Elaine Meinel Supkis
The formation of rift valleys coupled with landmasses splitting off from each other are the engine for rapid change in ecosystems. Today, with humans reuniting even the most isolated parts of the earth, carrying biomatter from all parts to all other parts, we are now a Neo-Pangea planet. Probably the only animals to survive the Permian extinction were those living in rift valleys if the data about the oxygen levels thinning out disasterously except for these at or below sea level areas are true.
One major biodiversity hot spot today is the coast of Brazil.
The Atlantic Forest or Mata Atlântica stretches along Brazil's Atlantic coast, from the northern state of Rio Grande do Norte south to Rio Grande do Sul. It extends inland to eastern Paraguay and the province of Misiones in northeastern Argentina, and narrowly along the coast into Uruguay. Also included in this hotspot is the offshore archipelago of Fernando de Noronha and several other islands off the Brazilian coast.
Long isolated from other major rainforest blocks in South America, the Atlantic Forest has an extremely diverse and unique mix of vegetation and forest types. The two main ecoregions in the hotspot are the coastal Atlantic forest, the narrow strip of about 50-100 kilometers along the coast which covers about 20 percent of the region. The second main ecoregion, the interior Atlantic Forest, stretches across the foothills of the Serra do Mar into southern Brazil, Paraguay and Argentina. These forests extend as far as 500-600 kilometers inland and range as high as 2,000 meters above sea level. Altitude determines at least three vegetation types in the Atlantic Forest: the lowland forest of the coastal plain, montane forests, and the high-altitude grassland or campo rupestre.
The map above shows how South America and Africa nestled with each other 100 million years ago. Slowly, they began to grow apart and the fissure between them was very active. The center of South America and the center of Africa are depressions just like the center of the North American continent is identical. Indeed, it is rather amusing that these three continents which were, unlike Eurasia, pretty stable entities for the last 200 million years, all have these mysterious depressions.
In the news is this interesting tidbit about the Amazon.
EARTH SINKS THREE INCHES UNDER WEIGHT OF FLOODED AMAZON
As the Amazon River floods every year, a sizeable portion of South America sinks several inches because of the extra weight—and then rises again as the waters recede, a study has found.This annual rise and fall of earth’s crust is the largest ever detected, and it may one day help scientists tally the total amount of water on Earth.
“What would you do if you knew how much water was on the planet?” asked Douglas Alsdorf, assistant professor of geological sciences at Ohio State University. “That’s a really exciting question, because nobody knows for sure how much water there is.”
When I rotated South America back into its original position vis a vis Africa, one can see instantly how the Amazon drained into the gigantic rift valley between the two developing continents. Ditto the Congo river. Much of the water falling on both continents was channeled into that growing depression. One supposes it had many long lakes like the ones we see today in the Californian and East African rift valleys! Jungles and many lakes linking to each other in a huge conglamoration, with steep slopes rising on the South American side below the Amazon depression, this was the tremendous 'Garden of Eden' that spawned all the first mammals as well as the first flowering of the great dinosaurs.
When the Permian extinction occured, the accidental survivors were those creatures who lived in this very sheltered place. Even if desertfication and dessication raged across the planet, any water falling would flow into this vast rift zone. If the winds howled, they skipped over this rift zone. If there were tremendous tornadoes scouring the dead land masses, they hopped over this rift zone. Life clung to its barest essentials in this rift zone and when the plants and then the animals again emerged, it was from this generous cradle.
From 150 million years ago to when the continents finally split apart and the ocean rushed in about 100 million years ago, most mammalian as well as placental creatures had split off into today's family groups. Long before the annihilation of the dinosaur's reign 65 million years ago, most mammalian animals were already marching literally away from each other as the various continents spread apart.
Our insect eating, big eyed, tree climbing, nurturing only one or at most, two infants at a time, ancestors lived on both sides of the great rift split. This is why monkeys evolved on both continents. It didn't take long for Africa to bump into Eurasia and this accelerated the mammalian explosion which is still underway in the form of homo sapien biomass.
Hundreds of millions of humans now restlessly range about the planet every year.
Nearly 200 million people now live outside their country of origin - up by about a quarter since 1990, a United Nations report on migration says.
