217-1 The Fossil RecordPhoto credit: Jackie Beckett/American Museum of Natural History
3Fossils and Ancient Life What is the fossil record?It is NOT an Elvis Presley record!
4Fossils and Ancient Life Paleontologists are scientists who collect and study fossils.All information about past life is called the fossil record.The fossil record includes information about the structure of organisms, what they ate, what ate them, in what environment they lived, and the order in which they lived.
5Fossils and Ancient Life The fossil record provides evidence about the history of life on Earth. It also shows how different groups of organisms, including species, have changed over time.Fossils and Ancient Life
6Fossils and Ancient Life The fossil record provides incomplete information about the history of life.Over 99% of all species that have lived on Earth have become extinct, which means that the species has died out.
7How Fossils FormHow Fossils FormFossils can be as large as a complete, preserved animals, or as small as a fragment.Most fossils form in sedimentary rock.Sedimentary rock forms when exposure to the elements breaks down existing rock into small particles of sand, silt, and clay.
8Fossil Formation Water carries small rock particles to lakes and seas. How Fossils FormFossil FormationWater carries small rock particles to lakes and seas.The fossil record provides evidence about the history of life on Earth. Most fossils are formed in sedimentary rock.
9Dead organisms are buried by layers of sediment, which forms new rock. How Fossils FormDead organisms are buried by layers of sediment, which forms new rock.The fossil record provides evidence about the history of life on Earth. Most fossils are formed in sedimentary rock.
10The preserved remains may be later discovered and studied. How Fossils FormThe preserved remains may be later discovered and studied.The fossil record provides evidence about the history of life on Earth. Most fossil formed in sedimentary rock.
11Interpreting Fossil Evidence Paleontologists determine the age of fossils using relative dating or radioactive dating.
12Interpreting Fossil Evidence What information do relative dating and radioactive dating provide about fossils?
13Interpreting Fossil Evidence Relative DatingIn relative dating, the age of a fossil is determined by comparing its placement with that of fossils in other layers of rock.Rock layers form in order by age—the oldest on the bottom, with more recent layers on top.Law of Horizontality- sedimentary rocks layed down horizontal, next layer on top etc.
15Interpreting Fossil Evidence Index fossils are used to compare the relative ages of fossils.An index fossil is a species that is recognizable and that existed for a short period but had a wide geographic range.
16Interpreting Fossil Evidence Relative dating allows paleontologists to estimate a fossil's age compared with that of other fossils.It does not give an actual age- only a relative age ….. This is older than that type thing.
17Interpreting Fossil Evidence Radioactive Dating Scientists use radioactive decay to assign an absolute age to rocks.Some elements are radioactive and steadily break down into nonradioactive elements.
18Interpreting Fossil Evidence Radioactive dating is the use of half-lives to determine the age of a sample.A half-life is the length of time required for half of the radioactive atoms in a sample to decay.
19Interpreting Fossil Evidence Radioactive dating involves measuring the amounts of radioactive isotopes in a sample to determine its actual age. Such measurements enable scientists to determine the absolute age of rocks and the fossils they contain.
20Interpreting Fossil Evidence In radioactive dating, scientists calculate the age of a sample based on the amount of remaining radioactive isotopes it contains.Interpreting Fossil Evidence
21Interpreting Fossil Evidence Carbon-14 begins to decay when an organism dies.Carbon-12 is not radioactive and does not decay.By comparing the amounts of carbon-14 and carbon-12 in a fossil, researchers can determine when the organism lived.Carbon -14 releases particles at a know consistent rate.
22Interpreting Fossil Evidence Carbon-14 has a useful range in dating fossils of up to about 60,000 years. It has a half life of 5,730 years.This means that in 5, ½ of the C14 will be released and it will be N14.By comparing the the ratio of C12 to C14 in a living organism and a dead one, it is possible to determine how old something is or how long agao it died.
23Interpreting Fossil Evidence If it is found that ½ of the C14 is present from what is found in a live organism, then 5,730 years have passed or 1 half life.If ¼ is found, that is 2 half lives or 11,1460 years.What if 1/16 of the C14 was found in a fossil. How many half lives would that be and how long ago did the organism die?
