fossil between dinosaurs & birds only needs to have a combination of traits found only in birds and traits found only in dinosaurs

30The First Transitional Fossil DiscoveryFeathered Dinosaurs: the Link between dinosaurs and birds31

Archaeopterx

Was discovered in 1860 by Thomas Huxley and was believed to be the transitional fossil between birds and dinosaursIt was initially thought that this was the first bird, but now is believed to be another feathered dinosaur. It lived around 148 mya.

Bird-like features: feathers and an opposable big toeReptile-like features: long, bony tail (birds dont have the bones in the tail feathers, jaws and teeth

32Mutant Chicken Embryo with Teeth

Discovered in the lab of Matthew Harris the teeth are similar to the teeth of an alligator

It is the result of a recessive lethal trait called talpid

These findings have been repeated in normal chicken embryos. If normal chicken embryos are infected with a virus that mimics the molecular signal given by the mutation they will briefly grow teeth that are resorbed by the embryo later in development.

This discovery was made around 4/9/13

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Caudipterx Fossil34The Discovery of Feathered Dinosaurs35The newly discovered feathered dinosaur Anchiornis huxleyi, is the oldest known bird-like dinosaur. Its size is 28 cm and it is approximately 121 million years old. Similar fossils of this animal where also found in China

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The 130 million year old Tianyulong confuciusi from China is about 0.7 m long and displays 3 distinct patches of featherlike structures. 37

Microraptor GuiFossil was found in China and published in the journal Nature in January of 2003. The dinosaur had feathers creating front and hind wings. The position of the feathers more toward the end of the limb also mimics the positioning of a birds feathers.

Importance of this feathered dinosaur is that this is the only known dinosaur that has asymmetrical feathers. These types of feathers are the only ones that would be useful for flight. Only birds had been known to have asymmetrical feathers prior to this find.38

Bi-plane flyer: New research on Microraptor gui suggests that the flying reptile from 125 million years ago may have utilitized the same aerodynamics as a biplane.39A Living Transitional FossilVelvet Worms: the Link between annelids and arthropods40Annelids and Mollusks

Velvet Worm CharacteristicsAnnelid CharacteristicsSoft-bodiedRespiration: through diffusion; requires damp and humid habitatsParapodia-like appendagesArthropod CharacteristicsHas an exoskeleton of chitin and undergoes moltingSegmentation with two appendages per segmentOpen circulatory system

How did fins become feet?Transitional fossil between water and land Proposed HypothesesTetrapods includes everything with 4 limbsAcanthostega had limbs, but couldnt walk on land; still had gills & tail fins but still breathe air; 365 myaTiktaalik rosae found recently; called land fish; fin-like appendages and lungs; 375 mya44Scientific American December 2005Discover July 2006

AcnathostegaTetrapod that lived in Greenland 365mya

45Tikaatilik roseae

Found on Ellesmere Island: Canadian provinceFish-like features: gills, scales and finsAmphibian-like features: flattened head, eyes and nostrils on top instead of on the sides and its has a neckTwo important features: ribs so it could use lungs to breathe oxygen*The number of bones it had and the position of those bones is similar to us46

Evolution from Land to Sea47A Whale of a TaleThe Journey Back to the Ocean48Transitional Whale FossilWhales fossils were discovered in Egypt & Pakistan that contained hind limbs

In modern whales about 1/500 whales are born with a rear leg

49Transition from Land Back to Sea: The Evolution of WhalesWhy go back to the sea?

One Theory: Disappearance of predatory marine dinosaurs

First Transitional fossil in the journey: prehistoric hippo-like animal called Indohyus50

IndohyusThis creature has ears and teeth that are only found in whalesFossil evidence shows that it spent part of its life in water51

PakicetusAmbulocetus52

53Modern Day Transitional Whale Organism: Hippo???

Hippos mate in water and their babies learn to swim before they learn to walkThe babies nurse underwater

Hippos also secrete a pinkish substance that functions as a sunscreen because their skin is very susceptible to damage from the sun54

55Evidence # 4: Biogeography56

Flightless Cormorant: How did it get to the Galapagos?Was there an ancestral bird of the cormorants that was able to fly?57BiogeographyDefinition the past & present geographic distribution of species

What biogeography revealed to scientists:Species will resemble other species more closely in the same geographic region, then species that live in similar habitats with similar adaptations

58Island BiogeographyIsland biogeography shows that species on islands resemble species from the nearest mainland more closely than species on islands with similar environments

Example: Galapagos Islands: animals on the Galapagos Islands resemble the animals on the South American coast more than similar animals in other climates

59Important Biogeography Discovery: Australian MarsupialsCurrent Biogeography: LIVING marsupials are found primarily on the Australian continent with fewer species in Central and South America and one in North America, the Virginia OpossumPast Biogeography: FOSSIL marsupials are found in Australia, North America, South America and Antarctica

1 sugar glider2 flying squirrel3 tasmanian wolf4 wolf5 cuscus6 loris

7 numbat8 anteater9 marsupial mouse10 mouse

11 potoroo12 springhare 13 marsupial mole14 mole

15 wombat16 groundhog17 thylacosmilus18 saber-tooth cat

19 shrew opossum20 shrew

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Marsupial Lion64

Marsupial lion fossil65What Can Explain the Distribution of Modern Marsupials & Fossil MarsupialsAnswer: Plate Tectonics66Continental Drift and the Breakup of Pangea Earths crust is broken into a series of plates that are constantly shiftingSeveral times during Earths geologic history these plates have combined together to form supercontinents and then broken apart againScientists believe that the next supercontinent will occur 250 million years from now67Fig. 25-12b Major continental plates

PacificPlateNazcaPlateJuan de FucaPlateCocos PlateCaribbeanPlateArabianPlateAfricanPlateScotia PlateNorthAmericanPlateSouthAmericanPlateAntarcticPlateAustralianPlatePhilippinePlateIndianPlateEurasian Plate68Figure 25.12 Earth and its continental platesFig. 25-13

SouthAmericaPangaeaMillions of years ago65.5135Mesozoic251PaleozoicGondwanaLaurasiaEurasiaIndiaAfricaAntarcticaAustraliaNorth AmericaMadagascarCenozoicPresentBreakupOf PangaeaContinentalDrift promotesspeciation69Figure 25.13 The history of continental drift during the Phanerozoic eon

70What Can Explain the Similar Adaptations Between Some Placental Mammals & Marsupials? Answer: Convergent Evolution71Convergent Evolution

72Convergent EvolutionEvolution that is seen when there are similarities between organisms that are NOT homologousThese similar structures would be considered to be analogous structuresAnalogous structures: similarities in structures that arise independently in different parts of the world through natural selection

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