When we look back at the first humans as they spread across the globe, we are usually constrained by the coastal areas marked on maps. But people didn't only move through the heart of continents, they also trekked along their margins, by the coast, using the resources provided by the sea.
During the Ice Ages, vast quantities of water was trapped in the thick ice shields that covered the polar parts of the world, from 1.5 to 3 km (1-2 mi.) thick, the ice held so much water that the sea levels dropped, exposing areas now submerged along the continental shelves around the globe.
These areas were dry land for thousands of years. The exposed seabed thrived with plants and animal life. Trees, grasslands, rivers that flowed across them offered an environment suitable for our ancestors to live.
Some of the best known exposed continental shelves are: Beringia (spanning Bering's Strait between northeastern Siberia and alaska), Sahul (encompassing Australia, Tasmania, and New Guinea, Sundaland which included insular South East Asia: Borneo, Java, Sumatra, Flores, Bali, and the Malay Peninsula), and Doggerland (now submerged by the North Sea between Britain, Denmark, Belgium, Germany, and the Netherlands).
But there were many more spots that were used by humans, and also by our ancestors, the Denisovans and Neanderthals, to migrate, hunt, and live.
The forgotten Submerged World of our Ancestors
During the peak of each Ice Age, sea levels dropped up to 120 meters (400 ft.) and this exposed up to "15–20 million km2 of land" (5.8 to 7.7 million square miles) this is equivalent to 50-66% of the surface of Africa, two to three times the surface of Australia, or two to three times the area of the lower 48 states of the U.S. (21 to 28 times the area of Texas).
The map above shows a large area along the north coast of Siberia, Europe and Canda, but this was under the ice sheets, and the map with its Mercator projection tends to inflate the size of polar areas and diminsh those of mid and equatiorial latitudes. As you can see, Australia, Sunda, Japan-Taiwan-Korea, Southern South America, the mouth of the Amazon River, the persian Gulf, the Aegean Sea, the Gulf of Mexico, and the Atlantic Seabord of USA have the largest emerged areas.
The area of the continents is around 148 million km2, so the ice ages exposed an additional 10 to 13.5% of dry land, now submerged beneath the waves. A territory that is unexplored.
Archaeology under the sea is almost non-existent, and except for the rare artifact brought up by chance during fishing (like the Denisovan jawbone Penghu-1 from Taiwan) or the Homo erectus bones dredged by Berghuis, 2025 in Java) we know little of what exists on the continental shelves.
A paper by Norman et al., 2024 described the now submerged shelf along the northwestern coast of Australia, modelling its environment and population. The authors mention the importance of subaquatic archaeology, and also noted that the flooding after the end of the last ice age was very fast, sea levels grew by 1 meter (3 ft. 4 in.) per century and accelerated to 4-5 m (13-16 ft) per hundred years for over 400 years around 14.1 kya. This was followed by a second flood, that lasted 3000 years, beginning 12 kya, which was also fast. The flooding pushed the people living on the sea shores into the interior of the continent, a period of stress and adaptation to new enviornments and resources which is reflected in the rock art styles that changed and seem to depict "conflict/battle scenes."
Americas
The submerged coastal areas of North America along the shores of Canada, Alaska, Washington, Oregon, and California surely contain sites with artifacts and campgrounds of the first people to reach America. Although narrow, this shelf holds evidence about the earliest humans in America. On the Atlantic coast, the continental shelf is far wider. In a recent post I mentioned the 22,000-year-old Cinmar site off the coast of Virginia, in the Atlantic Ocean, 47 mi (75 km) from Chesapeake Bay.
The Pacific coastline, is steeper in Central and South America, as the Andes run very close to it, and the seabed plunges into the ocean depths fairly quickly. But on the Atlantic coastline of Argentina, Uruguay and southern Brazil, there was a vast flat area that stretched for hundreds of kilometers eastwards from the current sea shore. Below is a map that depicts the current, and the now submerged terrain of South America (the white dots are sites where pollen was collected for an analysis of the plant coverage).
