Hanika Rizo Chemical signatures in 3.7-billion-year-old basalt rocks from Greenland support the long-held theory that Earth was once almost entirely molten. We know very little about what early Earth looked like – but one theory says that at several times it was almost entirely molten, a magma ocean. These oceans were probably caused by a series of massive impacts with other objects in our solar system that each generated enough energy to melt our planet’s interior. One of the last such collisions is thought to have formed the moon. Advertisement Now, Helen Williams at the University of Cambridge and her colleagues have found evidence of these early magma oceans in ancient rocks.