Fossils Flashcards
What are fossils?
Remains of organisms from many years ago found in rocks
What are the three ways in which fossils are formed?
From gradual replacement by minerals
From casts and impressions
From preservation in places where no decay happens
Describe gradual replacement by minerals?
Things like teeth shells and bones don’t decay very easily
They are eventually replaced by minerals as they decay forming a rock like substance in its origami shape
The surrounding sediment also turns to rock but the fossils stays distinct inside the rock and eventually someone digs it up
What is the most common formation of fossils?
Gradual replacement by minerals
Describe fossil formation from casts and impressions?
When an organism is buried in a soft material like clay the clay hardens around it and the organism decays leaving a cast of itself
An animals burrow or a plants roots can be preserved as cast
Things like footprints can be or see into these material when it’s soft leaving an impression when it hardens
Describe the formation of fossils from preservation?
In amber and tar pits there’s no oxygen or moisture so decay microbes can’t survive
In glaciers it’s too cold for the decayed microbes to work
Peat bogs are too acidic
The animals remains are preserved
What do fossils show?
How living things have evolved
Evidence of extinct organisms
What are two theories about where life came from?
Primordial swamp
On comets
Why are these two theories not believed?
Can’t be supported or disproved because there is a lack of valid and reliable evidence
Why do many scientists believe?
Many early organisms were soft bodies and soft tissue tends to decay completely making the fossil record incomplete
What is the other problem with fossil reliability?
Fossils that formed millions of years ago may have been destroyed by geological activity
