Continental Drift and Evolution

What, Where, and When

Plate tectonics and continental drift are “computer-age” theories. Using computers, the best fit of the shapes of the continents was determined, and the shapes were moved around based on current rates of continental movement (5 to 10 cm/yr). The results have then been compared with existing fossils and other geological evidence.

Ocean Until about 500 to 425 million years ago (mya), all organisms were aquatic, including simple algae, fungi, several phyla of invertebrates, and a few vertebrates such as fish.

420 mya Around 500 to 425 mya, the first land-dwelling organisms appeared, including simple plants and arthropods. At that time, there were a couple major continents, and the area that included what is now the Atlantic coast of North America and the hump of Africa (which were joined together) was over the South Pole. Later, this land mass gradually shifted northward on “our” side of the Earth as the continents approached each other.

360 mya About 360 to 340 mya, during the Paleozoic Era, there were two major continents. One, called Gondwana, included what is now Africa, South America, Australia, Antarctica, and India. The other included North America and much of what is now Eurasia. The climate on the North America-Eurasia continent was equatorial and warm, and the main biomes were swamps and/or tropical rainforests. There were many amphibians, as well as insects, spiders, and other arthropods.

Tree Fern Vegetation included a variety of ferns and large tree-like relatives of present-day Lycopodium. These organisms were able to spread throughout this continent anywhere it was warm enough, thus their descendants may be seen throughout present-day North America and Eurasia. Subsequent climactic changes killed large numbers of organisms, which now are the coal that is mined here in North America and in England.

240 mya Approximately 280 mya, Africa and the Atlantic coast of North America “collided,” and the pressure of Africa on North America caused the Appalachian Mountains to be formed. Geologically, the Appalachians are much older than the Rockies, thus are considerably more worn down. Similarly, a collision of Europe and Asia caused the Ural Mountains (a north-south mountain range in the middle of Russia) to be formed.

Smoky Mountains

Pangea 180 mya By about 180 mya, nearly all the land was pretty much united in one large continent called Pangea, and thus, all the water was in one large ocean called Panthalassa. This time period is the Jurassic Period of the Mesozoic Era, and has been nicknamed the “age of dinosaurs” because of their prominence. In addition to dinosaurs, there were many species of cockroaches, other reptiles, and gymnosperms including conifers and cycads.

Cycad It is thought that the very first birds and mammals appeared near the end of this time period. Because the land mass was all united and organisms could spread anywhere on it that provided a suitable habitat, life forms or their ancestors present at that time are represented on all present continents, whereas types of organisms that appeared later (after the break-up pf Pangea) are only found certain places.

Cockroaches

120 mya Sometime between 180 and 120 mya, Pangea started to break apart. The northern continent formed from this was called Laurasia and consisted of what are now North America, Greenland, Europe, and Asia. Gondwana, the southern continent, was made up of South America, Africa, Australia, India, and Antarctica. The climate included warm, tropical and subtropical areas. Because of the warmth, the oceans were high and covered much of the land, limiting movement. During this time, angiosperms, mammals, birds, appeared.

Marsupial About 120 mya, Gondwana broke into three pieces, including South America/Africa, India, and Australia/Antarctica. At this time, India started going its own way. Initially, the tip of South America was very close to Antarctica. As this split was occurring, the first marsupials evolved on Laurasia and spread south to Gondwana as the split was occurring. When the marsupials spread as far as the south end of South America, there was still a land bridge between South America and the Antarctica/Australia continent, so marsupials were able to spread to the Antarctica/Australia continent. As the climate changed and became a little cooler, the dinosaurs declined.

At about 100 mya, South America and Africa split.

Goat Some time in here, placental mammals also arose on Laurasia, and subsequently spread to South America, Africa, and India when those crashed into the northern continent(s). However, by the time the placentals spread to the south end of South America, there was no longer a bridge to Antarctica/Australia, so the placental mammals couldn't get there. This is significant because, wherever placentals went, they out-competed the marsupials (meaning natural selection/more fit, not that they got into fights!) and marsupials, except opossums died off.

60 mya Around 60 to 50 mya, Laurasia split into North America, Greenland, and Eurasia. Again, just prior to this split, Laurasia was the site of evolution of the placental mammals which moved south, out-competing the marsupials. Between then and now, Africa and Saudi Arabia collided with Eurasia and India collided with Asia forming the Himalayan Mountains. Thus mammals from Eurasia could spread to those places. North and South America touched and a land bridge formed across the isthmus of Panama. More recently evolved plants and animals could use these new land bridges to migrate to areas formerly separated by ocean. However, it is important to note that none of them could reach the Antarctica/Australia continent.

Tasmanian Devils Eventually, Australia and Antarctica split from each other. Antarctica went to the South Pole and became too cold, killing all the mammals (marsupials) present there. Australia went north to near the equator, and its marsupials thrived. With no competition from placentals. Australian marsupials evolved/diversified to fill all the niches filled by placentals elsewhere: kangaroo are grazers like cattle, koalas eat tree leaves like giraffes, marsupial dogs and Tasmanian devils are predators.

0 mya The ice ages occurred about 2 mya. Ice sheets and glaciers separated populations of organisms which, being then in different habitats, had different selective pressures acting on their alleles and thus evolved into different species. This has resulted in the large variety/number of species we see today we see today, especially in “northern” genera.


Continental Drift

Continental Drift Here is an animation of the process of continental drift. Note that the images will change somewhat slowly to allow you to view each one. Click on the animation to re-start it.



Copyright © 1999 by J. Stein Carter. All rights reserved.
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