most fossils form when organisms that die become buried in sediments
sediments- particles of soil and rock
petrified fossils
formed when minerals dissolved in water soak into the remains gradually the minerals replace the remains changing them into a rock
chemical sedimentary rocks
Molds and Casts
Sometimes the remains themselves completely dissolve, leaving a hollow imprint in the rock
Mold- a hollow space in sediment in the shape of the organism
Cast - a copy of the shape of the organism that made the molds
Preserved Remains
organisms that remain intact or nearly intact because of the method in which it was fossilized i.e. in amber.ice
Determining a Fossil’s Age
relative dating
comparing two fossils and determing which one is older than the other - does not determind the fosisls actuals age
the deeper the fossil is buried the older it is
radioactive dating
does determine the actual age of a fossil
the rocks of the fossils are found near contain radioactive elements and decay obertime into new elements
dv time it takes for half of the atoms in a sample to decay (where the lines intersect)
scientists compare the amount of radioactive elements into which it breaks down
What Do Fossils Reveal?
extinct organisms
a species is extinct if no members of that species are still alive
the geologic time scale
a calendar of the history of life on earth
the precambrian time is the largest span of time in the GTS, covering the first 4 billion years of life on earth
Unaswered Questions
mass extinctions
when multiple species become extinct at the same time
hypothesized to be caused by a major climate change which can be caused by an asteroid, volcanic eruption, etc.
gradualism
gradualism proposes that evolution occurs slowly and that itny changes in a species gradually add up to major changes over long periods of time
does not account for the large gaps in the fossil record we would expect to see intermediate forms perhaps the fossil record is just incomplete
punctuated equilibria
punctuated equilibria proposes that species evolve quickly during a relatively short amount of time and separated by long periods of little to no change
Want to print your doc? This is not the way.
Try clicking the ⋯ next to your doc name or using a keyboard shortcut (
Fossils