age of earth

                                            Age of earth

                                                                                                                                  :- Many philosophers have speculated on the age of earth & their estimate vary from one another in a great range.

The age of the earth has been determined from

 a) Evidence from the evolutionary changes of animals. 

 b) Evidence from the rate of formation of sedimentary rocks i. e. average rate of deposition, thickness of sediment in oceans.

c) Evidence from salinity of sea water.

d) Evidence from rate of cooling of the earth.

e) Evidence from disintegration of radioactive elements. This is modern method of determining age of earth.

The earth is an continuous state of change. The total amount of changes as for produced & the rate of changes are calculated.Then it is possible to determine the age of earth by formula.

      Age of earth =         Total amount of changes   /     Rate of changes.

Since the beginning of 19^th century the attempts were made to solve the problem of age of earth. On the scientific  basis  following are the methods.

1)    Physical method.                     2) Geological method.

 3) Astronomical method.           4)  Chemical method.  

1) Physical Method: - Hord Kelvin, the great English physicist regarded that earth is loosing heat & getting cooler the age of earth determined 20 – 40 M. yr.

2) Geological Method:-

 a) Sodium deposit in sea. Total salt of sea 3.5 % by wt. 75 % of salt is Na. Total amount of Na in it 16 x 10¹⁵. The annual increment through being river is of order of 16x107 tones. 10 million yrs.

 Many serious objections are:-

1) Annual rate of addition of Na may not be uniform.

 2)  All Na may not be in dissolved state.

b) Sedimentation: - Varred sediments, homglass method. Sir Geikie determined the age of earth by calculating the thickness of geological formation are dividing the result by assuming rate of the deposition of sediment. But this is an unreliable method because of rate of sedimentation extremely variable.

c) Biological Evolution Method: - This method is still vaguer & often to criticism that other organisms have evolved from simplest to animal cules to present state.  

3) Astronomical Method: - According to Jeffery all planets are of same age this method is based on ocentric the orbit of planet mercury.

4) Chemical Method: - This method is most reliable since they are based upon the changes & unaffected by the temp. & pressure, radio active etc. The radioactive elements have remarkable properties of self disintegration ultimately resulting in new stable element.

The principle radioactive isotopes are U²³⁸ ,   U²³⁵ ,   Th²³²  ,    Pb ⁸⁷ , K⁴⁰   Pb²⁰⁶   Ar⁴⁰  Sr⁸⁷

Half life is the time taken by radioactive element to decay it’s half the amount.

1)    Helium Method: - U²³⁸ -------------à  Ra²²⁶  + 3He .            One gram of                                                          uranium gives one ccs of the He in 8.8

2)    Lead Method: - Uranium – lead ratio is more accurate than uranium – Helium.

                                    U²³⁸ -----------à Ra²²⁶  + 3 He⁴ ------------à Pb²⁰⁶  + 8 He ⁴

One gram of uranium gives 1 c c lead in 7600 mg.

3)    Alkali Method :-                           |---------- Ca ⁴⁰

                                                  K ⁴⁰    ---à|

                                                                    |----------   Ar ⁴⁰ 

Age of earth is 4550 million yrs.

4)    Radioactive Method: - Radioactive dating is the determination of age of radioactive carbon. This method has got great over other method.

 Radioactive C ¹⁴ is formed is the atmosphere by collision of cosmic rays (neutron) with atoms of Nitrogen N ¹⁴. In turn each C ¹⁴ nucleus losses a β particle. Α is transformed back into N¹⁴ the rate of decay is such that the half life is 5570 yrs.

earthquakes(1)

 Geological consideration for choosing sites of building in seismic areas.

Damages to structure because of earthquake can be reduced or even prevented by properly siting the structure with respect to geological conditions & by suitably designing them.

1)    Building should be founded on hard bed rock. Building situated on river alluvium , steep slopes always suffer more in an earthquake. These situations should be avoided.

2)    Simple rigid structure stands up well against vibration. All parts of a building should therefore well tied together so that the whole structure react to vibration as a unit. Foundation also must be so designed that the whole structure vibrates as a single unit. For large building raft type foundation are advisable. Building with irregular shapes & tall structure should be avoided.

3)     If the period of vibration of a structure is the same as that of the foundation rock it will collapse because of resonance. Therefore the types of building on each type of rock must be so chosen as to avoid resonance.

4)    Provision has to be made in the design of structure to guard against acceleration produced by earthquake. Areas like the Indian peninsula it is common practice to adopt a factor as low as possible for economic point of view.

Geological Effects :-                                                                                                                                      1) Minor faulting takes place.                                                                                                     

  2) Course of river may change.

