Preview

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Preview
The Fossil Record

• Section 1 Geologic History
• Section 2 Looking at Fossils
• Section 3 Time Marches On

Concept Mapping
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Bellringer
Section 1 Geologic History

• The Present is the Key to the Past was the
  cornerstone of uniformitarianist theory developed
  by geologist James Hutton in the late 1700s.
• Write a few sentences in your science journal
  about how studying the present could reveal the
  story of Earths history. Use sketches to
  illustrate processes that occurred millions of
  years ago that you can still see today.

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Objectives
Section 1 Geologic History

• Compare uniformitarianism with catastrophism.
• Describe how the science of geology has changed
  over the past 200 years.
• Contrast relative dating with absolute dating.

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The Principle of Uniformitarianism
Section 1 Geologic History

• In Theory of the Earth (1788), James Hutton
  introduced idea of uniformitarianism.
• Uniformitarianism assumes geologic processes
  shaping Earth today have been at work throughout
  Earths history.

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Section 1 Geologic History
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The Principle of Uniformitarianism, ctd
Section 1 Geologic History

• Uniformitarianism vs Catastrophism
• During Huttons time, most scientists supported
  catastrophism, principle that all geologic change
  occurs suddenly.
• Earths mountains, canyons, seas formed by
  rare, sudden events ? catastrophes.

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The Principle of Uniformitarianism, ctd
Section 1 Geologic History

• Most people also believed that Earth was only a
  few thousand years old.
• Huttons work suggested very different reality.
• Earth much older ? gradual geologic processes
  would take much longer than few thousand years.

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The Principle of Uniformitarianism, ctd
Section 1 Geologic History

• Victory for Uniformitarianism
• Catastrophism ? guiding principle of geology in
  early 19th century.
• Uniformitarianism ? geologys guiding principle
  after Charles Lyell reintroduced concept in
  Principles of Geology (1830-1833).

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The Principle of Uniformitarianism, ctd
Section 1 Geologic History

• Lyell successfully challenged catastrophism
  using
• Huttons notes
• evidence of his own
• Saw no reason to doubt that major geologic change
  happened at same rate in past as it happens in
  present ? gradually.

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Modern GeologyA Happy Medium
Section 1 Geologic History

• During late 20th century, scientists such as
  Stephen J. Gould challenged principle of
  uniformitarianism.
• Believed that catastrophes sometimes play an
  important role in shaping Earths history.
• Neither theory completely accounts for all
  geologic change.

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Modern GeologyA Happy Medium, ctd
Section 1 Geologic History

• Most geologic change is gradual uniform.
• But catastrophes that cause geologic change have
  occurred during Earths long history.
• Asteroid, comet strikes to Earth, for example,
  caused rapid change.

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Modern GeologyA Happy Medium, ctd
Section 1 Geologic History

• Some scientists think asteroid strike 65 MYA
  caused mass extinction of dinosaurs.

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Section 1 Geologic History

• 2 scientific methods to determine age of objects
  in sedimentary rocks
• relative dating examines a fossils position
  within rock layers to estimate its age.
• absolute dating scientists examine atoms to
  measure age of fossils or rocks in years.

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Relative Dating
Section 1 Geologic History

• Bottom layers of rock usually oldest, with top
  layers usually youngest.
• Scientists can use order of these rock layers to
  determine relative age of objects w/in layers.
• fossils in bottom layers ? usually older than
  fossils in top layers.

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Relative Dating, ctd
Section 1 Geologic History

• To make relative dating easier, geologists
  combine data from all known rock sequences around
  world.
• geologic column ideal sequence of rock layers
  that contains all known fossils rock formations
  on Earth (layers arranged from oldest to
  youngest)

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Section 1 Geologic History
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Absolute Dating
Section 1 Geologic History

• Scientists can use absolute dating to more
  precisely determine age of fossil or rock.
• absolute dating ? scientists examine atoms to
  measure age of fossils or rocks in years.
• Atoms particles that make up all matter.

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Absolute Dating, ctd
Section 1 Geologic History

• Some atoms are unstable, will decay over time.
• When an atom decays ? becomes a different and
  more stable kind of atom.
• Each kind of unstable atom decays at own rate.

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Absolute Dating, ctd
Section 1 Geologic History

• half-life time it takes for half of unstable
  atoms in a sample to decay
• Scientists can examine sample of rock or fossil,
  and look at ratio of unstable to stable atoms.
• Since half-life is known, can determine
  approximate age of sample.

