A world is disappearing

New studies illustrate the dangers of the extinction of large bees

The extinction of the dinosaurs about 65 million years ago changed the history of life on Earth. Most scientists today accept the explanation that the extinction was caused by a large asteroid impact, which caused huge dust clouds to be blown up all over the world. In addition to this, the emission of hot material from the shell of the DHA caused the heating of the air, the evaporation of water sources, fires and the formation of a lot of soot in the air, in addition to the dust. All of these severely damaged the vegetation, as a result, plant-eating animals became extinct, and in their wake came the carnivores, which feed on the plant-eaters. Thus, along with the dinosaurs, many other species of plants and animals became extinct, including the ammonites (ancient marine snails whose shell size sometimes reached several meters), many algae, and various species of microorganisms. This extinction paved the way for the development of a group of animals that until then had a marginal place on Earth - the mammals.

Change of government

In the age of dinosaurs, most mammals were tiny rodents - mouse-like, but in many cases even smaller than them - that were active mainly at night and fed on insects or dinosaur eggs. However, the disappearance of the masters of the land allowed mammals to develop relatively quickly into new species, and to take over many habitats. Within a few tens of millions of years, many species of mammals - including giants - are the masters of the new land and sea. However, in the blink of an evolutionary eye - less than two million years ago - a new, medium-sized mammal appeared, which changed the face of our world beyond recognition. The new mammal spread from Africa to Asia and Europe, eventually reaching all parts of the planet. A series of studies published this week in the Proceedings of the American Academy of Sciences (PNAS) illustrate how destructive the spread of the new mammal - it is man, of course - was to other species and to nature as a whole.

A very cold bridge

In 2006, a team of engineers and workers were engaged in measurements for the laying of a railroad in central Alaska, when their men discovered a hunters' camp from about 11,500 years ago. Extensive archaeological excavations were opened at the site, and in 2013 one of the most intriguing findings from the period was discovered there: the skeletons of two babies. One of a 6-12 week old baby, and the other of a fetus born prematurely, probably in the 30th week of pregnancy. The hunters in the camp probably buried the babies in the ground, which allowed the bones to be preserved. As of today, these are the oldest remains of humans in the Americas, or more precisely - the oldest remains from which DNA samples could be extracted (other bones that were discovered were from humans whose bodies were burned and their genetic material was destroyed). The researchers analyzed the mitochondrial DNA of the two babies - this is DNA that is not found in the cell nucleus but in the mitochondria, and its uniqueness is that it is passed from generation to generation only through the mother. In this way it does not mix with that of the father, allowing long genetic lineages to be traced. In the new study The researchers compare the DNA of the babies (who come from different mothers) to that of different populations in the Americas, and conclude that this is the most ancient link in two genetic lineages that currently exist in different regions in both North and South America. According to the researchers, from the University of Utah, the findings greatly strengthen the hypothesis that most of the populations in America are descended from tribes that came from Northeast Asia through the Bering Straits - which today separate Russia and Alaska. Scientists estimate that due to the lowering of the sea level, there was a land bridge in the straits for about 10,000 years, until about 18,000 years ago when the ice age ended, the glaciers melted and the sea water rose again and separated the continents.

The camels of America

Not only humans came to America across the land bridge from Asia. About 15,000 years ago, America had many large mammals: mammoths, mastodons (ancient elephants), and large populations of camels and wild horses. These mammals were there long before humans, and may have themselves reached the Americas on very early land bridges. It is almost indisputable that from the moment man set foot in America, the large mammals there became extinct at a dizzying speed. Already more than 40 years ago, an American researcher hypothesized that the path of extinction of these mammals coincides with the path of human expansion. Now researchers from the University of Wyoming suggest New evidence for the correctness of the hypothesis. The researchers used radiocarbon dating to determine the age of the large mammal fossils. Carbon, which is a central component of all organic substances that are the basis of the animal and plant world, appears in nature in several forms - isotopes. The most common carbon is called carbon 12 - about 99% of the carbon atoms in nature are of this form. About one percent is carbon 13. Only one out of every trillion carbon atoms is an atom of carbon 14 - unlike the other two isotopes, it is a radioactive substance that decays gradually. It takes about 5,700 years for half of the amount of carbon-14 to decay into other elements, and it is this timetable that makes this dating method so effective. We check how much carbon 14 is in a sample of a certain biological material, and based on the missing amount we can guess how long ago it was formed. An age test of extinct mammal bones revealed that in Alaska the main extinction was from 15,000 years ago to about 13,300 years ago. After that - 13,200-12,900 - years ago, most of the large mammals disappeared in the area that is now the continental USA, and during this period and the continuation, until approximately 12,600 years ago, the mammals in South America also disappeared. These findings are consistent with the hypothesis that hunting by humans was the primary cause of extinction of mammals in the Americas, and that humans did reach the Americas through the same Bering Strait land bridge.

