Life on Earth

While browsing in a library, a children's book, a comic book, caught my eye. It talked about our Earth and life, on the continents, in the seas, and in the air.
I was surprised by an image depicting men, admittedly dressed in animal skins, hunting dinosaurs. How can we allow the idea to creep into the minds of our children that these two living species could have coexisted?
Let's briefly recall these periods when Earth was home to these two "colonizers," dinosaurs and humans.

Scientists place the creation of the Universe, the Big Bang, around 13.5 billion years ago.

Our solar system, including Earth, was born a little less than 5 billion years ago, to round off the figures.

We have to go back a little over 500 million years to see the Earth begin to show signs of life. Jellyfish and fish began to populate the seas. Then, on the continents, lichens and plants colonized the land.
Next came mammals and dinosaurs at the end of the Paleozoic Era, 250 million years ago.

The impact of a meteorite 10 km in diameter in the ocean off the coast of Mexico likely caused a cooling of the Earth's climate some 65 million years ago, at the end of the Cretaceous Period, which led to the extinction of the dinosaurs. Scientists are almost certain of this, with supporting evidence. But this very real cooling could also be explained by other causes: a massive volcanic eruption or the uplift of previously submerged land.

At the time, an entire segment of the fauna perished with them, joining the ranks of extinct species.

We also know that around the time of this extinction, the Earth cooled overall. Scientists therefore believe there is a strong link between these two phenomena: the cooling seems to be the key to the enigma. But this leads to another enigma: what caused this abrupt climate change?
In 1980, an American scientist, Luis Alvarez, dropped a bombshell: he analyzed samples of terrestrial soil dating back 65 million years, all of which showed a high concentration of a chemical element, iridium. This element is rather rare on Earth, but abundant in certain meteorites. From there, it was a short step to thinking that the iridium found in the soil was of "extraterrestrial" origin, a step Alvarez took.

According to him, 65 million years ago, a meteorite with an estimated diameter of 10 km crashed into Earth on the Yucatan Peninsula near Chicxulub. Scientists have discovered a fossil crater 200 km in diameter that could correspond to the impact site.
This impact, which occurred at 90,000 km/h, is estimated to have released energy equivalent to 5 billion Hiroshima-type atomic bombs. The impact pulverized rocks and projected tons and tons of ash throughout the Earth's atmosphere. This ash darkened the sky, preventing the Sun's rays from warming the Earth. As a result, a very long winter of approximately 800 years descended upon our planet, cooling it down. Perhaps too fragile, the dinosaurs and some other species then perished. This "killer meteorite" hypothesis is the one favored by astronomers. But some scientists suggest other events that could have altered the climate, such as the ashfall from a major volcanic eruption or the upwelling of submerged land that disrupted ocean currents. Who knows, perhaps these causes combined?

Homo sapiens, in other words, humans as we know them today, appeared on Earth some 300,000 years ago.

This figure might seem staggering compared to the length of a human lifespan. Indeed, since the day the first human appeared, some 20,000 generations of humans have succeeded one another on the surface of our planet. But what do all these generations really represent in relation to the age of the Earth or, even better, the Universe and its 14 billion years of existence? A featherweight…
Over millennia, humankind has tamed its space, colonized the planet, and gazed ever further into the cosmos. Today, we build telescopes that allow us to assess the age and evolution of the Universe.

But from these observations emerges a damning truth: in terms of time, humanity's cycle in the cosmos is a negligible quantity.
Let's follow the significant events from the birth of the universe to the present day as if they had unfolded in a single year, from January 1st at midnight until December 31st at midnight.
Where did humankind first appear? In June, in July?
January 1st at midnight the Universe was reborn from a gigantic explosion, "the Big Bang." Between the end of January and the end of February, our galaxy, the Milky Way, as well as other galaxies, formed until August, and within our galaxy, stars were born and exploded, and others appeared. At the heart of this cosmic ballet, the matter from which humankind will be made is slowly being formed.
On August 29, a small, unremarkable star, the Sun, ignites. It is surrounded by a corona of gas and dust that clump together to form the planets, including Earth.
It will be another few days until mid-September before the very first living beings, bacteria called "blue-green algae," teem on the planet. Fish appear on December 18, and mammals on the night of December 27-28. The hominid, the oldest known to date, is not born until December 31 around 7:30 p.m. But it is only a quarter of an hour before the end of the year, at 11:45 p.m. on December 31, that Homo sapiens makes its entrance onto the Earth's stage. Along with the great apes, its cousins, Homo sapiens shares the same grandparents, but not the same parents. When the common branch Did the universe split in two: the great apes on one side, and the hominids, ancestors of humans, on the other?
For a long time, it was believed that the famous Lucy, approximately 3 million years old and discovered in Ethiopia in 1974 by a team including the Frenchman Yves Coppens, was the first hominid in history.

But in 2001, the skull of an even more distant ancestor, it seems, was discovered in northern Chad. Named Toumaï, it is nearly 7 million years old. Will we find anything even older?

Let's return to our cosmic scale, which consists of reducing the age of the Universe to 1 year and placing events on it proportionally.
Our Earth will not survive beyond May 10th of next year, because the Sun, like all stars, will have grown so large that it will absorb the Earth. by having vaporized it a little beforehand. As a result, no living being on our Earth will take a selfie of the Sun's explosion.
The explosion of stars is a spectacle to which humankind is invited. They are rare but always thrill astronomers. In 1054, the Chinese were able to admire, for 21 days, a flash in the sky: the explosion of a supernova. Today, when we turn our telescopes towards this point, at the tip of the horn of Taurus, we have this magnificent image that concludes the article.

We could also spend our long winter nights by the fireside, talking about the future of our planet, about its mistreatment by humankind. If we continue down this path, which is nothing but a dead end, the last living species to arrive on Earth could be the first to disappear completely. Where has human intelligence gone? A sad observation.