"We know that this feature was created by an asteroid impact about 4 billion years ago, but we were unsure how big this impact was and what effect it had on the moon." Several years ago ...

The team studied the mineral zircon from two of the oldest pieces of intact crust—dating 4.0 to 2.7 billion years old—and discovered that ancient plate tectonics, or how the continents move ...

These freshwater rocks were dated to around 3.4 billion years ago and to four billion years ago. The researchers concluded that the majority of water on Earth was salty, and four billion years ago ...