Blame it on “Snowball Earth.” The Earth’s crust is a visual timeline that goes back billions of years. But all over the world, there’s a gap in the timeline—a huge chunk of crust that should be there yet isn’t. Now, scientists say that the crust may have been destroyed during Snowball Earth, a hypothetical period in which the globe was covered in ice. The gap in Earth’s timeline is known as the Great Unconformity, and represents 250 million to 1.2 billion years of lost time. The crust timeline