fossil record - paleontology geo-science
Post on 15-Apr-2017
558 Views
Preview:
TRANSCRIPT
What is the Fossil record ? M8
Provides evidence about the history of life on earth and its evolution.
The total number of fossils that have been discovered , as well as to the information derived from them.
M8 Why is it incomplete ?
The fossil record is very incomplete because of :
1 ) fossils are rare , because fossilization require specific conditions. E.g., only animals have hard body , can fossilize.
2 ) not all the fossils have been found.
Seek the peak Why is it incomplete ?
3 ) dead organisms are destroyed by : Predators ( wild animals ) Water damage Climate , before they fossilize .
4 ) fossils destroyed and degenerate over time
Thus the oldest fossils might turn to dust.
Seek the peak Romer's Gap
is an example of an apparent gap in the tetra pod fossil record Such gaps represent periods from which excavators have not yet found relevant fossils.
Romer's gap spanned from approximately 360 to 345 million years ago, corresponding to the first 15 million years of the Carboniferous Period.
Some scientists have suggested that the geochemistry caused bad conditions for fossil formation, so few organisms were fossilized.
Another theory suggests that scientists have not yet discovered an excavation site for these fossils, due to inaccessibility or random chance.
Seek the peak Principle of superposition
•Principle of Original Horizontality:
because strata are deposited under gravity, they form horizontal layers. If the strata are no longer horizontal, something has disturbed the sediments
•Principle of Superposition:
unless they have been disturbed, the strata at the bottom of a stack were deposited first, the ones on top of that are next oldest, and so on, with the youngest strata being the ones on top.
•Principle of Cross-cutting Relationships:
any structure (fold, fault, weathering surface, igneous rock intrusion, etc.) which cuts across or otherwise deforms strata is necessarily younger than the rocks and structures it cuts across or deforms.
Seek the peak FOSSIL SUCCESSION
Fossils show up in the geologic record in a definite , determinable and regular order . don’t present randomly
Any period of geologic time can be recognized by its fossil content
Example : age of mammals ( Cenozoic era )
So fossils can be used to identify the relative age of the layers of a rock formation .
so the organisms found in the top layers appeared after the organisms found in the layers below them .
Seek the peak Statigraphic terminology
Biostratigraphic Unit
Lithostratigraohicunit
Time stratigraphic unit
Rock content Fossil content Rocks of specific age
Seek the peak
Lithostratigraphic units
Based on Rock type with No consideration of time of formation or deposition.
The basic lithostratigraphic element is a formation can be subdivided
into members and beds .
Seek the peak
Lithostratigraphic units
It may consist of a single rock type Like sudr chalk ( frafra oasis )
Or a variety of rock types Like halal formation
Seek the peak
Biostratigraphic units
** A body of strata based only at its fossils content
* The main bio-stratigraphic unit is the biozone.
Seek the peak Time-stratigraphic Units
*Are the actual rocks formed or deposited during a specific time interval .
* called ( chrono-stratigraphic )
* The basic unit is the system
Seek the peak Time units
Eon Era Period Epoch Age
Common used
Time units are certain parts of geologic time .
Corresponds to the time – stratigraphic unit ( system )
Index Fossils M8
Are useful for correlation and the biostatigraphy.
To be a good index fossil, the species should:
1 ) Have been VERY common, so chances of individuals being buried is good.
2 ) Have hard parts, so chances of fossilization are good.
3 ) Have a wide geographic range, so that correlation over wide region is possible Lived in (or could be deposited in) different environments, so can be found in different formations.
useful for correlation. To be a good index fossil, the species should:
Index Fossils M8
4 ) Have some distinctive features, so it can be recognized from closely related forms.
5 ) Have a short geological duration (a few million years at most).
Index Fossils M8
1 ) Nannofossils
Are microscopic fossils (the remains of calcareous nannoplankton ) from various eras.
Nannofossils are very abundant, widely distributed geographically .
And time-specific, because of their high evolutionary rates.
Index Fossils M8
**** There are enormous numbers of useful nanofossils, including radiolarians and foraminifera.
**** Nanofossils are the primary method of dating marine sediments.
Seek the peak Index Fossils
Are extremely small objects (less than 25 microns) produced by planktonic unicellular algae .
Calcareous nannofossils
Seek the peak Index Fossils
Trilobites were common during the Paleozoic Era ( Cambrian age ) about half of the Paleozoic fossils are trilobites. ( common)
They extinct during the late Permian period.
Seek the peak Correlation
The process that use to understand the relationships between strata at different localities.
Seek the peak Correlation
1 - Which
layers are the same?
2 - Which is the oldest
Of the rock layers E and F ? And Why ?
Seek the peak Facies Fossils
Some fossils can be found only in certain environments , for long periods of geologic time.
They allow us to learn about the environmental conditions in the period when the covering layer was deposited.
Facies fossils M8
Example :
( lingula )A brachiopod living only in lagoonal mudflats .
It has changed very little in the last 500 million years.
Biozones M8
Biostratigraphy : Stratigraphy based on the fossil content .
Horizon : Is a specific layer vertical cross section .
Biozones- rock unit M8
Biozone (or "zone"): Rock unit characterized by one or more taxa that permit it to be distinguished from adjacent rocks.
Last Appearance Datum (LAD): either local or globalFirst Appearance Datum (FAD): either local or global
top related