burning matters

The widespread extinction of large mammals by humans was not a phenomenon unique to the Americas. Researchers estimate that wherever man spread to, there was a widespread extinction of large mammals, mainly due to hunting. However, this extinction had a real environmental cost, in addition to the disappearance of the animals that were a source of food, skins, fat, and tools made of bone. Large mammals engineer their environment significantly, And a new study states Because their extinction caused an increase in the number of large fires, even nowadays. An international team of researchers, led by scientists from the Netherlands, determined that the large mammals create trails in the vegetation, reducing the possibility of the spread of flammability. They also show in the research that in areas where there are still relatively large mammals - such as moose for example - in large quantities, there is less danger of large fires.

Dry the food source

A fire is indeed a very dangerous event for humans and animals, but it is a local and natural event, and even an important process in the regeneration of natural vegetation. In contrast, large mammals and other animals have other major roles in maintaining the environment, and as far as they are concerned, the damage caused by the extinction of the animals is apparently irreversible. One of the main effects of the large animals is the recycling of various substances in nature, primarily phosphorus. This element is one of the most important for the existence of life, because it participates in many processes in the living cell. Phosphorus is also one of the substances that plants absorb directly from the soil, so it is a key component in natural and artificial fertilizers. The origin of most of the phosphorus is in the sea, in animals, algae and other creatures that exist at a depth of 100 m and more. The whales that feed on them there, defecate relatively close to the surface of the water, and from there the phosphorus reaches many marine creatures, including fish. Phosphorus reaches the land through fish that make their way from the sea to freshwater bodies, as well as with the help of seabirds that prey on fish. Eventually, the excreta and carcasses of animals that feed on fish (or seabirds), bring the phosphorus to the soil.

Unlike the large land mammals, whales were not exposed to the extinctions of our ancestors 20,000-10,000 years ago. However, in roughly the last 300 years, man attacked the giant marine mammals, and gave them names (an excellent opportunity to recommend the book "Moby Dick", which provides a glimpse of the golden age of whaling). It is estimated that the number of whales decreased by 70-90% during this period. This extermination, along with severe damage to the fish populations that move between saltwater and fresh water, the waterfowl and the terrestrial mammals, reduced the transfer of nutrients from the sea to the land on a huge scale. Researchers from the USA and Europe determine In a new study Because in the last 300 years the transfer of phosphorus by the whales has decreased from 340 million kg per year to only 75 million kg (less than a quarter!), and in total the transfer of phosphorus from the sea to the land has decreased by more than 90%!

We are missing

The huge decrease in the amount of available phosphorus is not just a theoretical danger. Poorer lands mean less vegetation, and this has many dire consequences: from global warming (forests are the main receivers of carbon dioxide, which helps warming), through deadly mudslides (in the absence of vegetation to stabilize the ground), to food shortages. Although today most of the agricultural areas are fertilized with artificial substances, but these are also produced with phosphorus that originates from the soil. Without these fertilizers, the danger of starvation hangs over all the inhabitants of the planet, but we don't have to wait for an apocalyptic scenario. It is enough for fertilizers to become more expensive at a certain rate to cause hunger and ignite food riots in large areas. The way to prevent the disaster is of course to reduce the extinction of whales and other animals. In recent years, efforts have been made to protect the animals, but it is not at all certain that these are sufficient to maintain the existing populations. Even with an extensive effort, it will take hundreds of years to return them to their previous levels. In any case, the message is clear: if we do not make a supreme effort to protect our planet, the future expected here - already in the coming generations, will be very bleak.