Clouds May Hold Key to Why Early Earth Didn’t Freeze Over A
paradox about the climate of the early Earth that has been
plaguing scientists for nearly 50 years may have a new solution.
The so-called 'young' sun paradox — first proposed by Carl Sagan
and his colleague George Mullen in 1972 — refers to the fact
that the Earth had liquid oceans for the first half of its more
than 4-billion-year existence despite the fact that the sun was
likely only 70 percent as bright in its youth as it is now. A
lower solar luminosity should have left Earth's oceans frozen
over, but there is ample evidence in the Earth's geological
record that there was liquid water — and life — on the planet at
the time. Over the past few decades, scientists have proposed
several possible mechanisms that may have kept the Earth toasty
enough to keep water from freezing during our planet's early
history – a period of time called the Archaean. But just when
scientists think they have the paradox solved, other researchers
come up with alternate