Venus versus Earth: Why one World boils and one blooms

Venus shines brightly in the night sky, but up close it is a furnace. Its surface bakes under crushing pressure and acid-filled clouds, leaving scientists with a haunting question. If Venus and Earth were born alike, why did their paths diverge so sharply?

Did Venus once resemble Earth?
Venus and Earth formed at the same time and share similar size and composition. Yet Venus is cloaked in carbon dioxide, with temperatures hot enough to melt lead. Evidence suggests water once flowed there, raising questions about what destroyed it. Studies show rare heavy water molecules in Venus’ atmosphere, hinting at vast ancient oceans. But did the sun’s growing heat boil them away, or did violent volcanic events trigger the runaway greenhouse effect?

Was the sun or volcanism to blame?
Some researchers argue the brightening sun could have evaporated oceans, filling the sky with water vapour and heating the world. But models suggest Venus’ slow rotation might have created thick reflective clouds, preventing such a quick collapse. Many now believe colossal volcanic eruptions released massive amounts of carbon dioxide, driving the planet into climate chaos. With no oceans to absorb gases, subduction halted, and Venus lost its thermostat.

Could Earth share the same fate?
Scientists are testing Earth’s limits through the Reuniting Twins project. By digitally fast-forwarding Earth’s climate billions of years, they ask if our planet could follow Venus. Their simulations show that in 3.5 billion years, rising sunlight could evaporate oceans, halting subduction and unleashing heat-trapping gases. Earth could become unbearably hot but likely “Venus lite”, with conditions less extreme than Venus.