Presentation on theme: "Relate Cause and Effect Why have so few organisms become fossilized"— Presentation transcript:
1 Relate Cause and Effect Why have so few organisms become fossilized Draw Conclusions Many more fossils have been found since Darwin’s day, closing many fossil gaps. How would this information make relative dating more accurateReview Describe three processes that have affected life on Earth
3 PaleontologistsResearchers who study fossils to learn about ancient life.
4 Fossils vary enormously in size, type, and degree of preservation Form only under certain conditions.
5 Types of FossilsFossils can be as large and perfectly preserved as an entire animalWith hair, skin, scales, or feathersBe as tiny as bacteria, developing embryos, or pollen grainsMany are just fragmentsTrace fossilsCasts of footprints, burrows, tracks, or even droppings.
6 Fossils in Sedimentary Rock Most commonSedimentary rock usually forms when small particles of sand, silt, or clay settles to the bottom of a body of waterCovers dead animals as it builds up.
7 Layers of sediment continue to build up over time Remains are buried deeper and deeperPressure gradually compresses sediment into rock.
8 Preserved remains may later be discovered and studied.
9 Usually soft body structures decay quickly after death Usually only hard parts like wood, shells, bones, or teeth remainHard structures can be preserved if they are saturated or replaced with minerals.
10 Soft tissues can be preserved from aerobic decay if buried quickly.
11 Fossil InformationBone structure and trace fossils, like footprints, indicate how animals movedFossilized plant leaves and pollen suggest whether the area was a swamp, a lake, a forest, or a desertComparing body structures in fossils to body structures in living organisms offer clues about how body structures and species have evolved.
12 Relative DatingPlaces rock layers and their fossils into a temporal sequenceLower layers of sedimentary rock and fossils are generally older than upper layers.
13 Index FossilsDistinctive fossils used to establish and compare the relative ages of rock layers and the fossils they containEasily recognized and will occur in only a few rock layers.
14 Radiometric DatingUses radioactive isotopes, which decay, or break down, into nonradioactive isotopes at a steady rateCompares the amount of radioactive to nonreactive isotopes in a sample to determine its age.
15 Half LifeTime required for half of the radioactive atoms in a sample to decayThe half-life of potassium-40 is 1.26 billion years.
16 Carbon-14Radioactive form of carbon naturally found in the atmosphere that is taken up by living organisms along with “regular” carbonUsed to date material that was once aliveHalf-life of only about 5730 yearsuseful for dating fossils no older than about 60,000 years.
17 Fossils older than 60,000 years Can’t use Carbon 14Use other elements to date surrounding rock.
18 Geologic Time Scale Based on both relative and absolute dating Major divisions of the geologic time scale are eons, eras, and periods.
21 Changing PlanetBuilding mountains, opening coastlines, changing climates, and geological forces have altered habitatsActions of living organisms over time have changed conditions in the land, water, and atmosphere of planet Earth.
22 Physical Forces“Heat wave” of the Mesozoic Era, average temperatures were only 6°C to 12°C higher than 20th centuryIce ages had average temperatures only about 5°C cooler than 20th century.
23 Plate TectonicsTheory that explains how solid continental “plates” move slowly above Earth’s molten core (continental drift).
24 Biological ForcesProterozoic Eon photosynthetic organisms produced oxygen gas and also removed large amounts of carbon dioxide from the atmosphereProvided oxygen for aerobic processesRemoved carbon dioxide which cooled the planet.