Topic 6 Fossils Flashcards
What are fossils
The remains of organisms from many thousand of years ago which are found in rocks
What do fossils provide evidence of
They organisms lived Ages ago
What can fossils tell you
How old the animal was and how it evolved overtime
What three ways do fossils form
Gradual replacement by minerals
Casts and impressions
Preservation In places where no decay happens
How do fossils form from gradual replacement by minerals
Most fossils are formed this way
Teeth, Shells, bones don’t decay if so can last a long time when buried
there eventually replaced by minerals as they decay forming a rocklike substance
The surrounding sediment also turns to rock and a fossil stays distinct inside the rock
How are fossils Cast and impressions
Sometimes fossils are formed when an organism is buried in a soft material like clay
clay hardens around it and the organism decays leaving a cast of itself e.g animals burrow or a plant roots can be preserved as casts
things like footprints have also been pressed into materials when soft leaving an impression
How can fossils before from preservation in places where no decay happens
In Amber and tar pitsthere is no oxygen or moisture so decay microbes can’t survive
In glaciers it’s too cold for decay microbes to work
Peat bogs are too acidic for decay microbes
Hypotheses about how life first came to being
First life forms came into existence in a primordial swamp here on Earth
maybe simple organic molecules were brought to earth on comets
these could’ve been more complex organic molecules and eventually form simple life forms
Why can’t this hypothesis be Supported or disproved
Many early life forms with softbodied which tends to decay away completely so fossil record is incomplete
Fossils that did for millions of years ago we have been destroyed by geological activity
E.g the movement of tectonic plates may have crushed fossils