3) Waterfall may create.                                                                                                       

 4) Groundwater level may rise or down in well.                                                

  5] Some of well may dry.                                                                                                         

6) Landslides may takes place.                                                                             

  7] Tsunami, [great tidal waves] are generate which often do greater damage on   coast.

Earthquake in regions of dams :- An earthquake is a 100 % geological phenomenon & any connection  both dam & earthquake has to be proved on the basis of geological evidence , but no geological evidence has been produced to show a dam has caused an earthquake.

Hence as no cause & effect relationship has been established between dam & earthquake & there is no justification for maintaining that dam cause earthquake.Koyana earthquake 1967.

  

Earthquakes

                                           Earthquakes

Definition: - Earthquakes are caused by the passage of vibrations set up in rock body.

There are two types of earthquake. 

1) Volcanic earthquake: - Due to volcanic eruption – it effect local in nature.

2) Tectonic Earthquake: - It is due to earth movement (orogenic & Epiorogenic). It held very longer distance.

Earthquake waves: -

 During the formation of tectonic earthquake the energy is released in the form of waves, which are called as earthquake waves. It is also called seismic waves.

a)     P- Waves :- (primary waves):-These are push or pull waves. These waves are longitudinal in nature & travel with very high velocity. P-waves can passes through solids , liquids & gases.

b)    S-Waves:- (secondary waves ) These are transverse in nature & their velocity is less than P-waves . S-waves can passes through solid & gasses, while in liquid media they are reflected.

c)     L- waves:- ( long waves) These waves are also transverse in nature & their velocity is less than P & S – waves. These are also called as surface waves because their journey is limited to the surface of the earth only.

 

Focus: - The place at which an earthquake originate called it’s origin or focus. The deeper, the focus, wider is the felt area.

Epicentre: - The point on the surface vertically above the focus is known as epicenter of earthquake. The intensity felt at the epicenter is maximum.

Isoseismal Lines: - The lines joining the point of equal earthquake intensity are called isoseismal lines. They may be either circular or irregular in shape. The instrument used for recording earthquake vibration is called seismograph. The scale used to measure magnitude of earthquake is Richter scale.

physiographic division of india(4)

RED TACHYLATIC  BASALT

 By hydrothermal alteration the black colur of the fresh tachylytic basalt is changed to red and hydrothermally altered red tacylytic basalt are much more common than unaltered black tachylytic basalt.

If Red Tachylatic  basalt  confined condition i. e. below the cover of rock then it is very hard compact suitable for any foundation.

If Red Tachylatic  basalt  unconfined condition i. e. exposed to atmosphere it decompose weather very fast & to get friable loose material is called Red bole. (Soil)

 Engg. Point of view it must be below the cover of rock.

Dykes in Deccan Trap: - Over large areas the D. T. Lava have been intruded by basaltic dolerite dykes. They are numerous in Tapi & Narmada valley. Saurashtra, North konkan , Dhule Jalgaon. Few dykes in Pune, Nasik, Ahemadnagar, Jalana , Aurangabad dist. Most dykes have a considerable lateral extent about tens of km. Their thickness varies from half meter to 50 m.

Dykes having prismatic joints due to which if joints open wide & inter connected leakage may occur in foundation of structure .It may required to excavate , grouting & back filling impervious material along trench of dyke . Most of the dams in Maharashtra crossing no. of dykes very few are leaky.

Inter-Trappean beds.:- Deccan trap formation are made up of basaltic flow . These basaltic flow were not erupted continuously but in between two successive basaltic flow there is long time internal gap. During this time gap between two flows there was presence of some fresh water lakes. Due to which there was river origin deposit. These deposits are very few in lateral extent & their thickness varies from 3’ to 10’. It contains plant and animal fossil. Deposit in both two flows are called Inter trappean beds. Composition  may be chert, impure lime stone, clay. Many plant remains & fresh water mollusca, shells are well preserved .Similarly the fossils of frog , fishes are found. Such deposit occurs near Malbar hill, Worli, Nagpur, Dhule etc.

physiographic divisions of india(3)

 Field characters of Deccan trap basalt flows.

The field characters of the basalt flow such as thickness , lateral extent , and form with absence or presences of gas cavities . compact and amygdaloidal basalt have different field characters.

1)    COMPACT BASALT- It occurs as thick, extensive flows , by regular tabular form and top and bottom to parallel plane surfaces  lateral extent up to 20 km, thickness is 45to 70m.

Engineering significance –  1) Heart and bottom portions

      Well jointed, therefore deep weathering and deeper foundation , possibility of leakage below the dam and hence treatment is necessary.

 2)Top portion of the flow – Some thickness of the top portion may become vesicular amygdaloidal and hydrothermally altered  hence un jointed , therefore suitable from dam foundation and tunneling point of view.

