The Earth emerged from the endless cycle of glaciations and warming, and humanity was able to create civilization thanks to the strengthening of currents and the "escape" of a huge mass of CO2 from the waters of the southern oceans of the Earth. Paleoclimatologists write about this in the journal Nature Geoscience.
“We seem to have found the answer to this interesting historical riddle. The strengthening of currents in the southern oceans of the Earth allowed the carbon dioxide contained in their waters to “escape” into the atmosphere and warm up the planet. A very small amount of CO2 got there, but it was enough to stop the cold snap and the birth of civilization,”said Daniel Sigman from Princeton University (USA).
The last ice age in the history of the Earth, as geologists today believe, began about 2.6 million years ago. Its main feature is that the area of glaciation and the temperature of the Earth's surface throughout its entire length were not constant.
Glaciers were advancing and receding every 40 and 100 thousand years, and these episodes were accompanied by sharp cooling and warming. The last period of warming began about 13 thousand years ago and continues to this day.
These cycles of glaciations and "thaws", as many scientists today believe, are primarily associated with the so-called Milankovitch cycles - the "rocking" of the Earth's orbit, changing how much heat is received by the poles and temperate latitudes. Other geologists and climatologists believe that, in fact, these abrupt climate changes are associated not with "space", but completely terrestrial factors, such as restructuring of the "conveyor" of currents in the oceans or an increase or decrease in the proportion of CO2 in the atmosphere.
Scientists have long debated whether the Earth has emerged from this cycle of glaciations and warming, or whether the current "thaw" is part of these long-term fluctuations. For example, the supporters of the first group of theories suggest that the planet's climate changed irreversibly 20-15 thousand years ago as a result of volcanic eruptions or some other catastrophic events that emitted large amounts of CO2 into the atmosphere.
Sigman and his colleagues uncovered the cause of these changes by studying rock samples excavated from the bottom of the southern corners of the Indian, Pacific and Atlantic oceans. In addition to rocks, climatologists analyzed changes in the growth rate of coral reefs that have existed on their territory for several thousand years.
Analyzing the proportion of nitrogen isotopes in these sediments, scientists tried to estimate how much organic matter and carbon dioxide ended up on the bottom and in the deep waters of the ocean, and how much of them returned to the surface. As a rule, the lower the proportion of "heavy" nitrogen-15, the more organic matter and CO2 had to "escape" from the depths of the ocean and enter the Earth's atmosphere in one way or another.
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It turned out that the proportion of nitrogen-15 was gradually decreasing throughout the Holocene, the last geological era that began about 13-14 thousand years ago. During this time, the concentration of heavy nitrogen dropped by 0.2%, which is equivalent to an increase in CO2 in the atmosphere by 20 ppm, or about 7% of its concentration in the pre-industrial era.
What could have accelerated the "escape" of organic matter and CO2 from the deep layers of the ocean? As scientists suggest, this phenomenon was associated with the strengthening of westerly winds and the acceleration of currents in the temperate and polar waters of the Indian, Pacific and Atlantic oceans.
Due to this, temperatures on Earth have remained stably high over the past 13 thousand years, and did not gradually fall, as it happened in the past interglacial periods. This allowed humanity to move to a sedentary lifestyle and create a civilization, the authors of the article conclude.