The Extinction Of Dinosaurs Helped Us!!

 The extinction of dinosaurs was actually one of the reasons we are here. Can't believe it? Let's elaborate, the first notable multicellular creatures on earth were various kinds of fish that lived in water. But, after some time food became scarce in water, so some fish evolved and started growing limbs to become 'amphibians.' amphibians were the first creatures to walk on land. But they had to live near water to prevent drying up of their skin. this led to another mass evolution where some amphibians evolved into creatures with dry skin and fully terrestrial creatures: these were the reptiles. Point to be noted that all of the above-mentioned creatures are cold-blooded. As reptiles were the most successful animals until that point in time, they ruled the whole planet at that time. T-Rex on land, Elasmosaurus in water pteranodon in the air: all were rulers of their terrain. 

But as everything has a beginning, a middle and an End, Dinosaurs were wiped out from the face of the earth, not by any other dominant animal, nor by any natural disaster, but by an extraterrestrial disaster. an asteroid impact shook the whole planet and wiping out 75% of living species. 

 This was the point of time when mammals got a chance to evolve. Point to be noted that mammals actually coexisted with dinosaurs for about 150 million years! But as dinosaurs were much more dominant, mammals could not even evolve properly. But, now as dinosaurs were gone, mammals grabbed the chance to rule the earth and evolved into much bigger species. So, these mammals then evolved into Primates and ultimately, we humans. 

We could call this a chain reaction, where even if one link is broken,(here, it is the extinction of dinosaurs) the whole chain gets scrambled.