Fossils & History of the Earth .

Fossils and Superposition What is a fossil? The trace or remains of an organism that lived long ago, most commonly preserved in sedimentary rock What is a superposition? Younger rocks lie above older rocks if the layers have not been disturbed

How a Fossil Forms - Fossils Most fossils form when living things die and are buried by sediment. The sediment slowly hardens into rock and preserves the shapes of the organisms.

Fossil Types 1) Mold = hollow impression of a living thing in rock after it 2) Cast = solid mineral deposit that filled a mold, leaving a copy of the living thing

Fossil Types continued Trace fossils –

Fossil Types continued . 3) Body fossils – actual parts of an organism bones, shells, leaf imprints

impressions of passage of living things Fossil Types continued 4) Burrows or borings – Spaces dug out by living things & preserved as is or filled in 5) Tracks – impressions of passage of living things

Fossil Types continued 6) Imprint – Thin objects such as a leaf that falls onto sediment & leaves an imprint then the sediment hardens into rock

parts of an organism producing a copy of them Fossil Types continued 7) Petrified Fossils Minerals penetrate & replace the hard parts of an organism producing a copy of them 8) Amber & Ice An entire organism was quickly trapped in ice or tree sap that hardens into amber

Sedimentary Rock Where are fossils found? What type of rock formation is this? Sedimentary, Metamorphic, or Igneous? Sedimentary, you can see the layers. 10

What conditions promote fossilization? 1) Hard body parts such as skeletal bones or exoskeletons 2) Rapid burial and/or lack of Oxygen

Sporadoceras Nautilus Sporadoceras, which lived during the Devonian period 350,000,000 years ago, are extinct relatives of the chambered nautilus.  The shells of these creatures accumulated on the sea floor and were buried in sediment.  Over the ages they hardened to stone.  Today they are quarried from what is now the Sahara Desert in Morocco. Nautilus 12

Orthoceras Orthoceras were marine, or sea animals similar to modern squid.  They had a shell shaped like a cone.  Orthoceras were active swimmers in warm shallow seas and swam by squirting water out of the body cavity.  They ate small animals and some grew to be 6 feet long.  In the fossilized remains of the shell, you can often see different chambers where the animal lived Squid 13

Trilobites Scientists think that trilobites were the first multiple-celled animal to exist on earth.  These extinct sea animals had exoskeletons, or outer armor, that was divided into 3 parts.  Some crawled on the sea bed, some floated and some swam.  The lived all over the world.  Crabs and lobsters are modern relatives. Lobster 14

Fossil Fish Fish are the oldest and most primitive type of vertebrate.  The first fish were small, the size of a minnow.  They had heavy, bony plates for skin.  They lived on the ocean floor and are through slits on both sides of their throats.  Later, fish began to develop gills, scales and fins and learned to live in fresh water, too.  Some even developed lungs.  Over half the species of vertebrates, both living and extinct, are fish 15

Dinosaur Bones The word dinosaur means "terrible lizard".  Dinosaurs  were reptiles that lived throughout the world and dominated the land for over 140 million years.  Some were as small as a rooster in size.  Other grew to be the largest land animals ever to live and weighed up to 80 tons.  Many dinosaurs ate plants.  Others were meat eaters.  They began to die out when the Earth's climate became colder and plant life changed. 16

- Fossils Changes Over Time The fossils record provides evidence about the history of life and past environments on Earth. The fossil record also shows that different groups of organisms have changed over time.

Changes Over Time - Fossils From fossils, scientists have reconstructed the paleomastodon. This animal had a short trunk and short tusks on both the upper and lower jaws. The paleomastodon is an ancestor of the modern elephant.

The Position of Rock Layers - The Relative Age of Rocks The Position of Rock Layers According to the law of superposition, in horizontal sedimentary rock layers, the oldest layer is at the bottom. Each higher layer is younger than the layers below it.

Determining Relative Age - The Relative Age of Rocks Determining Relative Age To determine relative age, geologists also study extrusions and intrusions of igneous rock, faults, and gaps in the geologic record.

Determining Relative Age - The Relative Age of Rocks Determining Relative Age An unconformity occurs where erosion wears away layers of sedimentary rock. Other rock layers then form on top.

Using Fossils to Date Rocks - The Relative Age of Rocks Using Fossils to Date Rocks Index fossils are useful because they tell the relative ages of the rock layers in which they occur.

Index Fossil Activity - The Relative Age of Rocks Web Site: PHSchool.com Code: cfp-2042

Asking Questions - The Relative Age of Rocks Question Answer What does the position of rock layer reveal? The oldest layers—and the oldest fossils—are at the bottom. How do geologists determine the relative age of a rock? They examine the position of rock layer, extrusions and intrusions of igneous rock, faults, and gaps in the geologic record. How are fossils used to date rocks? The age of an index fossil tells the age of the rock layer in which it occurs.

Determining Absolute Ages - Radioactive Dating Determining Absolute Ages Radioactive Decay = During radioactive decay, the atoms of one element break down to form atoms of another element.

Radioactive Decay - Radioactive Dating The half-life of a radioactive element is the amount of time it takes for half of the radioactive atoms to decay.

Determining Absolute Ages - Radioactive Dating Determining Absolute Ages Geologists use radioactive dating to determine the absolute ages of rocks.

Determining Absolute Ages - Radioactive Dating Determining Absolute Ages The age of a sedimentary rock layer can be determined relative to the absolute age of an igneous intrusion or extrusion near the sedimentary rock.

The Geologic Time Scale Because the time span of Earth’s past is so great, geologists use the geologic time scale to show Earth’s history.

Earth’s Surface Forms - Early Earth During the first several hundred million years of Precambrian Time, an atmosphere, oceans, and continents began to form.

Life Develops - Early Earth Scientists have found fossils of single-celled organisms in rocks that formed about 3.5 billion years ago. These earliest life forms were probably similar to present-day bacteria.

Mass Extinctions - Eras of Earth’s History The graph shows how the number of families of animals in Earth’s oceans has changed.

Mass Extinctions - Eras of Earth’s History Interpreting Data: How long ago did the most recent mass extinction occur? Slightly more than 50 million years ago

Mass Extinctions - Eras of Earth’s History Interpreting Data: Which mass extinction produced the greatest drop in the number of families of ocean animals? The one that occurred about 230 million years ago

Mass Extinctions - Eras of Earth’s History Relating Cause and Effect: In general, how did the number of families change between mass extinctions? The number of families of ocean animals immediately dropped but then increased.

- Eras of Earth’s History Geologic History

Continental Drift Activity - Eras of Earth’s History Continental Drift Activity Web Site: Phschool.com Code: cfp-1015