HOW DID LIFE BEGIN ON THE EARTH?

     At first we must know about our solar    system. Our solar system has been situated in Milky way  which is our galaxy. There are a lot  of galaxies and they all contain numbers of   solar systems just like ours milky way. One interesting fact is that all galaxies does have their own gravitational force and that all are held together by that gravitational force.  Just like galaxies, all planets which are situated in that different galaxies also have gravitational force and that force is responsible for the movement of planet's in there particular orbits around the sun. Sun is the centre of our solar system just like centre of any atom and other planets are moving around the sun just like electrons but in our solar system single orbit contain only one planet. 

That all planet's have there different gravitational force. Ther are 8 planets in our solar system which have gravity and Jupiter have more gravity than other remaining seven planets because gravitational force is directly proportional to mass of that particular planet and jupiter is biggest planet in our solar system. For ex. Size of earth is to much small as   compare to the Jupiter that is why     gravitational force of Jupiter (24.79 m/ s2 ) is more than earth ( 9.807 m/ s2 ). Gravity is the force by which planets or body attracts objects  to their centre. All that 8 planets have been exerting that force on each other since the the creation of solar system eventhough they  are not getting attracted by each other instead of that they all are getting attacted by sun. Sun is the centre of our solar system. And sun has largest mass means greater gravity than other  all 8 planets. that sun gravitational force is the thing that keeps all 8 planets revolving in their particular orbits instead of collides on each other as well as on sun. According to some geologist process of creation of earth had been started almost 4.5 billions years ago. That all could happen just because of gravitational   force. At first there was just sun and countless rocks called stars and dust were floating in our solar system. That stars was continuously colliding on each other due to that collision   they converted in to small pieces of rocks and dust. That's where gravity played their major role. 

Because anything that has mass also has gravity. 

Those rocks and dust had mass means they had gravity that is why that all particles started to gathered together. everything was happening    at small scale, Years by years that young planet was growing. Over millions of years gravity    was gathering that small particles together.    that time the young planet earth was just like boul of lava temperature of that was approaching 2000 fahrenheit.

 There was no any single chance for life to grow because there was no atmosphere which we livingspecies need to survive. There was just carbon, hydrogen, nitrogen, and And that time earth was spinning to much fast and day time was just about 6 hours long. But then 3900 billion's year ago Started heavy fall of meteoroids on young earth may be that meteoroids was created  due to the formation    of our solar system, 

because that time our earth was not only one planet who was getting create but also whole solar system was getting create. may be that   was the turning point for creation of water on earth. According to scientist,  geologist predictions that meteoroids was containing water molecules each of them was containing negligible amounts of water. But bombardment of that meteoroids for 20 millions years was sufficient period to covered whole earth surface with water. But there was just water but no surface. But then something was going to  happen and that was volcanoes, they started to pumping out hot lava and that's how small islands created on the earth 

But eventhough life was impossible on the  earth. but then 3800 billions years ago again started the bombardment of meteoroids but   this time they were containing carbon and protiens of amino acids Instead of water molecules. That meteoroids felled in water and dissolved and volcanoes were alive in water   and they were realeasing some important nutrients in water as well. Because volcanoes contain different types of melted rocks like calcium carbonate, phosphate and other nutrient which are important for life   generation so that's how sea water became   boul of nutrient and first time microscopic single cell bacteria born on the the earth. Then 3500 billions years ago in ocean bacteria called stromatolite born. 

they still are on the earth they just look like   rock but stromatolite was able for formation    of food by using carbon dioxide and water with the help of sunlight called photosynthesis process. As we know biproduct of this process    is oxygen. That's why water of ocean became rich of oxygen. And then that oxygen reacted with iron present in ocean water and    converted that into rusted iron which settled at the bottom of oceans in form of iron rich rocks. Now we are using that iron for different types   of purposes. Just because of sromatolite     oxygen level of atmosphere was increasing. Stromatolite did create a very important   element for the life otherwise life would not have exist on the earth. In next 2 billions years oxygen level on earth increased  tremendously and spinning rate of earth got reduced as well,   in result day on earth became about 16 hours. And then according to geologist 1.5 billions year ago earth surface started to break by earthquakes and all small small islands came close to each other and formed mighty continents. Just because of stromatolites oxygen level of earth was increasing years by years for almost 2 billions years in result temperature of earth became almost 80 - 85 degree centigrade. But Still life was impossible on earth. Then  again 750 millions years ago earth surface started to break and that is how that mighty continent split into the small continents. Due to the surface breaking process, 

volcanoes woke up again and started pumping carbon dioxide and sulfur dioxide in air that carbon dioxide was getting mixed with water  for millions years, in result acid rain started to fall that process was carrying out for millions years. During that period rocky surface of earth of was absorbing that acid rain water and carbon dioxide which was present in the air. In result carbon dioxide in earth atmosphere got reduced and wasn't enough to trap sunlight or hold heat that's why earth temperature fell down. Then 650 millions years ago whole earth got frozen by ice.

