Tuesday, December 21, 2010

Geological Time Scale

Firstly the Calcium group analysis would be continued after January (hopefully) because I don't have any soft copy or rough hard copy of the discussion points since I sketched the person next to me to avoid falling asleep and falling from the stool, instead of taking notes.So all the notes are on the discussion of my record book, which cannot be moved out of the lab until all the lab sessions of the course are over.
:-)


Evolution of Cosmos

Universe began 15 billion years ago. 
Earth is 4.6 billion years old.
3.5 billion years ago life formed on Earth.
1.9 - 2 billion years ago Eukaryotic Cells appeared.
In the last 550 million years the evolution of most plants and animals familiar to us happened. 

Natural Effects

1) Meteorite impacts
2) Volcanic eruptions and Larva flows
3) Mountain building
4) Earthquakes
5) Erosion
6) Slow movement of continents
7) Formation and destruction of ocean basins
8) Glaciation (formation of sheets of ice)
9) Climatic Changes

Some of these do not happen today. But they have left records in rocks.

Some of these events have not occurred during the human life span. Such as 
a) Forming of large glacial ice sheets
b) Huge meteorite impacts
Other events have occurred too slowly, thus they are difficult to measure
a) Plate tectonics
- Sea floor spreading
- Continental drift
b) Erosion of mountain ranges
Some events are short lived but catastrophic
a) Volcanic Eruptions
b) Earthquakes
c) Floods

Fossils :  Fossils are preserved parts or impressions left by organisms (plants/animals) that lived in the past.
Fossil Records : The orderly sequence in which fossils appear within layers of sedimentary rocks that indicate  the passage of time
Study of fossils and fossil records are important in determining the events that occurred during each time interval/duration.
Sedimentary Rocks : Are formed from sedimentation of material at the surface of earth and settling of minerals withing bodies of water ,deposited in layers. These are the richest source of fossils.



Geological Time Scale

Geological time scale describes the timing and the relationships between events that had occurred during the history of the Earth. It is mainly based on major changes in fossil records found in rocks.It contains events that occurred during last 4.6 billion years.Geological Time Scale is divided to various time intervals of various sizes. The largest time intervals are Eons. Eons are divided into Eras,Eras to Periods and Periods to Epochs.

Eon  ~ Era ~ Period ~ Epoch




Animal Life Through Time


Life diversified in bursts /pulses.
Dramatic increases of diversity of life forms are followed by periods of low diversity.
Sudden increase of diversity is related to events such as ;
a) Development in hard skeleton marine animals
b) Development in flight in insects and birds
c)Transition to land
Sudden disappearances of large number of species within a short time (Extinction)


Precambrian Era


About 700 million years ago(mya) - multicellular organisms appeared
About 580 mya - first animal forms in the fossil records
Soft bodied animals (similar to jelly fish and annelid worms) evolved in the sea.
Continents were separate land masses.
543 mya fossil records show a sudden burst of many different life forms.
Diverse multi cellular animals appeared within short space of time (5-10my)
The ancestors of almost all the animals that live today are found in the fossil records of this era.

Paleozoic Era


Cambrian Period (543-505 mya)


"Cambrian Explosion"  ( the dramatic increase of diverse animal forms)
Development of hard body covering and spines on body.
Trilobites and worm like forms.
The climate was warm and the seas were shallow.
Primitive land plants that were associated with water appeared.
Towards the late Cambrian the appearance of fish like forms occurred.


Ordovician Period (505-440 mya)

Marine invertebrates specially Arthropods and Moluscs were dominant.
Great diversity of body plans.
Evolution of bones- a new tissue as a skeletal material occurred. First appeared externally.
The climate was warm.
Appearance of early Craniates.
Craniates have a bony structure called a skull in the head.
Craniates are Chordates
- Myxini -hagfish
-Petromyzontida -(including lamprays)
-Gnathostomata - (Jawed vertebrates)

Early Craniates 
                      Ostracoderms

Arose in the sea.
They were without Jaws.
Had circular, slit-like mouth.
No paired appendages.
Gill openings for respiration
Body covered with heavy body armour.
Several groups radiated extensively ( in large scale) during the Silurian and Devonian periods.
Two related specialized groups survive today.
a) Lamprays
b)Hagfishes


Sources :
Zoology notes 

Extra reading sources:

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