24Interpreting Fossil Evidence Other radioactive isotopes are used to date older rocks and fossils.Uranium 235 changes to Lead 207 in 700,000,000 years, so it has a useful range of over 500,000 years.Potassium-40 changes to Argon -40 in 1.25 billion yearsUranium-23 to Lead 206 in 4.5 billlion years so it is used to date really old thiongs over 100 million years old.* To use the wrong isotope would yield large amounts of error and is not useful or accurate.
25Geologic Time ScaleGeologic Time ScaleWhat are the main divisions of the geologic time scale?
26Geologic Time ScalePaleontologists use a scale called the geologic time scale to represent evolutionary time.Scientists first developed the geologic time scale by studying rock layers and index fossils worldwide.
27The basic divisions of the geologic time scale are eras and periods.
28Geologic Time ScaleGeologic time begins with Precambrian Time, which covers about 88% of Earth’s history.The basic units of the geologic time scale after Precambrian Time are eras and periods. Each era is divided into periods.Vendian650–544
29Geologic Time ScaleEras Geologists divide the time between Precambrian time and the present into three eras:Paleozoic EraMesozoic EraCenozoic Era
30The Paleozoic began about 544 million years ago. Geologic Time ScaleThe Paleozoic began about 544 million years ago.Many vertebrates and invertebrates lived during this time.
31Permian 290–245 360–290 Carboniferous 410–360 Devonian Silurian Geologic Time ScalePermian290–245Carboniferous360–290Devonian410–360The basic units of the geologic time scale after Precambrian Time are eras and periods. Each era is divided into periods.Silurian440–410Ordovician505–440Cambrian544–505
32The Mesozoic began about 245 million years ago. Geologic Time ScaleThe Mesozoic began about 245 million years ago.Dinosaurs lived during this time.Mammals began to evolve during this era.
33Cretaceous 145–65 Jurassic 208–145 Triassic 245–208 Geologic Time ScaleCretaceous145–65Jurassic208–145The basic units of the geologic time scale after Precambrian Time are eras and periods. Each era is divided into periods.Triassic245–208
34Mammals became common during the Cenozoic. Geologic Time ScaleThe Cenozoic began about 65 million years ago and continues to the present.Mammals became common during the Cenozoic.
35Geologic Time ScaleThe basic units of the geologic time scale after Precambrian Time are eras and periods. Each era is divided into periods.
36Geologic Time ScalePeriods Eras are subdivided into periods, which range in length from tens of millions of years to less than two million years.Many periods are named for places around the world where geologists first discovered the rocks and fossils of that period.
37Clock Model of Earth’s History Geologic Time ScaleClock Model of Earth’s HistoryFirst humansRadiation of mammalsFirst land plantsFirst prokaryotesFirst multicellular organismsCenozoic Era Mesozoic Era Paleozoic Era Precambrian TimeEarth’s history is often compared to a familiar measurement, such as the twelve hours between noon and midnight. In such a comparison, notice that Precambrian Time lasts from noon until after 10:30 pm.First eukaryotesAccumulation ofatmosphericoxygen
39Which of the following statements about fossils is NOT true? 17-1Which of the following statements about fossils is NOT true?Most fossils form in sedimentary rock.Fossils occur in a particular order.Only a small portion of fossils are from extinct organisms.Fossils can be used in relative dating of rock formations.
40The fossil record consistently shows evidence that 17-1The fossil record consistently shows evidence thatall forms of life have existed in all geologic eras.living organisms have only been on Earth for a short time.living things have changed over time.ancient life-forms are much the same as forms found living today.
41were widely distributed and existed for a very long time. 17-1Index fossils assist paleontologists in dating rocks because they represent species thatwere widely distributed and existed for a very long time.existed in a single location for a short period of time.were widely distributed and existed for a short time.existed in a single location for a very long time.
4217-1Determining the age of a fossil by comparing its placement with fossils in other layers of rock is calledcarbon-14 dating.fossil-indexing.relative dating.absolute dating.
43According to the geologic time scale, geologic time begins with 17-1According to the geologic time scale, geologic time begins withPrecambrian Time.the Paleozoic Era.the Quaternary Period.the Cambrian Era.