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Section 1 Geologic History
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Absolute Dating, ctd
Section 1 Geologic History

• Uranium-238 has a half-life of 4.5 billion yrs
• Uranium-238 used to date rocks or fossils
  millions of years old.
• Carbon-14 has a half-life of only 5,780 yrs
• Carbon-14 used to date fossils other objects
  lt50,000 years old, such as human artifacts.

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PaleontologyThe Study of Past Life
Section 1 Geologic History

• Paleontology science of study of past life, esp
  using fossils ? remains of organisms preserved by
  geological processes.
• Paleontologists collect data by studying fossils.

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PaleontologyThe Study of Past Life, ctd
Section 1 Geologic History

• Vertebrate and invertebrate paleontologists ?
  study remains of animals.
• Paleobotanists ? study fossils of plants.
• Other paleontologists
• reconstruct past ecosystems
• study traces that animals left behind
• piece together conditions under which fossils
  formed

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Bellringer
Section 2 Looking at Fossils

• Describe the fossil record of your own life that
  might be found 65 million years from now. What
  items, or artifacts, might be likely to survive?
  What kinds of things would decay and disappear?
  Do you think your fossil record would produce an
  accurate picture of your life? What might be
  missing?
• Write your description in your science journal.
  Later, you will share your description with the
  class.

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Objectives
Section 2 Looking at Fossils

• Describe five ways in which different types of
  fossils form.
• List three types of fossils that are not part of
  organisms.
• Explain how fossils can be used to determine the
  history of changes in environments and organisms.
• Explain how index fossils can be used to date
  rock layers.

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Fossilized Organisms
Section 2 Looking at Fossils

• Fossil remains or physical evidence of an
  organism preserved by geologic processes
• Fossils in rocks can form when an organism dies ?
  quickly covered by sediment.
• When sediment becomes rock, hard parts of the
  organism are preserved.

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Fossilized Organisms, ctd
Section 2 Looking at Fossils

• Insect caught in sticky tree sap ? sap covers
  its entire body and hardens quickly.
• Fossils in amber ? entire organisms preserved
  inside hardened tree sap amber.
• Some of best insect fossils, as well as frogs and
  lizards, found in amber.

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Fossilized Organisms, ctd
Section 2 Looking at Fossils

• Organisms can also be preserved by petrifaction.
• Petrifaction process in which minerals replace
  organisms tissues.
• Permineralization
• Replacement

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Fossilized Organisms, ctd
Section 2 Looking at Fossils

• Permineralization pore space in an organisms
  hard tissue (like bone or wood) is filled up with
  mineral.
• Replacement minerals completely replace tissues
  of the organism.
• Some samples of petrified wood are composed
  completely of minerals.

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Fossilized Organisms, ctd
Section 2 Looking at Fossils

• In some places, tar wells up and forms thick,
  sticky pools at Earths surface.
• These tar pools can trap and preserve many
  organisms.
• The La Brea tar deposits in Los Angeles,
  California have preserved organisms for at least
  38,000 years.

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Fossilized Organisms, ctd
Section 2 Looking at Fossils

• Frozen Fossils
• In 1999, scientists removed 20,000-year-old
  woolly mammoth frozen in Siberian tundra.
• became extinct 10,000 years ago
• cold temps slow decay ? mammoth almost perfectly
  preserved

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Other Types of Fossils
Section 2 Looking at Fossils

• Trace fossils any naturally preserved evidence
  of animal activity.
• EX Tracks ? form when animal footprints fill
  with sediment.
• Reveal
• size and speed of animal
• whether it traveled in groups

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Other Types of Fossils, continued
Section 2 Looking at Fossils

• EX Burrows ? shelters made by animals that bury
  themselves in sediment, such as clams.
• EX Coprolite ? preserved animal dung.

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Other Types of Fossils, ctd
Section 2 Looking at Fossils

• Molds and casts are two more examples of fossils.
• MOLD cavity in rock where a plant or animal was
  buried
• CAST an object created when sediment fills a
  mold and becomes rock.

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MOLD FOSSIL

• One form of fossil forms when an organism dies
  and its body is covered by layers of sediment.
• As time passes, the organism itself, particularly
  when composed primarily of softer materials, is
  eroded and carried away, leaving a negative
  imprint of its body.

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CAST FOSSIL

• Forms when a mold fossil is filled with some form
  of mineral, usually through the seepage of water
  depositing minerals within the mold.
• In time, the mold is filled and deposited
  materials harden, creating a replica
  of original fossil.

