Dinosaurs, conifers and flowering plants.
The opening of the Atlantic...

Timeline 4 - 250 million years ago to present
www.fsnielsen.com - return to graphic - previous - next -  The great event in this period is undoubtedly the opening up the Atlantic Ocean - a slow process, that is still going on, starting, perhaps, with initial conditions not dissimilar to those at present obtaining in the Rift Valley in East Africa. It was the visible correspondence of the American and Eurafrican continental borders that supplied Alfred Wegener with his first clue to the theory of continental drift, which he proposed in 1915. Though considered ridiculous at the time, it is today unanimously accepted by geologists and geophysicists. Later research has shown that the opening of the Atlantic was only a part of a far larger and more impressive global process - the breakup of the supercontinent Pangea:	Africa, Europe, and North and South America, before the opening of the Atlantic Ocean (ca. 200 mill. years ago)

It is on this background that the other events of this period must be seen: A single, continental mass, with its vast, dry and cold interior expanses, was supplanted by many, spread-out island continents, with wetter and more varied climates. The rifting process also led to a parting of ways for many species of flora and fauna, particularly in the Sounthern hemisphere, which from now on developed in disperate ways on the South American, African and Australian continental isolates.

The period opens with the next to last Great Extinction before our time, which killed off (among countless other species) the trilobytes, but left the scenes open for an explosive development of reptiles into giant reptiles: dinosaurs. Dinosaurs "reigned the world" for some 130 million years, until the next (and as we speak last) Great Extinction in global history, when they were killed off.

Towards the end of the period we see a world forming that is populated by more familiar species: conifers, flowers, birds, mammals. The two latter groups emerged only after the last great extinction, and seem yet another proof that these events have indeed stimulated biological diversification. As we shall see, a similar role may be played by the smaller extinctions caused by ice-ages in recent years.

Towards the end of the period we also see the buildup to the last great mountain-folding process in global history: this was when all "modern" mountains arose - the Alps and the Himalayas, the South American Sierras and the North American Rockies. And with more mountains come colder weather again.

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