Published on May 10, 2018 Throughout Earth’s history, climate has varied greatly. For hundreds of millions of years, the planet had no polar ice caps. Without this ice, the sea level was 70 meters higher. At the other extreme, about 700 million years ago, Earth became almost entirely covered in ice, during an event known as “Snowball Earth.” What causes these swings in the planet’s climate? Lorraine Lisiecki investigates.