 2)AMYGDALOIDAL BASALT-Shows much variation in field characters

1)    a) Plane amygdaloidal basalt - It occurs as flows , by regular tabular form and top and bottom to parallel plane surfaces  lateral extent up to 1 km, thickness is up to 10m. Un jointed

2)    Thin irregular amygdaloidal basalt - It occurs as flows , by irregular form and top and bottom  not parallel plane surfaces  lateral extent up to 40m, thickness is up to 1.5m. Un jointed

3)    Thick irregular amygdaloidal basalt - It occurs as flows , by irregular form and top and bottom  not parallel plane surfaces  lateral extent up to 400m, thickness is up to  6m. Un jointed

Engineering significance-Fresh amygdaloidal basalt are always un jointed . Vesicules in them are either filled by secondary minerals  or even if unfilled . They are not interconnected  therefore they are suitable for dam foundation and for tunneling. Excellent construction material as rubble for masonry metal for concrete and as a substitute for sand after crushing.

physiographic division of india(2)

5.     Gondawana System. : -                                                                                     

a) Introduction --   After the deposition of Vindhyan system there was a great period of non-deposition in the stratigraphy of peninsula.

·        The name Gondawana comes from area of south of Narmada by the Gondas were first studied.

·         It is made of deposition in the slowly sinking faulted trough.      

·         B]Distribution :- 1. A large tract in West Bengal along Damodar valley & Rajmahal hills  2. along Mahanadi Valley  3. Along Godawari River & Penganga near Nagpur        4 .Cutch, Rajasthan, Saurashtra, Wardha, Yeotmal, Nagpur, Chandrapur        district of Maharashtra.

Classification:-                

          Upper Gondwana                                Umia                                        fossil

                                                                        Jabalpur                 tlyllophyllum flora

          Middle Gondwana                                 Rajmahal                Da crodium flora

                                                                        Mahadev

                                                                        Panchet

         Lower Gondwana                                    Damuda                   Raniganj [coal]

                                                                                                           Barren measure  

                                                                                                             Barakar [coal]

                                                                                                            Karharbari

                                                                        

                                                                                     Glossoptris & gongamopteris                                                                

                                                                            Talchir  

                                    

b)     Lithology: - Shale, sandstone, conglomerate, coal seam, intrusion of dolerite dyke.

c)     Age: - Carboniferous to Jurassic.                                                                                

d)     Indian coal: - The economic importance of the Gondwana is that they are the major source of coal in India. 80% of all coal comes from lower Gondwana [Damuda] i.e. both in the Barakar & Raniganj series.

 The important coal fields in India are

1.     Raniganj coal field.       2. Jhariya coal field.       3. Bokaro coal field.

      4.  Rampura coal field.        5. Singareni coal field.     6. Giridih coal field.

Coal field in Maharashtra: -     1. Kamtee coal field.      2. Bokaro coal field.

     3.Umrer coal field.          4  Wardha coal field. 5 Ballarpur coal field

6   Ghuhus coal field  7 Rajura coal field 8 Worora coal field

6. Deccan Trap :-                                                                                                        

 a) Introduction: -    At close of cretaceous period, large part of peninsula was affected by volcanic activity. This result into a thick series of lava  pyroclastic  material. Eruption of magma through  fissures.  Such type of eruption is called fissure type of  eruption .These flows are horizontal, they look like flat plateau & their composition  is basaltic so they are called plateau basalt. They are called Deccan trap because of their step like appearance.

b) Distribution: - 85% of area of Maharashtra & wide area of M. P., Gujarat, A. P., Karnataka. Maximum thickness of lava 3000 mt.

c) Lithology: - Plagioclase Augite basalt, Vesicular, compact, Amygdaloidal basalt, Trachyte, Rhyolite, Andesite  ,diorite gabbro.

d) Types of basalt:-                                                                                                                    

1) Giant phenocryst Basalt. (2 to 10 cm)  length of plagioclase.

2) Compact Aphanitic Basalt.      

 3) Hydrothermal altered Basalt.

4) Amygdaloidal Basalt with large amygdales.

 5) Amygdaloidal Basalt with medium amygdales.   

 6) Amygdaloidal Basalt with small amygdales.

 7) Amygdaloidal Basalt with pipe amygdales.

8) Vesicular Basalt.   

9) Porphyritic Basalt. 

10) Tachylytic Basalt (Red, green, black).

11) Red Tachylytic Basalt.

 12) Volcanic breccias

 13)  Volcanic breccias with gray lava matrix.

14) Volcanic breccias with R.T.B.  

 15) Volcanic breccias with Zeolite matrix.