The history of the earth

1. Orhowdidyouarrivehere…. Thehistory of theearth

2. Theformation of the Solar System • Themostacceptedmodelisthe “nebular hypothesis”: theformation of the SS originatedfrom a nebula of dust and gas. • http://search.tb.ask.com/search/video.jhtml?searchfor=origin+of+the+solar+system&p2=^AYY^xdm065^YYA^es&n=77fdd03d&ss=sub&st=bar&ptb=F4BFB15C-3AAE-4E06-8816-6A5AA9E72DDA&si=flvrunner&tpr=sbt

3. Earth’sformation • Accretion of fragmentsmade of mainlysilicates. • Theheatgeneratedbythecollision of elements, meltedtheplanet and thedensermaterials moved and formedthecore. Silicatesformedmantle and crust.

4. Theage of theEarth • 17th century: 4004 years • 19th century: 40 millionyears • End of 19th century: 100 millionyears • Currentlyaccepted: 4550 millionyears

5. Datingthe record • RELATIVE DATING: consists of orderingthestrataor geological eventsrecorded in oneor more stratigraphic series chronologically. • ABSOLUTE DATING: consists of assigning a specific date toeachstratumor geological eventrecorded in a series, indicatinghowlongagoitwasformedoroccurred. -Radiometricmethods (rate of decay of elements).

6. Thestrstigraphic record • Thestratigraphic record istheinformationaboutthepastcontained in thestrata of sedimentaryrocks. • Allsedimentarybasinsoriginated at a specific time and place and, fromtheiroriginstothepresentday, theyhaveundergo a series of processesthataffectthestrataformed in them.

7. Processes: • Filling in withsediments • Diagenesis ( transformation of sedimentsintosedimentaryrocks) • Alteration of thesedimentarybasin (lithosphericdynamics: erosion, deformations, etc)

8. Theinformationcontained in thestrata. • Themaincharacteristics of a stratum are itsextension, lithologicalcomposition (types of rocks and environmentalconditions), itsfossilcontent (biodiversity in thatperiod, indexfossilsprovide more info) and itsarrangement ( geological processes).

9. Thebasicprinciples of stratigtraphy • Principle of uniformitarism: the geological processesthatacted in thepast are thesame and havethesameeffectsonrocks as today. • Priniple of thesuccession of geological events: eventsoccurredaftertheformation of therocks

10. 3.- Principle of thearrangement of thestrata: • Original horizontality: strata are formedhorizontally • Lateral continuity: a stratum has thesameagetrhoughoutitsextension • Superposition: eachlayerisolderthantheoneaboveit

11. 4.-Principle of thesuccession of fossils: Stratacontainingthesamefossilhavethesameage. Indexfossils are important. • Indexfossils: had a largegeographicaldistributionbutonlyduring a specificperiod. • Facies fossils: can onlylive in certainenvirionments. • Fossilsprovide temporal and paleoecologicalinformation. http://www.bbc.co.uk/nature/fossils/Lagerst%C3%A4tte

12. Comparingstrata

13. Natural strata

14. Fold - syncline

15. Folds: anticline

16. Folds: pliegues

17. Foldelements

18. Faults: fallas

19. Reverse fault

20. Fossilformation. Step 1 • Fossilisation only happens in the rarest of cases, when a plant or animal dies in the right circumstances. Animal corpses are usually eaten by something, or bacteria rots them away before fossilisation can occur, and even hard parts like bones and shells are eventually destroyed through erosion and corrosion. The trick to becoming a fossil is to die in a location where your body - or bits of it - are protected from scavengers and the elements. This means getting buried in sand, soil or mud and the best place for that is on the seabed or a river bed.

21. Step 1

22. Step 2 • Only in very rare cases do the soft parts of animals - the flesh, skin and internal organs - become fossils. Even when buried under mud or soil, decay still takes place, though lack of oxygen does slow it down. If a skeleton is dug up at this stage, it will still be made of bone. Remains like these that haven't truly fossilised yet are sometimes called 'sub-fossils'.

24. Step 3 • As more time passes, sub-fossils become buried deeper and deeper. What was mud or sand becomes compressed on its way to becoming rock. But even safely sealed away underground, time doesn't stand still. Chemicals and minerals percolate through the sediment and the original bone or shell gradually recrystallizes. In extreme cases, the entire thing can dissolve away, leaving a hollow where it once was. If palaeontolgists find a hollow like this, they can pour liquid rubber in to make a fossil cast, or put it in a medical scanner to see what the original looked like.

26. Step 4 • In other cases, minerals from the rocks gradually impregnate the bone, shell or wood, changing its chemical composition and making it capable of surviving for as long as - or sometimes longer than - the rock enclosing it. In cases where the original has dissolved away, the minerals can gradually fill the hollow to create a natural cast of the original. So sometimes a fossil doesn't contain anything of the original creature except its shape. Even that shape can take a battering! If the rocks are distorted and squeezed by geological forces, then the fossils within them will be too.

28. Step 5 • Even rocks have a finite lifespan. Eventually the rock enclosing a fossil is eroded away, and the fossil is revealed on the surface of the ground. With luck, a sharp-eyed fossil collector will spot and excavate it. Otherwise the elements will continue to batter it, until it - along with the rocks around it - is reduced once more to sand, silt or mud.

30. TheEarth’shistory • Geological time spans more than 4500 millionyears. Thisperiod has beendividedintointervals; thelargestunits are eons, dividedinto eras, dividedintoperiods.

31. History of lifeonEarth • The history of life on Earth began about 3.8 billion years ago, during the Archean era, initially with single-celled prokaryotic cells, such as bacteria. Multicellular life evolved over a billion years later and it's only in the last 570 million years that the kind of life forms we are familiar with began to evolve, starting with arthropods, followed by fish 530 million years ago (Ma), land plants 475Ma and forests 385Ma. Mammals didn't evolve until 200Ma and our own species, Homo sapiens, only 200,000 years ago. So humans have been around for a mere 0.004% of the Earth's history. • The Tree of Life • The Tree of Life illustrates how different species arise from previous species via descent with modification, and that all of life is connected. The diagram below shows the relationship between the major biological groups. The centre represents the last universal ancestor of all life on earth, the outer branches the major biological groups.

32. Thetree of life

33. Diagram of eons and eras

34. 4550-3800 millionyearsago • Layers of Earthformed • Firstatmosphereformed • MeteoritesbombardedtheEarth • Moonformed • At theend of theHadeaneonprimitivelifeformed

35. 3800-540 millionyearsago • Onlymicrocontinents (Archean era) • Crustgrew • Supercontinents and litosphericmovements (Proterozoic) • Meteroritebombardementstopped • Tectonicplatemovement • Oxygenappeared in atmosphere • Iron oxide rocks • Ice! Thecoldestperiod ( Cryogenian) • Firstsupercontinent: Rodinia

36. 540-250 millionyearsago • Rodiniabroke up and reunited as Pangeahttp://en.wikipedia.org/wiki/File:Pangea_animation_03.gif • Paleozoic

37. 250 -65 millionyears • Mesozoic • Pangeaseparated in present-daycontinents. • Half of thecontinentsweresubmerged and coveredwithlimestone and plankton ( petroleum)

38. 65 millionyearsago – presentday • Cenozoic • Collision of continents • Climatecooled: 18 glacial periods