Science seems to be in general agreement as to how the lands were variously attached at the time that they were last all one land. Many even propose that one of the rivers which 'crossed' the land at that time is for much of its course approximately where the Amazon River is today, runing across the land identifiable as being that which we know as South America today. Of course at that very 'early' time, they consider the river ran from the east to the west, emptying at the western edge of the land into the Oceanic waters west rather than to the east, into the Pacific rather than into the Atlantic as we know it today. This one land they have entitled Gondwanaland. One of the most identifiable connecting points of this one land is that between the lands we identify today as the West Coastal regions of Africa and the Northern and Eastern Coastal regions of South America. Of course being such a dynamically removed period ago the exact shapes then have been 'estimately presumed', even by science, to be the same shapes of some of the 'continental lands of today, which in truth cannot truely be atested to.
The unusual asspect of a scientifically proposed river in Gondwanaland which parallels the Amazon today but with opposite river flow direction bears a closer look. The western outlet of the more 'ancient river' would seem to be approximately located in the regions of what is Lake Titicaca today in southern Peru and northern Bolivia and there is an the actual existence of a 'natural spilway' preserved in that rigion that though dry today marks a time when such a waterway did empty into the Pacific. Now presuming that this at one time marked the extent to which southern Peru once reached before being cut off by a major a 'waterway' or water division from the land of Bolivia, one can image a much more compact north to south reach of that land than all the way to the southern tip of Chili. And this presents an interesting perspective to consider in defining the early B.C. dated lands of the Book of Mormon from the 'Narrow Neck' of land to what was termed to be the Sea South, implying the land may have merely ran from Colombia through Ecuador and Peru. This will be explored further.
Exactly how the 'lands' looked with their precise coastal appearances is not known but merely presumed to be as they are today. Most graphic presentations merely present the one land connected with what is lined out in terms of what we today would recognize as the continental shapes we are familiar with. There must be some question as to whether such continents as South America would have really maintained its current 'today's' recognizable western coastal shape and image or not. In reallity, most likely not, as much of its western coast is composed of the great land uplifting events and presures with what is termed the Pacific or actually Nazca and Antartic plates and the continously forming Andes which even continues today but at a much reduced rate of uplift in terms of plate tectonics theories.
Thus presumably, to easily identify such for their audience, science usually depicts the division of the lands in the currently recognizable continental shapes without much coastal distortion compared to today's coastlines despite their claimed hundreds of thousands of years over which their division of the land is theorized to have occured. To completely presume that such coastlines were then and now over hundreds of thousands of years would be and is an over simplification jump of assumption which is not supportable. And it would seem that their most favored depection is just how the 'mega' land plates of the continents of today's South America and Africa did divide apart, pushed by the volcanic ridge or rift of today's mid-Atlantic Ocean until South America ended up alone in the southern portion of today's Western Hemisphere. And even that is a 'great jump' of supposition that South America has allways been one single recognizable piece of continuous continental land mass.
What 'mega' land plates did or did not brake off between what is South America and Africa today and their exact coastal shapes and evolution over the time of the land's division is not ascertainable but only can be theorized. Science does show that various parts of various lands today were once at the ocean's floor and visa versa. Thus most all Gondwanaland separation models are very generalizes theorized guestimations at best. Though for such general understanding of the concepts involved they are quite usable to conceptualize how the land was once one and did divide.
Conceptually, the land plate(s) of South America were once rather level and in one piece of land, meaning they had not yet been broken up into great mountain peaks of heights exposing the 'seams' of the earths crust so often displayed in mountianous regions. [This may sound familar as there is a similar description given in the Book of Morman in Samuel the Lamanite's prophecy and according to its fullfilment (Helaman 14:21-22 & 3 Nephi 8:18) relative to the great earth forming events caused by the destruction that happen in the land at the time of the death of Jesus Christ, as the land was once solid and seen in broken up pieces and in seams everafter the desctruction.] The 'cause' of such geographic land uplifts is caused by the presures of 'coliding' land plates such as along the western coast of South America where one such plate is lifted and broken upward as the other is 'crushed' and sinks below the other. Such 'collisions' are today for the most part 'gradual' occuring events and great earthquakes can even mark their occurances today but in less frequency than such a rapidly occuring uplift would manifest. This uplift which seems to have caused the great nearly continuous rocky mountain range from Alaska to the southern tip of South America is locally depicted in the western uplift motion graphically shown here which raised the great Andean Mountion range of South America.
