So the Earth is, or was, a kind of giant balloon. We know seafloor spreading is still ongoing, and can affect global sea levels on historical timescales.
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Ancient fragments of Earth’s crust acted as ‘seeds’ for new crust to grow from, says LiveScience.
Around 3 billion years ago, Earth’s crust ballooned during a massive growth spurt, geoscientists have found.
At that time, just 1.5 billion years after Earth formed, the mantle — the layer of silicate rock between the crust and the outer core that was more active in the past — heated up, causing magma from that layer to ooze into fragments of older crust above it.
Those fragments acted as “seeds” for the growth of modern-day continents.