Did plants cause one of Earth’s great extinctions? | Hacker News Reader

Did plants cause one of Earth’s great extinctions?

juneauempire.com

37 pointssea6ear19 comments

> 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.

Earth's orbital eccentricity has nothing at all to do with its seasons. It's nearly a perfect circle right now. The reason Earth has seasons is because of the axial tilt relative to the plane of rotation. In the northern summer, the northern hemisphere is angled towards the sun, and in the northern winter, it's angled away. This repeated incorrect claim in the article is frustrating, because it's otherwise describing a fascinating theory.

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.

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...

I found a couple of papers about correlations between Earth-orbit perturbations and ice ages; submitted separately:

https://news.ycombinator.com/item?id=16533837

It's sad that people who write such articles know so little science.

No, that's not at all a problem. The problem is how little they bother researching what they write about.

When you lack requisite background, research doesn't help very much. It's like cramming for finals, when you've done no work during the semester.

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...

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.

And when this algae died it eventually became oil?

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

The Great Oxygenation Event.

Sounds like a fun party of massive death and extermination.

Botulinum and Clostridium get their revenge sometimes, however.

Clostridium est dificil a batre.

Oui :)

>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.

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

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.

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