Throughout its checkered history, along with falling meteorites and the very likely collision with a smaller planet whose remains formed its only major satellite, the Moon, our planet has gone through at least five glacial periods or ice ages, the first about 2,000 million years ago, and the most recent, called Quaternary, which began about three million years ago and continues to this day. In the periods between ice ages, there was no eternal ice on our planet even in the most extreme latitudes, but today we have polar caps and other glaciers that reveal what era we live in.
Ice ages or glaciations experience warmer and colder phases in their course. In the cold ones, large masses of ice extend from the poles, the level of the oceans that provide that water drops significantly and snow falls at lower levels.
So for about 11,000 years we have been in an interglacial phase of the Quaternary ice age, in which our species has prospered after overcoming years of intense cold whether they lived in the north or migrated to it.
Periodic ice ages
The ice ages our planet has experienced, and the phases within them, are periodic and are governed primarily by the amount of sun the Northern Hemisphere receives in summer. Why the northern hemisphere? The fundamental explanation is that this hemisphere today has more land mass than the south, so that the ice can advance more in winter and melt less in summer, while in the south there is not enough land mass for the slight variations in irradiation of the sun have the same effect, although certainly its ice also advances.
The amount of sunshine the Northern Hemisphere receives increases or decreases due to three factors related to the Earth’s movement around the sun. First, the orbit of our planet is, like those of all other members of the solar system, elliptical, but sometimes the ellipse it travels is slightly more elongated due to the gravitational attraction of the two largest planets: Jupiter and Saturn, simplifying enormously. When it is more elongated, something that happens every 413,000 years, the northern hemisphere receives less sun.
Second, the inclination of the Earth’s axis of rotation with respect to the plane of its orbit varies between 22.1º and 24.5º in a cycle that lasts around 41,000 years.
Thirdly, the axis of rotation of our planet changes its orientation or direction slowly and continuously, caused by gravity.
Together, these and other less relevant changes in the Earth’s motion are known as Milankovitch cycles by the Serbian geophysicist who first speculated on its meaning in relation to the ice ages: Milutin Milanković.
When these cycles come together and the northern hemisphere receives less sun, ice ages and also the phases within them occur.
There are scientists who suggest that human action has altered, even radically, the cycle of glacial and interglacial phases, which could equally accelerate the next one or prevent it from occurring.
This, by the way, does not mean that climate change will be ‘balanced’ with the arrival of a new glacial phase in a future that may be hundreds or thousands of years. In fact, there are scientists who suggest that human action has altered, even radically, the cycle of glacial and interglacial phases, which could equally accelerate the next one or prevent it from occurring… so we face an uncertain future that we must deal with. to manage as a species.
Discover and study them
For much of history, even when the explanation of the strata on the surface of our planet was not known, a peculiar accumulation of sand, gravel, mud and sediments without order or order had been observed in certain areas of northern Europe and America. concert, some of them clearly not belonging to the type of minerals in the area.
As the biblical explanation had not yet been seriously discarded by science, it was common to assume that these were remains transported by the Universal Flood and left there when the waters receded. A variation suggested that this debris had arrived on glaciers floating in the waters that covered the land.
It was not until the 19th century when the hunter Jean-Pierre Perraudin he showed the engineer Ignace Venetz that the marks on the glaciers in the valleys of the Alps had been produced by other larger glaciers. Venetz conveyed the idea to the geologist Jean de Carpenter, who confirmed that some rocks had been moved by glaciers that had been there after the Alps mountain range formed. For his part, the botanist Karl Friedrich Schimper had reached the same conclusions. The idea was not well received except by a friend of both, Louis Agassizone of the most respected scientists of the time, who found it solid and proceeded to study and confirm it… and who in the end would take credit for the discovery of the ancient ice ages, much to the chagrin of his friends.
Starting with Agassiz, geologists, climatologists and other specialists developed the science of paleoclimatology, the study of the climatological past of our planet, reconstructing it from the study of rocks, sediments, perforations in the ice and in the earth, ice sheets. , tree rings, corals, mollusk shells and large and small fossils.
23,000-year-old mammoth tusks found under the ice in Siberia.
FRANCIS LATREILLE / AP
The study of this climatological past and the ice ages that marked it allow science to advance our knowledge of the development of life and the appearance of our world. The extinctions of species related to the ice ages, such as the large animals that disappeared at the end of the glacial phase 11,000 years ago (mammoths and woolly rhinos, the wild horse in America) as well as the survival strategies of others such as reindeer, musk oxen or bison, which migrated and adapted to the new reality, allow us to better understand the flexibility of life and the future prospects of our planet.
But also the adaptation of human beings to the ice age, language, clothing (which requires the invention of sewing, needle and thread), hunting weapons and tools to take advantage of collected prey tell us the story. of some of those extinctions that scientists already attribute to the presence of those primates that would eventually become you and me.
Pierce the ice
One of the techniques of paleoclimatology is drilling, especially in ice, to obtain long cores inside which scientists can analyze the content of substances such as carbon dioxide in the waters of the past, which tells them what the environment was like. , the climate and even life, with the microfossils, pollens and other remains that have been locked in the ice for millennia.
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