Question 1

Take a deep breath

Accepted Answer

Around 4.5 and 4.4 billion years ago, as the Earth was forming, there was  no oxygen (O₂) in the atmosphere. Until 850 million years BP, oxygen concentration remained below 5 % because it was almost immediately captured by the  iron - rich rocks it would oxide. O₂ levels  will rise gradually. Around 540 million years, when the Cambrian explosion unfolds, oxygen accounts for 15 - 20 %  of the atmosphere.  Peak level  – 35% – is achieved at the end of the  Carboniferous, about 300 million years BP. This exceptional ratio is due to the existence of the vast forests that are behind  the creation of coal deposits. These  high O₂ levels might have also enabled the emerging of giant invertebrates, such as Meganeura, a dragonfly with a wingspan of 80 cm, or Arthropleura, a centipede that could measure up to 2 - 3 meters in length.Nowadays, the Earth's atmosphere contains about 21% oxygen.

Question 2

Funfact | A life with no oxygen

Accepted Answer

The anaerobes - micro-organisms to which oxygen is toxic - are still with us today. They have settled down in nice little places deprived of oxygen, such as deep-sea sediments, swamp beds, or your gut, where anaerobic bacteria  like Clostridium, Bacteroides or Methanobrevibacter thrive.

Question 3

Funfact | The anaerobes

Accepted Answer

have a crucial part in the degradation of organic matter,  fermentation and methane production.

Question 4

Funfact | Fizzy water

Accepted Answer

Still to this day, we fight some of the descendants of anaerobic bacteria by disinfecting wounds with hydrogen peroxide.

Question 5

Atmosphere, atmosphere, atmosphere

Accepted Answer

There are three types of atmospheres. The primary ones, found on massive planets such as  Jupiter, derive from the original gas retained by gravity. The secondary ones, typical of terrestrial planets,  form by way of  volcanic activity, outgassing  or comet impacts.The tertiary atmosphere is a secondary atmosphere transformed by living organisms. Which is the case  – unique to our knowledge to date – of the Earth, where cyanobacteria were the first to enrich ambient air with oxygen.

Atmosphere, atmosphere!

All living creatures do not have the same needs in terms of atmosphere. 2,4 billion years ago, the composition of the Earth's atmosphere changed profoundly. To our greatest benefit - and at the detriment of the anaerobes, which cannot survive when exposed to oxygen.

Informations complémentaires

Take a deep breath

Funfact | A life with no oxygen

Funfact | The anaerobes

Funfact | Fizzy water

Atmosphere, atmosphere, atmosphere

Continue your journey