17.9
The pre-Cambrian/Vendian extinctions (500m BCE)
  
 
o Pre Cambrian period (4.6 billion to 523 million years ago)
o Vendian period (523-543 million years ago)
 
  The Pre Cambrian era was a period in Earth history before the evolution of hard-bodied and complex organisms. Throughout the extent of both periods, dominant Pre Cambrian and Vendian organisms were soft-bodied, simple, and entirely marine.  
  They swum around the water close to the surface of the immersed Earth, feeding of the very much stronger radiation from the Sun and the internal warmth of the Earth, still cooling down. Even at these Early stages there would have been land. Places where asteroids had smashed into the 100 metre deep ocean and created huge gaping holes and pockets of islands. But these few dotted islands of land were bare, warm, warped rock. Nothing yet lived on land. The diversification of life to hard-bodied organisms did not occur until the beginning of the Cambrian, when the first shelly fauna appeared.  
  About 650 million years ago, seventy percent of the dominant Pre cambrian life totally living in the oceans perished in the first great extinction. This extinction strongly affected stromatolites, acritarchs, and was also the predetermining factor that encouraged the diversification of the Vendian fauna that followed. However, pre Cambrian life totally in the oceans resembled modern-day soft-bodied organisms such as sea pens, jellyfish, and segmented worms that also perished in a second extinction event at the close of the Vendian.  
   
17.9.1 What happened then?  
  The impact of the asteroids had several effects. Firstly it fractured the Earths surface, releasing massive amounts of the inner core and creating volcanoes. Second, it twisted and re-shaped the Earths crust into mountain ranges, rather like the folding of a giant rug, when someone trips on the end.  
  The stretch of the Earth's crust could also accounts for secondary fissures at the other end, where another object hit, causing the crust to snap and thus create two or possibly three edges of a "mini" plate.  
  At this time, the temperature of the Earths oceans would have been incredibly het (possibly for over a year). Huge volcanic eruptions would have added to the massive amounts of dust particles creating thick, dense clouds in the Earth's atmosphere. Finally, the blanket of dust plummeted the Earth's surface into darkness.  
  Quickly the oceans cooled. Life that hadn't been boiled now faced the prospect of being snapped frozen. For the oceans quickly began freezing up, all across the globe. A massive ice age occurred where the entire globe was covered in ice for years.  
  The life most likely to have survived the heat wave of the oceans, closer to the poles now face being the first to freeze to death. They may have got half way, say around where Europe now is located and the early islands that may have eventually become Australia. And there- the miracle of snap freezing took place.  
  Life, growing the conditions for growing ceased to be possible. But life was not dead. It was frozen in the frozen oceans of the globe.  
  As the dust gradually settled, the sunlight started to break through again and the oceans thawed after several thousands of years. During this period, the floor of the oceans were scowled by the giant glacier. Ridges and mountains were warped even higher, crushed by the expanded massive ice pack.  
17.9.2 The signature pattern of life  
  But we also see from the extinction, that life through DNA understood the conditions and the need to adapt to possible future changes. From now on, life had to adapt with harder bodies. Harder bodies could withstand the greater changes of heat and cold. It certainly the reason that we see basic organisms develop into shelly types during the next period, apart from the continuation of soft bodied creatures.  
     
 
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