How do we know about the past? Fossils

What is a fossil? A fossil is an impression, cast, original material or track of any animal or plant that is preserved in rock after the original organic material is transformed or removed.

Material that has replaced the once living thing A fossil may be: an original skeleton or shell; a mold or cast; traces such as footprints or worm tubes Material that has replaced the once living thing

Types of Fossils Body fossils – actual parts of an organism bones, shells, leaf imprints

Types of Fossils Trace fossils – evidence of life having been there tracks, burrows, casts

Trace Fossils Mold – reproduction of the inside or outside surface of a living thing Cast – duplicate of the original organism; usually formed by replacement of inside of living thing Molds and casts are actually two common types of trace fossils. A mold forms when something is pressed into soft mud and removed by decomposition or pulled out, leaving an impression of the object. A cast is a 3-D example of an object of the past created when a mold fills up with sediment like mud, sand or volcanic ash.

Trace Fossils Burrows or borings – Spaces dug out by living things & preserved as is or filled in Tracks – impressions of passage of living things

Trace Fossils Imprint – Thin objects such as a leaf that falls onto sediment & leaves an imprint then the sediment hardens into rock

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

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

Why sedimentary rock? The animal dies and lies on the ground or sinks to the sea floor. The body begins to decay and is buried under layers of sediment such as mud or sand. These layers eventually become sedimentary rock. http://web.ukonline.co.uk/conker/fossils/how-fossils-were-made.htm 11

Putting it all together Examples of Fossils . . . 12

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 13

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. 14