As just mentioned, according to the Book of Mormon, one such time when the face of the land, north and south, was changed exposing the 'seams' or layers of the crust of the earth where once they were not so readily visible was during the great catastrophic destruction which occured in the land of promise at the time of the death of Jesus Christ. And what is not usually shown in the 'uplift' motion causing the Andean range is the fact that the eastern land plate(s) of South America had been moving west from the east causing their own contributing forces to the more complete picture of the plate motions and uplifts going on. The continuous dividing apart between the African land plate and the South American land plate(s) was and still is the ever driving force of the Mid-Atlatic Ridge [at only 2cm/yr today] with its own continuous seam of ocean floor volcanic force which seems to run nearly continuously from north to south the full length of the height of the Atlantic Ocean between the Eastern and Western Hemispheres. The Book of Mormon even makes a specific mention of a 'great mountain' being created during the there recorded destrution (3 Nephi 8:10). I have come to personally consider that the Sierra Nevada de Santa Marta range and its highest peak of the nation of Colombia named 'Cristobal Colon' is to be looked to as this 'great mountain'. [Cristobal means 'bearing Christ' or Chistopher]
Then again, there is another matter which science does set forth concerning the forming of what is today South America as we know it. And that is over some tens and even hundreds of thousands of years ago as South America was forming, the once theorized western flowing river of Gondwanaland previously alluded to, did swell up when its western outlet was first closed off and then filled up and expanded and formed into a great Amazon Sea which paractically filled the entire of the interior of the South American Continent according to scientists before it dissipated via the now reversed eastern flowing Amazon River which drains the Amazon Basin today. These supposes that the Andean uplift did seal the western outlet until the most ancient river left over from Gondwanaland did backed up into a great inland sea until the western uplift surpassed the eastern elevations and forced the great formed 'Amazon Sea' backwards and out its present east coast outlet of today. On a Bible and Book of Mormon time scale, the enitial 'Andean Uplift) likely first began some years after Peleg and if the 'inland Sea' was already present betwix the 'west coast' of today's South America then the vaulting of the land may have mostly occured at the time of Christ's death and that would have been when the 'sea south' of the Book of Mormon would have changed and the Amazon basin uplifted upon the west to begin to fill in from the Adean silt, closed off western access and the drainage of the 'inland sea' out its eastern outlet. Interestingly enough there is still what may be considered a northern outlet if one considers the 'natural canal' which connects the Rio Negro branch of the Amazon river to the Orinoco river. By that route still open today, you can boat up one river and out the other from the Atlantic to the Carribean or visa versa.
Of course these from a pure scientific perspective are generalized theories spanning thousands upon thousands of years. They span such a lengthy duration of time and are based upon a few observations and conclusions based upon a small amoumt of detail. One such fact is that in Argentina up along the plains and course of the Panaro River there have been found the 'bone' 'not fosil remains' of such things as the teeth and jaws of sharks for a great distance inland. And there is the courious fact that the Orinoco River and the Amazon River even today continue to form a dividing waterway which separates the land and which allows the sailing up the one and via such 'connecting' rivers as the Rio Negro and a natural formed canal and down the other. It is the only place in the world where two such rivers connect in their 'headwaters' forming a continuous water course from Ocean to Ocean, or in this case the Atlantic Ocean to the Carribean Sea without being considered by most as a division of the continuous South American Continent. Who and what, besides the brown color silt filled river from the Andean mountains which gives the Amazon its color as it empties into the Atlantic did determine that that was the course of the river's mainstream named the Amazon, and not the continuous course of the River on up the Rio Negro and by the natural canal back to the Ocean via the Orinoco as the true course of the 'River Sea' of the Amazon, is not known. Certainly a river's course that never ends must legitamately be considered as a part of that same river. Without the brown silt of the Andes coloring the water, who is to say that particular 'stem' of the river is a tributary and not the main course of the river which runs on around to the north and back out to sea, forming a continuous loop of navigitable waterway surrounding the whole of the northeast corner of what is supposed to be a continent.
Whether the once Great Amazon Sea was a land locked sea with only a single outlet such as the Medeterranean Sea, Caspean Sea, and Black Sea; or whether it was an extention of the Ocean compassed about by various large Islands is a quandry to consider. The Phoenecians are on record as recording two large Islands some distance off the coast of Africa. One of which they called 'Iron Island'. That these two eastern Islands mark the land masses and coastal regions of Eastern South America today is of some question. Certainly the 'Northeast Sector' framed off by the continuous waterway about the land would be one such candidate for consideration as one of the islands off the coast of Africa about 1000 B.C., mid duration since the time of Peleg when the Bible sets forth that the land was first divided from Africa some added 1,000 years prior according to the Bible account. Then when the major land island's colisions caused such tremendous destructions as recorded in the Book of Mormon about 34 A.D. would mark the ending or the beginning of the ending of the Amazon Sea and it being turned into but the world's most volumous water course on earth.
All in all, there would seem to be at least three Islands surrounding the ancient Amazon Sea which according to Scripture would have existed and been refered to in the Book of Mormon as the Sea East. There would be (1) Jacob's Island as recorded in the Book of Mormon and the two Islands (2) & (3) of the Phoenecians with the Amazon Sea in the midest of them as depicted with a long string of mountainous regions spaning down along what is Chili today. Jacob's Island would be bordered upon the south by the ancient outlet 'casway' about the Titicaca region of the old 'Gondwanaland' unity from the time of the days of Peleg according to the scriptures. Its east coast would be bounded by the Great Amazon Sea which Scientists agree existed during the period of the duration of the dividing of the land until South America takes on its unified shape it is in today. Reconciling the Scientific time table to the Scriptural time table of the division of the land, would establish the Amazon sea to be in existence when the Book of Mormon referenced a Sea East. Of course the Pacific Ocean would be the Jacob's Island's Sea West and depending of Lehi's group's ability to have found the narrow passage north prior to traveling south from their landing sight just south of the Isthmus of Darien or whether that narrow neck was inundated by the La Nino year which brought Lehi's party to land at such a location as what could be considered for Jacob to have come to a conclusion that indeed they where upon an Island of the sea surrounded by water and in fact most nearly surrounded by water except for the narrow neck and passage to the land north.