The Record of Time Science Grade 8

What are Fossils? Fossil – remains or evidence of once living organisms. Most fossils are made from mineralized bones. Process: Water dissolves in porous bones and become hard like a rock. Most are hard body parts (petrified fossil) They are frozen in soil or ice, dehydrated in caves, trapped in amber Found mostly in sedimentary rock. 5 main types of fossils:

FIVE MAIN TYPES OF FOSSILS Petrified Fossils Molds and Casts Carbon Films Trace Fossils Preserved Remains

How Reliable is the Fossil Record? Fossil Record – made up of all fossils ever discovered. It provides evidence that species have changed over time. Biased due to: Search for fossils is unequal between continents. Climate Structures not being preserved the same way It is important to be careful with assessing individual fossils. Why should we assess a group of the same species instead of just an individual? Some individuals may have illnesses or deformities that is not normal to their species. Gaps in the fossil record create “missing links” Shows changes among species over time

What Do The Fossils Tell Us? Evolutionary processes (how species evolved over time) Reconstruct body shapes Through fossils we can determine: Gender Physical capabilities Growth patterns Life expectancy Movement Size/shape/position of organs How humans and Earth have changed over time

Dating Techniques Types: Relative dating – determination of the age of a rock or geologic event by comparing with other rocks/geologic events Types: The Law of Superposition The Law of Original Horizontality The Law of Cross Cutting Relationships The Law of Lateral Continuity The Law of Included Fragments Date fossils based on the strata found (same strata = same timeframe) Relative dating is not always accurate due to unconformities. Unconformity – missing layers in the rock record due to erosion

Dating Techniques Absolute Dating – the process of establishing the age of an object by determining the number of years it has existed. Measured through Radioactive decay Biological clock (example: tree rings)

Index Fossils Index fossils – a tool used to determine the relative age of rock layers. Index fossils existed only during specific spans of time before becoming extinct. If you use absolute dating to get an age for the fossil, then you know that the rock the fossil is found in is also that age.