The report by the UN Secretary-General Kofi Annan says most migrants have gone to rich countries, and one in every five to the US.In some countries money sent home from abroad accounts for a large proportion of the national income.
Mr Annan said migration was a now a major feature of international life.
He described his report to the UN General Assembly as an "early road map for this new era of mobility".
When the second mass death hit, many mammals survived rather well, considering all things. Once again, as storms raged and roared after the meteorite strike, those sheltered by the mountains of the Brazilian side of the former rift valley could cling to the trees and endure it. And the animals living in various watersheds could move upslope to avoid the unusual floods created by the displacement of so much ocean waters.
Aside from these catastrophes, the environment of a rift zone is conductive to evolution since it cuts off populations from each other in many slight or large ways whereby they can develop sexual habits that emphisize differences yet are not so isolated like islands or mountains, where they never intermix with their foundation species again.
Robert Roy Britt
LiveScience Managing EditorElectric fish emit weak signals from an organ in their tails that serves as a battery. Different emissions signal aggression, fear or courtship.
While the fish can apparently understand each others' warning signals, "They seem to only choose to mate with other fish having the same signature waveform as their own," explains neurobiologist Matt Arnegard of Cornell University.
But in the Ivindo River in Gabon, Arnegard and colleagues have found fish with the same DNA emitting distinctly different signals. The fish are likely on the verge of splitting into two species, the researchers announced today.
"We think we are seeing evolution in action," Arnegard said.
Even when populations are not segregated from each other the frivolous choices made by creatures having sex propell evolution relentlessly forwards. In the chaos of the animal world when one wants to mate and have young, choosing carefully is of primary importance and various creatures evolve various obsessions and judgmental tricks to whittle down, who to have sex with.
Trees in the rift valleys evolved alongside insects and tree dwellers to get them to fertilize or plant the seeds so the forest could grow. Consumers of growing things have to be discriminating so they get maximum energy while using minimum labor and all these forces on top of avoiding being eaten by each other and strangers is part of the eternal, infernal machinery of evolution.
I live on a mountain facing a complex valley system. My home overlooks a very minor, extremely ancient rift zone where Africa collided with North America 400 million years ago. The geology here is very complex and extremely old. The great mountains which loomed over this rift zone have been whittled down to little nubbins today. Even so, it works as a classic rift zone even today!
The weather going up every 50 ft is different. Many a time, my son, going to school down in the valley below, would be warm up here and thanks to cold air falling when there is no wind, it would be freezing cold and wet in the valley even as the sun shines merrily here above.
Or the valley would be warm while freezing winds whip the forest around me only 100 ft above! When very violent storms come ripping across New York, the uplift of the Rensselaer plateau shelters our valley and tornadoes, hail, lighting and floods all skip overhead leaving us virtually untouched. The type of trees changes as one climbs the hillsides. The types of birds, when flowers bloom, when snow melts, what kinds of animals live where are all very strongly affected by elevation. The watershed caused by the rills of hills surrounding and feeding into the Taconic former rift zone make this a very rich biodivirse environment.
Listening to the frog populations in spring as the different species begin their courtship, first deep in the bottom bogs in the valley and then each week, a new chorus of diffent voices begin to sing until the amphibians living under the rocks and next to hidden springs high up the mountainside join last, it is an aural reminder of the power of rift valleys. The fireflies each have their own flashing system and they don't mate with each other, each zone avoids the zone above and below, some fly high, some stay low in the grass. The mountain tree dwelling fireflies coat the forest (alas! Not this year!) set the whole mountaintop afire in late June.
Moths and butterflies have their strict zones. The awful blackflies rarely pester me above my house but just below my house, they are extremely annoying.
Thanks to our valley/watershed/plateau uplift configuration, bird watching here is quite spectacular. We have a tremendous diversity of birds, on the ground and in the air. Several owl species, many song birds, water birds, raptors, scavanger birds, ground dwellers, every day, I see dozens of different birds here!
This makes me sensitive about saving the earth, saving diversity and understanding how all this amazing and wonderous generosity of life came to be.
Beautiful!!! You truly have an eye for colour.
Posted by: red bottom | October 13, 2011 at 03:17 PM