What made Earth a giant snowball 700M years ago? Scientists have an answer
Geoscientists have modeled the Sturtian “Snowball Earth” glaciation 700 million years ago, arguing it was triggered by a sharp drop in volcanic CO₂ outgassing combined with intense erosion that chemically drew down atmospheric carbon dioxide. Commenters use this to highlight how finely balanced Earth’s climate is, linking plate tectonics, the carbonate–silicate cycle, and solar output to long-term habitability and to possible filters in the Drake equation. The thread also spins off into speculative geoengineering and science-fiction scenarios—such as giant sunshades at L1 or Dyson-like structures—as thought experiments about deliberately pushing a planet into or out of extreme climate states.
Planet-Sized Sunshades and Alien Invasions
- Several comments explore a “low‑violence” way to take over a planet: parking a giant shade between planet and star to induce a snowball state, then later removing it.
- People debate feasibility:
- Shade could sit near the Sun–Earth L1 point but would need active station‑keeping due to orbital instability, radiation pressure, and solar wind.
- Estimates suggest enormous area (e.g., ~1% insolation cut → ~1M km² shade) and huge launch mass, but not obviously impossible for an advanced civilization.
- Proposals include very thin sails, swarms of “Sunjammer”-like panels, glitter/dust clouds, or pulverized asteroids; counterpoints note clumping, control difficulties, and astronomers hating the result.
- This setup is widely seen as strong SF fodder: aliens (or corporations/oil states/Bond villains) “cool the Earth to fix global warming,” then don’t turn it off; humans must respond.
Dyson Spheres and Detectability
- One commenter jokingly asserts we “know” civilizations can build Dyson spheres because some stars are missing; others call this out as baseless and humorous.
- Discussion clarifies that Dyson structures wouldn’t hide stars but re‑radiate in infrared, making them conspicuous; recent searches have not found convincing candidates.
Climate Sensitivity and Stability
- Thread notes that Snowball Earth episodes show climate can tip to extreme states, but over multimillion‑year timescales.
- Ice core and geologic data show large temperature swings (10–20°C) and past ice‑free greenhouse worlds; today’s “stable” climate is just a brief phase.
- Some argue this fragility is a major filter in the Drake equation and that our apparent stability may be observer selection: we only exist during habitable intervals.
- Others emphasize that even “small” Holocene shifts triggered collapses and extinctions; long‑term habitability is not guaranteed.
CO₂, Weathering, and Ice Ages
- Question: if low CO₂ can trigger ice ages, why rush to reduce it?
- Responses:
- Earth is currently far above the CO₂ level needed for a temperate climate; reducing today’s high levels is not remotely close to risking a snowball state.
- Distinction is made between stopping dangerous growth of CO₂ and actually pushing it low enough for global glaciation.
- Multiple comments explain the carbonate–silicate cycle:
- CO₂ dissolves in rain, chemically weathers silicate rocks, and ends up as carbonates in oceans; subduction and volcanism eventually return CO₂.
- Erosion of certain volcanic provinces can accelerate CO₂ drawdown, linking tectonics, weathering, and Snowball Earth events.
Media, Tools, and Meta
- Viewers recommend documentaries on Snowball Earth and Earth’s climate history, and a tectonics modeling tool (GPlates).
- Some lament modern web search quality, comparing it unfavorably to alternative engines.