   Earth was frozen for almost  15 millions years. But that wasn't end of the earth. Because there was something in the core of earth ' lava " volcanoes played their magical role in survival of life and earth. Volcanoes again started pumping carbon dioxide in earth atmosphere, last time there was rocks who had absorbed carbon dioxide but this time they all were covered by thick layer of ice, that's why whole atmosphere of earth again full filled with  carbon dioxide and then ice started to melt.

 Through the chain of chemical reactions ice created oxygen. While earth was frozen ultra violent radiation from sun reacted with frozen water molecules in ice and produced hydrogen peroxide. Due to increasing temperature of  earth that frozen hydrogen peroxide started to break and released massive amount of oxygen. and that's how earth atmospheres again   became rich of oxygen. 600 millions years ago fisrt time earth temperature became a normal like summer. And day time became about 22 hours long. Now 540 millions years ago Ocean water was rich of oxygen and that is why again that primitive bacteria started to evolve. But   this time something was special . life had  started to evolve from microscopic bacteria to big species in oceans. This time there was water living green plants like alga and others, the creatures who can migrate from one place to another like worms, sponges, trilobites others. 

Trilobites 

Worm                                                                               

Sponges 

Increased oxygen level was allowing them to grow more bigger and bigger. That's how life started to grow in the oceans. But 450 millions years ago on the land  there were a lot of places where oxygen level was just like now on the earth eventhough there was no sign of life,   there was only one reason behind that and    that was continuous emittion of ultraviolet radiation by sun but now oxygen level in earth atmosphere was increasing. And as we know when oxygen react with ultraviolet radiation, magical gas called ozone forms. That ozone gas created a protective layer around the whole world, that layer was getting thicker for 120 millions years. And eventually it became  enough thick to  protect living species on the land from harmful radioactive radiation which comes from sun and made perfect weather for the formation of life. Whithout ozone layer life on earth wouldn't have existed. Then plants started to grow on earth surface. In upcoming years whole earth filled with green  plants.

 They were also producing oxygen that Is why earth oxygen level was increasing more years  by years. Then after few millions years water living creatures somehow managed to survive on earth surface that's how new lifes started to grow on earth surface. That creature's were big because of high oxygen level and trees size was also big as compared to now. After completing their life span trees started to die and that all thousands of died trees got buried in ground    for millions years. Due to the underground pressure that all died trees wood converted into coal that we are using now as fuel.

 Everything was going well but then volcanoes woke up again and again big disaster happened. Volcanoes started pulling out large amounts of carbon dioxide and sulfur dioxide that is why atmosphere of earth again filled with that toxic gases, earth gone in darkness, that sulfur  dioxide reacted with water molecules and acid rain of sulphuric acid started to fall. That is why all living species extincted from the earth. Oceans became pink because of sulphuric acid and all marine life wipe out from the earth.   That all died Marin lifes settled at the bottom    of oceans and after millions of years they all    got buried in the bottom of oceans just because of unground pressure died fishes and all other creatures transform into oil.

 That we are using as fuel. For another millions years there was no sign of life on earth. But again magic happened and earth atmosphere became clear and neutral, but it tooks millions years. And 200 millions years ago again life started. But this time giants dinosaurs was the members of this earth. 

There was no any other species who can defeat them that's why they dominated the earth for almost 160 millions years. They could have survived for few more millions years but 65 millions years ago something was coming toward the earth with 40000 thousand miles   per hour. And that was giants space rock, it fell on the earth with mighty impact. it was just like explosion of millions nuclear bombs at the   same time. Due to that  whole earth   atmosphere again filled with smoke and dust.    it was impossible for sunlight to reach on earth and trees started to die and dinosaurs also died because of poisonous smoke and dust atmosphere. 

But now it was big opportunity for the our ancestor the mammals to evolve. They    survived from that disaster by living underground. Thats how they  managed to   avoid burn by exceed hot atmosphere. 47 millions years ago there was peace on earth    and our ancestors were evolving years by   years. Temperature was 45 degree centigrade and day was about 24 hours long just like now. Now 4 millions years ago apes started evolve. It tooks millions years to brought them on land from the trees and eventually  75 thousand  years ago they evolved into smart species called homo sapiens. 

That is how our  human species  journey began.