Transcript FOSSILS - Yorkville High School

FOSSILS
What is a fossil?
• Remains of once living animals or
plants
• Represent ancestors of organisms
living today
Does every organism turn into a fossil?
• No - Normally they rot or get eaten
• If the conditions are correct they can be
buried quickly and fossilized
– 5 Different steps
How are fossils formed?
1. Animal dies and is buried by sediment
2. Extreme pressure turns sediment into stone
3. Skeleton dissolves and leaves a hole/mold
–
Dissolved by ground water
4. Minerals crystallize in hole and a cast is formed
–
Mineral rich water enters mold and leaves minerals
5. Millions of years later, the fossil is exposed on the Earths
surface
– Earthquakes, mountain building, construction, digging/drilling
Why don’t all animals become fossils?
• If they aren’t covered completely
– Weathering
– Erosion
• Scavengers
What do fossils tell us?
• How plants and animals used to live and where
they used to live
– Individual? Group?
• How plants and animals from the past are related
to the ones today
• How plants and animals develop
• What type of
animals/plants used
to be present
What different types of fossils are there?
• Body fossils
– Tell us what the animal/plant
looked like
– Ex: Petrified wood, frozen
mammoths, amber
• Trace fossils
– Tell us what the animal did
– Ex. Footprints, trackways,
Coprolites (poo)
How are fossils preserved?
• Buried in ASH, MUD, OR SAND
• Frozen in ice
• Covered in tar
How do we get information about fossils?
• Relative dating
– Looking at rock Layers
• Absolute dating
– Measuring radioactive
Half-Life
How are rock layers formed?
• Rocks are…
– Melted
– Cooled
– Weathered/
Eroded
– Compacted/
Cemented
– Heated/
Pressurized
How are rock layers formed?
Rock layers = Sedimentary Rocks
– Formed when particles are
deposited on top of other
particles
– Pressure pushes down
– Dissolved minerals form natural
glue
– Creates rocks at or near the
surface
Why are rock layers important?
• Tell our history
• Geologic Column
– Arranged from oldest to youngest
• Gaps in history
– Erosion
– Folding, Faults,
Volcanoes
What do the rock layers tell us?
• When events happened
– In general rocks in the same layer happened
at the same time
• Fossils in the same layer lived at the same time
What is radioactive decay?
• Certain naturally occurring elements are
radioactive and they break down at predictable
rates
• Scientists measure the half-life of elements
– Half life = the time it takes for half the radioactive
element to break down
• Scientists compare the amount of an element to
the initial amount and the half-life to determine
age
Why is radioactive decay helpful?
• Also called carbon dating
• Allows us to calculate an age
• Cannot be used for objects older than 70,000 years