Life

A history lasting millions of years

The history of the Earth is divided into five ages: Archaeozoic or Precambrian, Palaeozoic or Primary, Mesozoic or Secondary, Cainozoic or Tertiary, Neozoic or Quaternary.
Archaeozoic age
The Archeaozoic age is the longest one: it began 4.6 billion years ago and ended 530 million years ago. 3 billion-year-old fossils prove that the oldest organisms known so far are very simple, heterotrophic unicellular algae. Some green-blue autotrophic algae appeared, however, approximately two billion years; they could produce the nutrients they needed by themselves, through the photosynthesis. This process caused oxygen to spread from the sea to the atmosphere, thus leading to the appearance of more complex organisms that would conquer the Earth’s surface.
The Palaeozoic age
The Palaeozoic age is called the age of “manifest life” and spans across 285 million years, from 530 million years ago to 245 million years ago. A high number of events occurred over this period. Many animal and vegetal groups made their first appearance, many of which disappeared during the same age. At the dawn of the Palaeozoic age, life existed only inside or near oceans. The most common living beings were trilobites, crustaceans, corals and some primitive types of fish. Plants were the first forms of life to spread on the mainland. Huge marshy forests developed, that over the years originated the large deposits of fossil coals that are currently exploited as en energy source. The Palaeozoic age is also known as the age of the great extinctions: at some point, approximately 95% of all the living beings of the Earth disappeared. This event was probably caused by deep climatic changes and powerful volcanic eruptions. The Mesozoic age
Mesozoic age lasts 180 million years, from 245 million years ago to 65 million years ago. Mesozoic means “mid-life”. The living organisms were actually not as primitive as in the Palaeozoic age, but were not too developed either. It is the so-called “reptilian age” because of the appearance (and disappearance) of dinosaurs. The most common vegetal organisms were trees and plants with seeds and flowers. The warm climate boosted a huge spreading of the flora, that supplied dinosaurs with large amounts of food.
The Cainozoic age
The Cainozoic age ranges from 65 million years ago to 2 million years ago and corresponds to the age of Mammals. Actually, as the big reptilians disappeared, forests and plains were invaded by these animals. The flora and fauna began to look as they do today.
The Neozoic age
The Neozoic age (which means “new life”), the age in which we live. It is in this age, which is still young compared to the earlier ones, that man made his appearance. Man has soon learnt to grow and exploit plants for his needs, to obtain more and more productive species through cross-breeding, and recently also to manipulate them genetically to artificially create plants with specific characteristics.