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• CAST FOSSILS

• MOLD FOSSIL

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Section 2 Looking at Fossils

• Information in the Fossil Record
• The fossil record gives only rough sketch of
  history of life on Earth.
• Most organisms never become fossils.
• Many fossils have yet to be discovered.

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Using Fossils to Interpret the Past, ctd
Section 2 Looking at Fossils

• Organisms with hard body parts have left more
  fossils than those with soft body parts.
• Bone vs cartilage
• Shells vs skin
• Organisms that lived in areas that favored
  fossilization have also left more fossils.

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Using Fossils to Interpret the Past, ctd
Section 2 Looking at Fossils

• But fossils can show a history of environmental
  change.
• EX presence of marine fossils on mountaintops
  in Canada ? mountains formed at bottom of ocean.
• Marine fossils can also help scientists
  reconstruct ancient coastlines and detect the
  presence of ancient seas.

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Using Fossils to Interpret the Past, ctd
Section 2 Looking at Fossils

• Scientists can use fossils of plants/land animals
  to reconstruct past climates.
• By examining fossils, scientists can tell whether
  climate of area was cooler/wetter than now.

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Using Fossils to Interpret the Past, ctd
Section 2 Looking at Fossils

• History of Changing Organisms
• Scientists study relationships between fossils to
  interpret how life has changed over time.
• Since the fossil record is incomplete,
  paleontologists look for similarities between
  fossils over time to try to track change.

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Using Fossils to Date Rocks
Section 2 Looking at Fossils

• Scientists have found that particular types of
  fossils appear only in certain layers of rock.
• By dating rock layers above and below these
  fossils, scientists can determine time span in
  which organism lived.
• If organism lived for relatively short period of
  time, its fossils would show up in limited layers.

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Using Fossils to Date Rocks, ctd
Section 2 Looking at Fossils

• Index fossils fossils of organisms that lived
  for relatively short, well-defined geologic time
  span.
• To be index fossils, these fossils must be found
  worldwide.

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Using Fossils to Date Rocks, ctd
Section 2 Looking at Fossils

• These ammonites were marine mollusks similar to
  modern squids.
• Tropites lived between 230 - 208 MYA
• Fossils of these ammonites are index fossils for
  that time period.

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Using Fossils to Date Rocks, ctd
Section 2 Looking at Fossils

• Trilobites of genus Phacops are also index
  fossils.
• Trilobites are extinct. Their closest living
  relative is the horseshoe crab.

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Using Fossils to Date Rocks, continued
Section 2 Looking at Fossils

• Ammonites of the genus Tropites are index fossils.

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Using Fossils to Date Rocks, ctd
Section 2 Looking at Fossils

• Phacops lived about 400 MYA
• When scientists find fossils of trilobites
  anywhere on Earth, they assume rock layers are
  also approximately 400 MYO.

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MAJOR INDEX FOSSILS
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Bellringer
Section 3 Time Marches On

• Archaeologists and paleontologists believe that
  modern humans have lived on Earth for 150,000 to
  200,000 years. If we imagine the history of the
  Earth to be the length of one calendar year, on
  which date do you think modern humans arrived?
• Record your answer in your science journal.

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Objectives
Section 3 Time Marches On

• Explain how geologic time is recorded in layers
  of sedimentary rock.
• Explain how the geologic time scale illustrates
  the occurrence of processes on Earth.
• Explain how the fossil record provides evidence
  of changes that have taken place in organisms
  over time.

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Geologic Time
Section 3 Time Marches On

• Earth is 4.6 billion years old. (The Acasta
  Gneiss rock outcrop in Northwest Territories,
  Canada, is oldest known crustal rock outcrop in
  world, 4 BYO, by zircon crystal dating.)
• Paleontologists find record of Earths history in
  rock formations and fossils around world.

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Dinosaur National Monument (UT) contains remains
of thousands of dinosaurs that inhabited area
150 MYA.
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Geologic Time, ctd
Section 3 Time Marches On

• Although 150 million years seems like incredibly
  long period, is little more than 3 of time Earth
  has existed.
• The Rock Record and Geologic Time One of best
  places in North America to see Earths history
  recorded in rock layers is Grand Canyon National
  Park, AZ.

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Grand Canyon National Park, AZ
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Geologic Time, ctd
Section 3 Time Marches On

• Colorado River has cut Grand Canyon nearly 2 km
  deep in some places.
• Over course of 6 million years, river has eroded
  countless layers of rock.
• These layers represent almost half, or nearly 2
  billion years, of Earths history.

