According to thetidal hypothesis,big starorbiting around the sun finally approached It. A largemass of gas ejected from the sun due to the tidaleffect. In the course cooling, thetidal matter fragmented into small pieces forming planets, satellites,etc. As a result, the solar system was formed.

According to this hypothesis, the whole solar system including other heavenly bodies was in the form of nebula. Slowly. the nebula began to contract due to its own gravity and the outermost ring was detached from the central core, which start to revolve around the central core. This central mass become the sun and other revolving bodies became planet & satellites including earth.

The geological history is divided into four parts. They are:
-Precambrian era.
- Mesozoic era.
- Cenozoic era.

The largest duration of time of the geological time scale is called eon.
The second longest duration of time of the geological time scale is called era.
For example:Mesozoic era, Cenozoic era.

The duration of the Archean eon was from 4 billionyears agoto 2.5 billionyears ago.

The time duration of Paleozoic era was between570million years ago and 250millionyear ago.
Themain features of this era are:
-Sedimentary rocks were formed.
-Change in weather and atmosphere took place.
-Fossils of different plants and animals were formed.
-Aquatic & terrestrialvertebrate&invertebrate were formed.

Mesozoic era:
The time duration of this era was between (250-65)millionyears ago. A large number of reptiles were evolvedon the land and sea. So, this era was also known as thegolden era of reptiles. In the era, theclimate condition wassuitable for sustaining aquatic, terrestrial & aerialanimalslike dinosaurs, tortoises, toothed birds, etc.
Cenozoic era:
The time duration of this era is between (65-now) millionyears ago to now. In this ere, we human beings are evolved.The climatic condition...

Mesozoic era is called the era of creepers because in thisera, the climate condition was suitable to sustain aquatic,terrestrial and aerial animals like dinosaurs, tortoises,toothed birds, etc. In this era, evolution and extinctionof huge reptiles took place.

The dead bodies remains of animals and plants which areburied in the earth curst overlong period of timeare called fossils.
Due to natural disasters like volcano, earthquake, foods, etc. the plants & animals may sink into the earth's ground. The delicate parts of organisms decay in the soil while hard part remains pressed down in the ground. The external morphology of those hard parts is formed in the soil, sand, etc. in the form of all impression. In this way, fossils are formed.

Coal is a hard blaze minerals that is found below theground and is burnt to produce heat.
In ancient time, plants & animals were burnt underthe earth curst due to the different geological phenomalike earthquake, food, etc. Then the remainswere pressedunder high pressure and temperaturefor long time. When wholeor part of plant remains in swamp land in the form ofa fossils for a long time, it is changed to cool. In thisway coal isformed.
Its importance are:
- It is used as a fuel for railways,...

The oil that are formed in nature by the decompositionof parts of plants and animals that are burriedunderthe earth's surface for a long periodof time is calledmineraloil.
Any three importance of mineraloil are:
- It is used as fuel in vehicles, industries, etc.
- It is used for generating electricity, cooking, food, etc.
- It is used for making various types of chemicals.

The process by whichfossils are formed is calledfossilization. As we knowthat due to different naturaldisasters, the plants and animals may sink into theearth's ground. After that fossils are formed by theimpression of preserved parts and skeleton after theyare preserved by rocks. As a whole, this process iscalled fossilization.

a. Mesozoiceraand Cenozoic era.

Mesozoic era	Cenozoic era
It is the golden era of reptiles.	It is the golden era of human beings.
Formation of hills and mountains.	Breaking and expansion of rocks.
Coniferous plants were developed in this era.	Toothed animals, gymnosperms and angiosperm were developed in this era.

b. Paleozoic era and Mesozoic era.

Paleozoic era	Mesozoic era
Sedimentary rocks were formed in this era.	Evolution of dinosaurs took place in this era.
Change in...

In Mesozoic era, dinosaurs evolved andbecame extinct.

The fossils of dinosaurs is the evidence that there weredinosaurs on the earth in the past.

a. Evolution of fishes.
-Precambrican era
b. Evolution of horse.
-Cenozoic era
c. Evolution of monkeys.
-Cenozoic era
d. Dominance of reptiles.
-Mesozoic era
e. Evolution of fern.
-Paleozoic era
g. Development of conifers.
- Mesozoic era
h. Dominance of human beings.
-Cenozoic era

We all know that, the earth was evolved about us billions years ago.At the time of evolution of the earth, it wasveryhot and there was no suitable environmentfor the evolution and survival of living beings. So, therewere no life at the time of evolution of earth.

We all know that, in Mesozoic era,there was thedominance of various types of large reptiles likedinosaurs, turtles, etc. on land and marine water.So,Mesozoicera is called the era of creepers.

We all know that, petrol and diesel are formed whenthe dead plants and animals are burried under earth'ssurface and remainedfor long time there. It is formedby the process which is similar to fossilization. So,petrol and dieselare called fossilfuels.

We all know that, fossils are the remained parts ofdead animals that are burried long time ago under earth'ssurface. By studying the fossils, we can study aboutthe geological history. Like about the organisms evolvedbeforein past or age of something specific. So, study offossils is important for human beings.

We all know that, naturalgas burnscompletely without leaving anyresidue. It burns with a smokeless flameand doesn't cause air pollution. It doesn't produce anyharmfulchemicals onburning. It has high calorificvalue viz 55kg/g. So, natural gas is considered as good asfuel.