Research groups in Australia found the oldest mineral grains on Earth.
The oldest of these have ages between 4.4 and 4.5 billion years.
In an effort to further refine the age of Earth, scientists began to look outward.
The material that formed the solar system was a cloud of dust and gas that surrounded the young sun.
Samples returned from the Apollo and Luna missions revealed ages between 4.4 and 4.5 billion years, helping to constrain the age of Earth.
In addition to the large bodies of the solar system, scientists have also studied smaller rocky visitors to that fell to Earth. Some are cast off from other planets after violent collisions, while others are leftover chunks from the early solar system that never grew large enough to form a cohesive body.