The paper in which the map shown above, was published, by Díaz Pinaya et al., 2024, describes the "Southern Atlantic Continental Shelf Connectivity (SACS)" had trees of many species, like "Araucaria and Drimys, forming plant assemblages with Arecaceae, Ericaceae, Ilex, Myrsine, Myrtaceae, Podocarpus, Symplocos and Weinmannia. It includes Atlantic Rainforest sites extending from the Mantiqueira Mountains, the modern cerrado region of Minas Gerais into the Serra do Mar highlands along the coast of southeastern and southern Brazil. Considering the LGM landscape, this floristic connectivity extended from the Central South American Connection (CSAM) onto the then-exposed Atlantic Shelf spanning from 23 to 56°S in latitude. We hypothesize that this large exposed area was vegetated by cold and humid successional forests as a consequence of the downward migration of montane taxa into the coastal lowlands, a scenario supported by pollen records." During this period, the araucaria of the Paraná region (not the Patagonian variety of monkey-puzzle) is believed to have expanded "into Uruguay and northern Argentina, especially onto the exposed continental shelf. Drimys, on the other hand, appears to display high niche suitability centered in southern/southeastern Brazil, on the Argentinian shelf and in a large area between 36 and 48°S on the Pacific coast of Chile. Drimys winteri... an Andean endemic, could have populated the latter two regions"
This paper estimates the emerged continental shelf along the coasts of South America at 1.94 million km2, which is "equivalent in size to the combined areas of France, Spain, Germany, Italy and the United Kingdom and that in southeastern/southern Brazil/Uruguay and Argentina the past coastline was 200–250 km and 500 km distant from its present location, respectively."
The Araucaria and Drimys (in the Patagonian forests, the latter survives as the Winter Bark, or Canelo, Drimy winteri) would have expanded along the southern part of the shelf, colder and wetter. In the other parts, further north it would have been similar to the present day Atlantic Rainforest with different levels of trees, possibly five tree layers with different tree-heights, from 50 meters (150 ft) to tree ferns and shrubs at the lowest level. The authors point out that "the South American Continental Shelf, which could have created an important migration corridor for different southern Andean plant species to migrate northwards and colonize areas of the Brazilian Atlantic coast. Our data suggests that this vast coastal corridor was possibly covered by temperate-like forest with prevalent Andean floristic affinities in the south and a more Atlantic floristic composition in the north."
This scenario of forests and jungles is very different from the grasslands and prairies of Uruguay, and the Pampas region of Buenos Aires in Argentina, and the arid steppes of Patagonia. The people living in South America during this period (if we accept them having reached the region 25-30 kya) would have enjoyed a rich environment that is now totally submerged. I
The difficulties and limitations of underwater archaeology
Unfortunately, most of this submerged area is part of Argentina's continental shelf. Research funds are limited and scarce in Argentina, so very few underwater sites have been studied (see Ciarlo, 2009). Most of the underwater sites involve post-European-Discovery sites like ships or inland places in lakes. In Uruguay, where the situation is similar, there have been "increasing discoveries of archaeological material from submerged sites redeposited on beaches by storm events" (see López Mazz, 2004) these findings include fossils of megafaunal animals from the former deltaic area of the River Plate, now submerged by the sea.
Underwater archaeology is complex, expensive, and requires scuba diving gear and special equipment such as pumps, support shipes, etc. Easton, Moore, and Mason, 2020 (free access) describe the experience along the coastal area of British Columbia in Canada, showing that although it is feasible, it will not become mainstream in the forseeable future.
Underwater sites often lack stratigraphic context, and objects dredged up from the seabed are isolated from their original emplacement making it hard to reach useful conclusions about them. For instance the "Chinese anchors" dredged off the ocean floor close to Catalina Island, California in November 1973 have been controversial. Brought up from the bottom by a United States Geological Survey expedition from the Patton Escarpment, the donught-shaped stone was believed to be part of Chinese Junk dated to 3,000 years old. It was followed by the discovery of stones shaped like Chinese anchors at Palos Verdes Peninsula, close to Los Angeles by Baldwiyn and Meistrell in 1975 (see these two references: Mc Ginty, 1983 p. 54, and University of San Diego, 1980 p. 4). However, Frank Frost, 1982, suggested they were recent, not more than 100-years-old.
Comments
With the main migration corridors, and sites linked to the shores of lower sea levels, now submerged and out of reach, how can be so sure about the dates for the movement of people around the world?
It is reasonable to assume that the first migrants exploited the coastal environments before spreading inland into the continents, yet we can only access sites located on dry land, which are certainly younger than those under the sea.
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