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Geologic Time, ctd
Section 3 Time Marches On

• The Fossil Record and Geologic Time
• Sedimentary rocks in Green River formation can be
  found in parts of WY, UT, and CO.
• These rocks are thousands of meters thick, once
  part of ancient lake system that existed for
  millions of years.
• Fossils of plants and animals are common in these
  rocks ? very well preserved.

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The Geologic Time Scale
Section 3 Time Marches On

• The geologic column represents billions of years
  that have passed since the first rocks formed on
  Earth.
• geologic time scale a scale that divides Earths
  history into distinct intervals of time.

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Section 3 Time Marches On
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The Geologic Time Scale, ctd
Section 3 Time Marches On

• Geologists have divided Earths history into
  sections of time.
• Eons largest divisions of time
• Hadean eon
• Archean eon
• Proterozoic eon
• Phanerozoic eon

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The Geologic Time Scale, ctd
Section 3 Time Marches On

• The Phanerozoic eon is divided into three eras,
  second-largest divisions of geologic time.
• The three eras are further divided into periods,
  third-largest divisions of geologic time.
• Periods are divided into epochs, fourth-largest
  divisions of geologic time.

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GEOLOGIC TIME PERIODS

• EONS ? ERAS ? PERIODS ? EPOCHS

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The Geologic Time Scale, ctd
Section 3 Time Marches On

• Boundaries between geologic time intervals
  represent shorter intervals in which visible
  changes took place on Earth.
• Some changes are marked by disappearance of index
  fossil species.
• Other changes can be recognized only by detailed
  paleontological studies.

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The Geologic Time Scale, ctd
Section 3 Time Marches On

• The Appearance Disappearance of Species
• At certain times during Earths history, number
  of species increased or decreased dramatically.
• Sudden increase in species ? often result of
  relatively sudden increase or decrease in
  competition between species.

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The Geologic Time Scale, ctd
Section 3 Time Marches On

• Hallucigenia sparsa appeared during Cambrian
  period, when number of marine species greatly
  increased.

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The Geologic Time Scale, continued
Section 3 Time Marches On

• Number of species can dramatically decline over
  relatively short period of time ? result of mass
  extinction event.
• Extinction death of every member of a species.
• Gradual events such as global climate change and
  changes in ocean currents can cause mass
  extinctions.

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Section 3 Time Marches On

• The Paleozoic EraOld Life
• Paleozoic era lasted from 543 - 248 MYA
• Paleozoic era first era well represented by
  fossils.
• Marine life flourished at beginning of Paleozoic
  era. However there were few land animals.

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The Geologic Time Scale, ctd
Section 3 Time Marches On

• By middle of Paleozoic era ? all modern groups of
  land plants had appeared.
• By end of Paleozoic ? amphibians reptiles lived
  on land, insects were abundant.
• The following slide shows what life might have
  looked like in late Paleozoic era.

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The Late Paleozoic Era
Section 3 Time Marches On
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The Geologic Time Scale, ctd
Section 3 Time Marches On

• The Paleozoic era came to an end with the largest
  mass extinction in Earths history.
• Some scientists believe that ocean changes were
  likely cause of extinction.
• The event killed nearly 90 of all species.

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Section 3 Time Marches On

• The Mesozoic EraThe Age of Reptiles
• began about 248 million years ago.
• Called Age of Reptiles because reptiles such as
  dinosaurs dominated.

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The Geologic Time Scale, ctd
Section 3 Time Marches On

• Small mammals appeared about same time that
  dinosaurs did.
• Birds appeared in late Mesozoic era.
• Many scientists think birds developed directly
  from a type of dinosaur.

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The Geologic Time Scale, ctd
Section 3 Time Marches On

• At end of Mesozoic era, 15 - 20 of all species
  on Earth became extinct.
• mass extinction event wiped out the dinosaurs
• Global climate change may have caused this
  extinction.

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Section 3 Time Marches On

• Cenozoic EraThe Age of Mammals
• The Cenozoic era began about 65 MYA, continues to
  the present.
• This era is known as Age of Mammals.
• During Mesozoic era, mammals had to compete with
  dinosaurs, other animals for food habitat.

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CENOZOIC ERA
Section 3 Time Marches On

• After mass extinction at end of Mesozoic era,
  mammals flourished.
• Unique traits may have helped these mammals
  survive environmental changes that probably
  caused dinosaur extinction.
• These traits include ability to regulate internal
  body temperature, to develop young inside mother.

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Concept Mapping
The Fossil Record
Use the terms below to complete the concept map
on the next slide. rock layers atoms relative
dating fossils decay absolute dating
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The Fossil Record
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The Fossil Record