4 mars 2016

Les 25 événements les plus déterminants

Le site BBC Earth nous offre sa liste des 25 événements les plus déterminants de l'histoire de notre planète.

Le site est très bien conçu et contient quelques belles animations, alors je vous recommande d'y jeter un coup d'oeil. Mais pour les curieux pressés, voici les 25 événements retenus:

4.5b years ago: EARTH IS BORN
Earth grew from a cloud of dust and rocks surrounding the young Sun.

4-3.5b years ago: THE ORIGIN OF LIFE
The oldest confirmed fossils, of single-celled microorganisms, are 3.5 billion years old.

3.4b years ago: LIFE HARNESSES THE POWER OF SUNLIGHT
Some of the early microorganisms evolved a way to use the energy from sunlight to make sugars out of simpler molecules.

3b years ago? : THE BEGINNING OF PLATE TECTONICS
Only when plate tectonics had come into operation could the first continent, nicknamed 'Ur', come into being.

2.4b years ago: THE GREAT OXIDATION EVENT
These microbes pumped out oxygen as a waste product, creating the oxygen-rich atmosphere we have today. 

2-1b years ago: ENDOSYMBIOSIS
Every animal and plant you've ever seen is a eukaryote.

1.2b years ago? : THE FIRST SEX
It's not clear why, or when, some organisms stopped simply dividing in two and started the messy business of sex.

1b years ago? : MULTICELLULAR LIFE
Now cells were teaming up to form larger organisms with things like mouths, limbs and sense organs.

850-635m years ago: SNOWBALL EARTH
This second Snowball period may have triggered the evolution of the first complex animals. 

535m years ago: THE CAMBRIAN EXPLOSION
In the Cambrian Explosion, it seems almost every group of modern animals appeared within tens of millions of years. 

465m years ago: PLANTS COLONISE THE LAND
The first land plants were relatives of green algae, but they rapidly diversified.

460-430m years ago: THE FIRST MASS EXTINCTION
Most life was still confined to the sea, and 85% of marine species were wiped out.

375m years ago: FISH THAT WALK ON LAND
Fish like Tiktaalik would eventually evolve four limbs, and give rise to amphibians, reptiles and mammals.

320m years ago: DAWN OF THE REPTILES
Unlike their ancestors they had tough, scaly skin and laid eggs with hard shells that did not have to be left in water.

300m years ago: PANGAEA
For the last time, all Earth's continents came together to form one giant supercontinent.

252m years ago: THE GREAT DYING
The Permian extinction was the worst mass extinction in the planet's history, obliterating up to 96% of marine species and similar numbers of land animals.

220m years ago: THE FIRST MAMMALS
Early mammals such as Morganucodon were small and shrew-like, and probably only active at night.

201m years ago: THE TRIASSIC EXTINCTION
We’re not sure what caused the Triassic extinction, but it killed off around 80% of species.

160m years ago: THE FIRST BIRDS
Birds evolved from feathered dinosaurs – modern birds are essentially Velociraptors with beaks instead of snouts and wings instead of arms.

130m years ago: FLOWERS FLOWER
Flowering plants only appeared in the middle of the dinosaur era. The equally-familiar grasses appeared even more recently.

65m years ago: DEATH OF THE DINOSAURS
Earth suffered its fifth and last mass extinction.

60-55m years ago: THE FIRST PRIMATES EVOLVE
The oldest known primate skeleton is of a species called Archicebus achilles, which weighed no more than 30 grams. 

32-25m years ago: SUPERCHARGED PLANTS
C4 photosynthesis is far more efficient than normal photosynthesis, allowing C4 plants to cope with harsh conditions. 

13-7m years ago: THE FIRST HOMININS
The oldest known hominid was Sahelanthropus tchadensis, which lived about 7 million years ago.

200,000 years ago: THE HUMAN RACE
Our activities have precipitated the sixth mass extinction and unleashed the fastest episode of climate change in Earth's history.



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