The Extinctions and Marine Life (20-01-2009)

Most of us are aware of the fact that life started in the sea. Early simple forms of life turned complex over time and eventually the fish evolved. Later they gave way to marine reptiles and soon to giant marine mammals. During this long passage of evolution, there were five major extinctions. Perhaps, we, the highest life forms may be responsible for the sixth.

It is thought that Mother Earth is approximately 4.5 billion years old. We have come to the conclusion that life started to evolve about 3.5 billion years ago under the sea. Obviously the first organisms to breathe air were single celled similar to modern bacteria, with true cells evolving about 2 billion years ago. Scientists predict many natural evolutionary experiments took place, and most of the weird creatures that were fossilized came from this period in time.

Here’s a list of extinctions that drastically altered our planet:
1. 443 million years ago: Early invertebrates wiped out.
2. 368 million years ago: Only 20% of marine families remained.
3. 252 million years ago: More than half the animals wiped out.
4. 200 million years ago: The end of the very successful ammonites.
5. 65 million years ago: The end of most marine reptiles, and dinosaurs on land.

We may provide the sixth extinction!

Between 418-354 million years ago, fish were recognized as the highest life forms in the sea. Now, they are no gold fish. Many of them were large armored beings with four fins! The coelacanths from this period are the ancestors of amphibians and reptiles. 250 million years ago, the sea was re-colonized by the land reptiles. And they were quite successful until the last extinction took them out with the dinosaurs.

They reigned the oceans as the top predators for 200 million years, and the ichthyosaur behaved like the dolphins do today. Mammals started to evolve on land after the dinosaurs and marine reptiles were wiped out. Approximately 50 million years ago, some of these land mammals went back to the sea, and the first of the whales started to appear. After 14 millions years, the ancestors of marine mammals like dugongs and seals joined them. In this day and age, sharks and some coelacanths have still remained since the age of fish, and of course the turtles remained from the age of reptiles. Well, it may be only a matter of time before such life forms will disappear as well. Natural phenomena caused all five previous extinctions. Let’s hope human activity won’t turn into the next cause.



wayne's tip!!
 naver, daum 등에서 제공하는 툴바(toolbar)를 설치하면,
마우스 포인터를 단어에 놓기만 해도 그 뜻이 나와요.
단어를 찾는 시간을 많이 줄일 수 있답니다! ^^