
Did plants cause one of Earth’s great extinctions? - sea6ear
http://juneauempire.com/outdoors/2018-03-02/did-plants-cause-one-earth-s-great-extinctions
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nategri
> A more circular orbit of Earth around the sun — leading to years with no
> great difference between summer and winter — might have also helped doom
> most of the fish.

Oh man please do not say this without additional clarification. People are
confused enough as it is about what causes seasons.

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aaronblohowiak
For people who don't know -- earth's orbit is more like a circle than an
elipse. The tilt of the earth is responsible for most seasonal variation we
see on earth. IIRC, Mars has more of a difference between ahelion and
perihelion and that impacts seasonal variation there much more.

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mogigoma
The term here, if anyone wants to look into it, is "orbital eccentricity".
Here's a table listing the eccentricities of the various planets:
[http://www.enchantedlearning.com/subjects/astronomy/glossary...](http://www.enchantedlearning.com/subjects/astronomy/glossary/Eccentricity.shtml)

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cryptonector
The eccentricity of Earth's orbit doesn't make for more or less extreme
summer/winter differences, but more or less extreme northern vs. southern
hemisphere winter/summer differences. This is central to the theory of how the
Milankovitch cycles are tied to glacial and interglacial periods of the
current ice age.

What makes seasons less extreme is a closer-to-right-angle angle of the axis
of Earth's rotation to the ecliptic plane. This angle does vary a fair bit
over time.

In geologic time there are four astronomic parameters of Earth's movement, and
one for the Sun's, that can affect the climate and life:

    
    
         - eccentricity of Earth's orbit
         - precession of the equinoxes
         - angle of the axis of Earth's rotation to the ecliptic
         - distance from the Earth to the Sun (which, besides
           eccentricity, varies over long geologic time due to
           interactions with Jupiter and other planets)
    

When the northern hemisphere's summer coincides with the perigee of Earth's
orbit around the Sun, insolation is at its highest over the most landmass,
thus ensuring that ice does not accumulate on land over the summer and that
any existing ice melts. This is likely the cause of the start of
interglacials, while the opposite situation is likely the cause of the start
of glacial periods. The angle of the axis of Earth's rotation to the ecliptic
also plays a role, in this, obviously, since the smaller the angle the more
extreme the seasonal differences. So goes the theory anyways.

And, of course, the galactic neighborhood traversed by the Sun can make a
difference. We don't want to be near stars about to go supernova...

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jandrese
Seems like the culpret was a gigantic algae bloom using minerals liberated by
newly evolved land plants that were breaking up rocks with their roots. This
was exacerbated by poor ocean circulation from a highly circular orbit around
the sun (but what about the tilt?).

The same effect you get when fertilizer runs off into a stagnant pond or lake,
except on a global scale.

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chiefalchemist
And when this algae died it eventually became oil?

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mirimir
Increasing atmospheric oxygen from early photosynthetic organisms did drive
most anaerobes into extinction.

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pygy_
The Great Oxygenation Event.

Sounds like a fun party of massive death and extermination.

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mirimir
Botulinum and Clostridium get their revenge sometimes, however.

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cryptonector
Clostridium est dificil a batre.

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mirimir
Oui :)

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tzahola
>A more circular orbit of Earth around the sun — leading to years with no
great difference between summer and winter

I recognize quality science journalism when I see it! And I see here none.

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chiefalchemist
If correct (in some form), could this be used (in some way) to make Mars more
human-friendly?

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qbrass
It might help on a habitat scale, but won't help Mars on a planetary scale.
There's simply not enough atmosphere on Mars.

While CO2 makes up 95% of Mars's atmosphere and 0.04% of Earth's. There's
roughly the same amount of CO2 in the atmosphere of both planets. There's 500
times as much Oxygen in Earth's atmosphere than CO2. Even accounting for the
size difference between the planets, you'd still need hundreds of times more
oxygen than the current atmosphere could provide.

