Could the air we breathe today have once filled the lungs of dinosaurs?

Image source: Google

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Krishna: Not exactly the same air.

The composition has changed, the molecular structure has changed, although the atoms or other particles remain somewhat the same.

The oxygen levels in the atmosphere were much higher during the Cretaceous period, when dinosaurs lived, than they are today:

Cretaceous period: The oxygen levels in the Cretaceous period were up to 35%, compared to today's 21%. Today, oxygen makes up roughly 21 per cent of our air, but it was virtually non-existent in Earth’s early atmosphere.

Jurassic period: The oxygen levels in the Jurassic period were 26%, which is 130% of the modern level.

Between 850 and 600 million years ago, oxygen concentrations increased steadily from 2 to about 10 per cent: still not enough for humans to survive on. Fast forward to 400 million years ago and you could just about breathe but might feel dizzy and confused on about 16 per cent oxygen. Around 300 million years ago, oxygen levels reached a human-friendly 19 per cent and have not dropped below since (1).

Then the biochemistry of dinosaurs changed the molecular structure of the air once it got inside their bodies. The breathing biochemistry of dinosaurs varied depending on the species, but some dinosaurs had air sacs and lungs that worked together to make breathing efficient (2).

Image source: Shutterstock

When we inhale, oxygen from the air moves into the blood through the alveoli and capillaries. At the same time, carbon dioxide, a waste gas, moves from the blood into the alveoli and is exhaled when we breathe out. This process is called gas exchange. What we breathe in is not what we breathe out. So the composition changes.

Similarly what the dinosaurs breathed in would have a different composition to that of what they breathed out.

The atoms and molecules that came out of the dinosaurs must have undergone various reactions both in the atmosphere and in the forms they entered into as parts of.

So after millions of years you cannot expect exactly the same air to remain in the Earth’s atmosphere.

It must have changed over and over again.

Although the atoms and particles remain the same, they would have been recycled and presented to us in different composition and structures.

Footnotes:

1. How far back in time would we be able to go and still breathe our p...
2. Respiratory and reproductive paleophysiology of dinosaurs and early...