There was a forest in Greenland: DNA study reveals. What does it tell us about the climate

Every time an ancient code is deciphered, giving us snapshots of life in a time so remote as to be unusual and difficult to imagine for us, the public’s curiosity for the remote and the fantastic receives new satisfaction, because we learn details of remote eras that have the advantage of being true, rather than the fruit of the imagination of some scholar who ventures to hypothesize what there is no direct proof of.

The code of Hammurabifor example, has shown us what the laws were in 1750 BC, thus allowing us to understand much of how the society that produced it was organized and the concerns of the ancient inhabitants of Mesopotamia, as well as the Tabula Cortonensis illustrates the agricultural economy and property rights of certain Etruscan families of Cortona, or the most ancient Egyptian inscriptions testify of life in 3000 BC

From ancient codes, we reconstruct life, people, interests and landscapes; But what if we could decipher codes from millions of years ago—codes that contain information about life long before our own species appeared?

Today this question has a precise answer, because there is a particular code, written in “chemical characters”, which can provide us with answers on very ancient life, human and otherwise: it is the code written in the genome of every living being, in the form of a sequence of nucleotide bases. That sequence makes it possible to identify the presence of a particular living organism, e the abundance of traces of a given DNA allows us to estimate its abundance in a given place, in a certain era; this is because every living organism disseminates its own DNA in the environment, both for the simple fact that it dies, and also because it continuously loses cells, in the case of multicellular organisms. The examination of DNA in environmental samples, therefore, has long since become a powerful ally of ecologists, making it possible to estimate the species composition of a single ecosystem, as well as their relative abundance. The interesting thing, however, is that it has been realized that traces of this DNA, under particular conditions, can persist for millions of yearsfor example in frozen samples and absorbed to particular minerals that prevent their degradation.

Thus, a fascinating work has just been published in Nature, which gives us a snapshot of a particular environment from 2,000,000 years ago, or rather of the species that frequented it, with a detail and completeness that would not be possible otherwise. In the period between 3.6 and 0.8 million years ago, Earth experienced climatic periods similar to those predicted as a future consequence of ongoing warming. Many areas of our planet went through heavy crises, with desertification and sea level rise, while in the Arctic polar region they reconstructed themselves from detailed experimental data average annual temperatures of 11-19 °C above contemporary values.

A series of ice samples, dated to about 2 million years ago, taken in northern Greenland, in what is currently a polar desert, offer a snapshot corresponding to a lush forest. As environments became more inhospitable in many parts of the world, analysis of these ice samples yielded the oldest DNA fragments ever examined, allowing researchers to examine which species were found in an area that is now mostly uninhabited. The arctic landscape of this remote era has no modern equivalent: it is neither boreal nor temperate forest. Birches, cedars, horsetails, herbaceous plants and many other plant species, totaling over 100, constituted a unique community, which took advantage of the long arctic summer photoperiod and temperate climate. Various species of insects fed on these, including ancient ants, whose DNA has come down to us; but vertebrates also abounded, with nine species never before identified in Greenland, including mastodons – that is, American mammoths – rodents, rabbits and ducks from the same group as our Canada geese. Even the DNA of the fleas that afflicted these animals has come down to us; and then, surprisingly, the DNA of marine animals that lived on the coasts of that ancient forest, including horseshoe crabs, various components of plankton and microalgae, all of which are now widespread only much further south.

However, the result of the work goes beyond the story of Greenlandic life millions of years ago: it opens up the possibility of sampling the past of life on our planet in different times and placesreconstructing the flows of species and ecosystems that have characterized the sequence of environments and climates over millions of years.

Species that flourished with the favorable climatic variations, to then disappear more or less definitively in conditions adverse to their biology, giving way to others; the story that the code of the ancient DNA can tell us is not only the story of a wonderful Eden, but should contain a teaching that concerns us closely and that anyone who is not cognitively blind should be able to grasp.