Did you know #65| Origins of life
The first life on earth appeared not on land, but in the ocean. The atmosphere was thin at that time. There was no enough oxygen to sustain life. Ultra-violet radiation was at dangerous level. These problems were not there under water.
Life probably arose about 3800 million years ago. No one knows how life began. The scientists think that shallow, warm water - pools at the edge of oceans provided the ideal place for the origin of life. Chemicals were formed and chemical reactions took place due to lightening (3800 million years ago).
The earliest life forms were bacteria. Later, around 580 million years ago, the first sea creatures were born. Until about 450 millio years ago, there was no life on land. Gradually, the algae" in the water may have been washed ashore. Thus plant life began on earth. Land plants were a good food source. So, some marine animals evolved to take advantage of it. Insects and spiders became the first land animals.
Then plants spread across the world. Big trees grew. At this stage, about 350 million years ago, the amphibians were born. These amphibians learnt to live on land. Then they became reptiles. The reptiles became extinct about 250 million years ago. But the reason for that is not clear. However, a number of reptiles survived. They developed the ability to moved around on two legs. They were the first dinosaurs.
By about 65 million years ago, all the dinosaurs Were extinct. During this period, several different groups of mammals were evolved around the World. These mammals - a much higher form of animal life - still dominate the animal kingdom.
1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54,55,56,57,58,59,60,61,62,63,64