How the earth shaped us

Today, environmental issues have become a commonplace. The massive industrial activities of human beings and the consumption of natural resources have destroyed the global climate and caused the so-called sixth mass extinction. Therefore, the Nobel Prize winner in Chemistry, Dutch atmospheric chemist Paul Kruze, proposed that humanity is now in a new era of geology – the anthropocene. In other words, human beings are reshaping the earth.

However, compared to the long history of the earth’s history, our ability to shape the environment is only a phenomenon that has only recently emerged. For the most part, the environment has shaped humanity. The ever-changing physical characteristics of the earth have enabled humans to rise, exercise our extraordinary brains, help humans expand on the earth, and even promote the birth of the first cities.

So how does the Earth specifically do this?

High temperatures force mammals to evolve

Sixty-five million years ago, dinosaurs and most of the animals on the planet died together. The reasons for this are still controversial, or caused by the fall of meteorites, or by plate movement. However, a small number of survivors have survived, including birds, crocodiles and mammals. For a long time after the mass extinction, the Earth maintained a lower temperature. According to the fossil record, the evolution of the earliest human ancestor, the mammal, was not obvious during this time.

By about 55.5 million years ago, the temperature of the earth began to rise rapidly. In about 100,000 years, it has risen by 5 ° C to 8 ° C, and it has been maintained for a while, and it has fallen again. This high temperature period has brought great impact to different species. Scientists refer to this historic global warming as the “Paleocene-Eocene Extreme Thermal Event” (PETM).

Scientists believe that the cause of the extreme heat event is a series of volcanic eruptions. At first, the volcanic eruption spread carbon dioxide into the atmosphere, causing the temperature to rise to a certain extent, gradually melting the ice on the seabed. During the Eocene, as in the present, there are also a large amount of methane deposits on the seabed. When the ice melts, methane gas is quickly released into the atmosphere, causing the temperature to rise further rapidly.

The sweltering climate has led to the outbreak of species evolutionary diversity. Fossil records show that modern ungulates such as cattle, goats, pigs, sheep, camels and horses first appeared during this period.

In addition to ungulates, primate mammals also emerged in this global heat wave. These early human ancestors, similar to lemurs, spread rapidly to Asia, Europe, North America and East Africa after their first appearance. It is in the unique geological conditions of East Africa that they have taken the first step towards becoming human beings.

Water resources change makes people smarter

All animals need to find food and survive. For this need, animals respond to complex and rapidly changing environments in a timely manner, which requires intelligence and adaptability. It can be said that all animals have evolved to cope with the environment. Of course, human beings are no exception. The emergence of the human brain millions of years ago is a good example.

In fact, the arid environment in East Africa and the transformation of forests into the prairie are the main factors that led to the separation of ancient humans from primate ancestors.

In the dry equatorial region, rainfall varies with the Milankovitch cycle. The Milankovitch cycle is a theory put forward by the Yugoslav climatologist Milankovic. It means that the orbital shape of the earth moving around the sun, the tilt angle and the shaking of the Earth’s rotation axis are cyclical and affect the sunshine. The distribution at different latitudes causes changes in the Earth’s climate.

Although the time scale involved in the Milankovitch cycle is usually very long, combined with the special geographical structure of the Great Rift Valley, the ridges on both sides of the rift block the movement of moist clouds, making the lake at the bottom of the rift water The changes are very sensitive, and the climate in East Africa has produced dramatic changes in extreme dryness and extreme humidity in just 20,000 years. During the wet period, the lake has a very high water level, and during the dry period, the lake forms sand dunes. The ever-changing supply of water, the environment that causes a dramatic shift between famine and food abundance, can survive for people with larger brain capacity.

The study found that the period of three extreme climate changes coincided with the evolution of the human brain. The first occurred 2.6 million years ago, when residents of the Great Rift Valley were forced to migrate to South Africa, and erect monks appeared. The second occurred 1.9 million years ago, Homo erectus appeared in Africa and migrated to Asia. The third occurred 1 million years ago, and Heidelberg people appeared. At every stage, brain capacity has increased. When an unstable, fluctuating environment encourages the growth of intelligence, humans gradually learn to use social interaction, language, and tools.

Cold promotes human migration

Our ancestors did not stay in the cradle of their birth, but tried to find a more suitable living environment. They crossed the ocean separating the mainland and gradually conquered the world.

Modern humans left Africa about 65,000 years ago and moved to Europe and today’s India and Southeast Asia along the southern edge of Eurasia. During this period of great migration, the Earth was in a severe ice age, and the huge ice sheet locked a large amount of water, causing the global sea level to drop by 120 meters.

A large shallow continental shelf (the extension of the continental coastal land below the sea to the ocean) emerges as a land and land bridge. Asia’s Indochina is connected to Malaysia, as well as to Sumatra, Java and other parts of Indonesia, and there is now land between New Guinea and Australia. In particular, a land corridor between Siberia and the Bering Strait of Alaska provides a route for our ancestors to enter the North American continent from Eurasia. On the North American continent, they quickly crossed the Isthmus of Panama and reached South America.

Early humans in Europe and Central Asia met cousins ​​Neanderthals and Denisovars and acquired a portion of their genes. Later, some people stayed in the Eurasian continent, while others continued to move forward to the American continent where no one had ever set foot.

Stable climate fosters civilization

Beginning around 115,000 years ago, people around the world began to abandon the lifestyle of hunting and collecting food, settled down, and gave birth to human civilizations that have been inherited today.

In the past few thousand years, as the earth’s climate has become drier and colder, cereal crops such as wheat, rice, and corn have spread all over the world, and hoofed herbivores have long dominated the grassland ecosystem. People quickly learned to tame these wild animals and grow cereal crops. Settled life based on agricultural production has led to rapid population growth. Soon, people began to gather together to form an organization of a certain size, and further formed a city.

Today, the position between the Earth and humans has reversed. The climate change caused by human activities is the most serious change in global temperature since the 55 million years ago. Early climate variability is critical to the development of our ancestors, but today’s similar events will have disastrous consequences for our current production and lifestyle. For example, some areas are becoming more and more arid, fertile soils are gradually losing, while others are being hit by heavy rains and floods, and extreme conditions can undermine agricultural development. The melting of polar ice caps will lead to sea level rise and the risk of flooding coastal areas and cities.

For the future of mankind, we must understand the deep connection between man and earth, understand how the earth has shaped us, respect and cherish everything we have now. If we continue to undermine the Earth’s environment, human-driven climate change will shape our future as the Earth itself shapes our past.