Foraminifera.
To investigate the hypothesis of the existence of an "advanced" society (whether or not called Atlantis) in times or places today unexpected, it is convenient to summarize the framework of knowledge in our possession today. Let us start from the Ice Ages.
Natural oxygen is almost exclusively composed of two isotopes: O16 and O18. Water containing O16 is lighter, evaporates more easily, and thus is present in greater proportion in the clouds, from which it falls as rain or snow. When large amounts of snow end up in ice sheets, the content of O16 in the oceans decreases. Since some marine organisms, such as foraminifera, fix sea water oxygen to form the calcium carbonate of their skeleton, their shells record the O18 / O16 ratio at the time of their lives.
In practice the remains of foraminifera, layered on the bottom of the oceans can give us indications on the size of glaciers up to five million years ago (Lambeck et al., 2002) [1]. From these layers it results that, after two million years basically calm, around three million years ago the temperature of the earth surface began to swing between glacial periods (commonly called Ice Ages ) and interglacial ones, giving rise to what we call the Pleistocene epoch.
Figure 2) shows a carrot of ice 800,000 years old, photographed at Dome C in Antarctica. The climatic conditions of Antarctica ensure that snow does not melt, but set down in layers, one above the other. Since seasonal variations characterize each annual layer, it is possible to distinguish one year from another, as the annual tree rings. In some places of Antarctica these deposits of pressed snow are almost 4 km deep. Given that the average annual thickness is about 4 mm, it follows that the snow at the base fell almost a million years ago.
Consistently, the succession of Ice Ages indicated by foraminifera has been confirmed, for the last 800,000 years, by the measures of O18 trapped in Antarctic ice (Epica, 2004) [2] and, for the last 120,000 in Arctic ice (North Greenland, 2004) [3]. Obviously, the details increase as we get closer to present, so the temperature trend during the penultimate interglacial period (120,000 years ago), the last Ice Age (from 110,000 to 10,000 years ago), and the present interglacial (which began about 10,000 years ago) is known with great precision. Moreover, there is a general agreement between the Arctic and the Antarctic data, confirming that almost all major climatic events have been global (Epica, 2006) [4].
The difference in temperature between glacial and interglacial periods (which could be up to 10 degrees °C) was not the only diversity. The water accumulated in continental glaciers was obviously lacking in the oceans, which were emptier. The sea level depended on the temperature and the cold peak was 120 meters lower than today. Consequently, the coastline was another one, several shallow seafloors were then emerged and men, who always tended to live near the sea, lived there. In general human territorial occupation followed the movement of the coastline, causing cascade effects on populations living further inland. In other words, it is since the penultimate interglacial (110,000 years ago), that the climatic change has been cause of migrations, conflicts and redistribution among human populations.
[1] K. Lambeck, T. M. Esat & E. K. Potter, Links between climate and sea levels for the past three million years. Nature, 419, 14 sept 2002, 199.
[2] EPICA community members (2004) Eight glacial cycles from an Antarctic ice core. Nature 429, 623-628.
[3] North Greenland Ice Core Project members (2004) High-resolution record of Northern Hemisphere climate extending into the last interglacial period, Nature 431, 147-151.
[4] EPICA community members (2006) One-to-one coupling of glacial climate variability in Greenland and Antarctica. Nature 444, 195-198.
[5] Siddall M, Rohling EJ, Almogi-Labin A, Hemleben C, Meischner D, Schmeizer I & Smeed DA. 2003. Sea-level fluctuations during the last glacial cycle. Nature 423, 853-858.
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