# Could modern man have breathed the air of the Cambrian era 500 millon years ago?

**URL:** <https://boards.straightdope.com/t/could-modern-man-have-breathed-the-air-of-the-cambrian-era-500-millon-years-ago/181939>\
**Category:** Factual Questions\
**Created:** [June 15, 2003, 1:38am UTC](https://boards.straightdope.com/t/could-modern-man-have-breathed-the-air-of-the-cambrian-era-500-millon-years-ago/181939 "2003-06-15T01:38:19Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![astro](https://avatars.discourse-cdn.com/v4/letter/a/9dc877/32.png) [@astro](https://boards.straightdope.com/u/astro)\
**Post date:** [June 15, 2003, 1:38am UTC](https://boards.straightdope.com/t/could-modern-man-have-breathed-the-air-of-the-cambrian-era-500-millon-years-ago/181939/1 "2003-06-15T01:38:19Z")

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Could modern humans have breathed the air 500 million years ago? Could modern fish have survived in the Cambrian seas?

Was the air and water substantially different than today or not?

[Cambrian Period](http://seaborg.nmu.edu/earth/Cambrian.html)

> [@](#):
>
> The Cambrian Period (from a Latin form of the Welsh name for Wales) begins the Paleozoic Era about 544 mya, and comes to a close about 510 mya. it was during the Cambrian that life “exploded,” developing almost all of the major groups in a relatively short time.
> 
> Originally, the bottom of the Cambrian was defined as the point where fossils began. Subsequently, older fossils have been found, and this definition is no longer valid. Now, it is roughly determined to be the point at which there is the first appearance of numerous fossil shells.

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**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\
**Post date:** [June 15, 2003, 1:44am UTC](https://boards.straightdope.com/t/could-modern-man-have-breathed-the-air-of-the-cambrian-era-500-millon-years-ago/181939/2 "2003-06-15T01:44:43Z")

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[probably.](http://globalchange.umich.edu/globalchange1/current/lectures/samson/evolution_atm/) The page doesn’t say, however, what other, possibly toxic, gasses may have been present at that time, however.

> [@](#):
>
> Sometime just before the Cambrian, atmospheric oxygen reached levels close enough to today’s to allow for the rapid evolution of the higher life forms. For the rest of geoogic time, the oxygen in the atmosphere has been maintained by the photosynthesis of the green plants of the world, much of it by green algae in the surface waters of the ocean.

Fixed link. – MEB

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**Author:** ![Squink](https://avatars.discourse-cdn.com/v4/letter/s/b5e925/32.png) [@Squink](https://boards.straightdope.com/u/Squink)\
**Post date:** [June 15, 2003, 2:21am UTC](https://boards.straightdope.com/t/could-modern-man-have-breathed-the-air-of-the-cambrian-era-500-millon-years-ago/181939/3 "2003-06-15T02:21:31Z")

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Atmospheric CO[sub]2[/sub] dropped below the toxic ~5% level about 1.5 billion years ago ([chart](http://www.scotese.com/precamb_chart.htm)), so you’d be likely be safe a mere 500 MyBP.