Presentation Transcript
Slide 1:The Fossil
Record How do fossils form?
Determining their age.
What do they reveal?
Slide 2:How Do Fossils Form? Most fossils form when organisms that die become buried in sediments.
Some remains that become buried in sediments actually change to rock. Minerals dissolved in the water soak into the buried remains. Gradually, the minerals replace the remains, changing them into rock. Fossils that form this way are called petrified fossils. Sometimes shells or other hard parts buried by sediments gradually dissolve and form an empty space.
The hollow space in the sediment that is in the shape of the organism is called a mold.
When the space becomes filled in with hardened minerals, a cast, or copy of the shape of the organism is formed.
Slide 3:Sometimes organisms are preserved in substances other than sediments!
Organisms such as the mammoth have been perfectly preserved in ice.
Insects like the mosquito have been preserved in the sap of trees called amber.
Slide 4:Determining a Fossil’s Age To understand how living things have changed through time, scientists need to be able to determine the ages of fossils.
Scientists can determine fossil ages in 2 ways….. Relative Dating: A technique used to determine which of two fossils is older. Radioactive Dating: A technique used to determine the actual age of a fossil on the basis of the amount of a radioactive element it contains.
Radioactive Elements: Unstable elements that decay or break down into other elements.
Half-Life: The time it takes for half of the atoms in a sample of radioactive element to decay.
Slide 5:What do Fossils Reveal? Fossils can act like pieces in ajigsaw puzzle, helping scientists piece together information about Earth’s past. The millions of fossils that scientistshave collected are called the fossil record. A species is extinct if no members of thatspecies are still alive.