Why Is Venus Hell and Earth an Eden? Author: Robin George Andrews Date: September 15, 2025 Tags: planetary science, climate models, climate science, physics, volcanoes, astronomy --- Overview Venus and Earth are planetary "twins" in terms of size, age, and origin, yet Venus is an extreme hellscape, while Earth is habitable. This puzzle drives scientists to understand why Venus turned hostile and what it implies about Earth’s future. --- Venus: A Hot, Acidic Hellscape Venus has a thick carbon dioxide atmosphere that creates crushing pressure. Sulfuric acid rains evaporate before reaching the surface due to extreme heat (hot enough to melt lead). Despite originating similarly to Earth, Venus' climate is hostile due to a runaway greenhouse effect. --- Leading Hypotheses on Venus’s Past Runaway Greenhouse from Hydrosphere Loss: Venus once had abundant water evidenced by heavy water vapor isotopes. Water vapor, a greenhouse gas, could have heated Venus dramatically. Early runaway greenhouse possibly triggered by the sun’s gradual brightening. Thick clouds on Venus’ slow-rotating dayside may have initially reflected sunlight, offsetting some warming. Volcanism’s Role: Large igneous provinces (LIPs) and volcanic eruptions released massive CO₂, intensifying warming. Venus likely experienced prolonged volcanic activity that boiled oceans away. Loss of water would hinder tectonic activity (subduction), preventing CO₂ sequestration. --- Earth's Climate and Carbon Regulation Earth’s climate regulation is linked to plate tectonics (subduction zones) that recycle carbon deep into the mantle. LIPs on Earth have caused intense warming but were followed by CO₂ being drawn back into the mantle. Plate tectonics and water presence enable Earth’s global thermostat and maintain habitability. --- Modeling Earth’s Fate: The "Reuniting Twins" Project A multidisciplinary model simulates Earth’s future conditions including solar brightening, volcanism, tectonics, and climate. Fast-forward 3.5 billion years: Sun’s brightness matches what Venus experienced at 1 billion years old. Model predicts: Earth’s oceans could evaporate, forming water vapor, enhancing greenhouse warming. Subduction zones could be inhibited due to lack of surface water, stopping CO₂ recycling. Tectonic activity would cease, creating a "stagnant lid" around Earth's mantle. Initial volcanic activity spike (~15 million years) would increase atmospheric CO₂. Afterwards, mantle cooling and crust thickening reduce volcanic CO₂ emissions. --- How Venusian Will Earth Be? Earth's atmosphere could rise in CO₂ from 0.04 bars to between 0.1 and 0.8 bars, pushing surface temperatures above boiling (~100 °C). This results in a "post-runaway greenhouse state" — boiling conditions unsuitable for life. However, Earth is unlikely to reach Venus’ current extreme of ~93 bars of CO₂ and crushing pressure. Earth might become a milder "Venus lite" due to mantle sealing and decreased volcanism. The model excludes rare mega-eruptions (LIPs), which if occur simultaneously might push Earth toward true Venusian conditions. --- Scientific Perspectives Experts appreciate the challenge to conventional thoughts about Venus and Earth’s divergence. The possibility that Earth won't reach Venus-level extremes provides an intriguing nuance. Uncertainty remains about future large volcanic events, which could alter Earth’s fate. --- Summary Venus and Earth started as similar planets but diverged dramatically. Venus became inhospitable through greenhouse runaway, possibly fueled by volcanism and loss of water. Earth’s plate tectonics and carbon cycling have so far prevented similar disaster. Models predict Earth may become extremely hot with high CO₂ millions of years from now but not as extreme as Venus today. Ongoing research aims to