Moon-Forming Giant Impact
c. 4.5 Billion years ago · Prehistoric
Approximately 4.5 billion years ago, a Mars-sized planetary body called Theia collided with early Earth. The impact ejected debris into Earth's orbit, which coalesced to form the Moon. The collision altered Earth's composition and rotation, stripped away much of Earth's early atmosphere, and caused extensive surface melting. The Moon's gravitational influence later stabilized Earth's axial tilt, contributing to stable climate conditions. Reginald Daly proposed the original impact theory, while William K. Hartmann and Donald R. Davis developed the modern version.
Key Figures
Reginald DalyWilliam K. HartmannDonald R. DavisAlex N. Halliday
Locations
MoonEarly EarthTheia
Topics
planetary formationearly Earthsolar systemimpact events
Connected Events — 3 Connections
The Moon-forming impact created Earth-Moon system dynamics that influenced the orbital mechanics and gravitational perturbations affecting asteroid trajectories during the subsequent Late Heavy Bombardment period Late Heavy Bombardment
Stellar nucleosynthesis in first-generation stars created the heavy elements like iron and silicon that composed both Earth and the Mars-sized impactor Theia, making the Moon-forming collision chemically possible First Heavy Elements: Birth of Stellar Nucleosynthesis
The Theia impact vaporized any earlier water and resurfaced the planet in magma; the Hadean ocean formed only after Earth re-cooled over the following 100-150 million years Earth's Hadean Ocean Condenses from Volcanic Outgassing
The Time Detectives® · Cadet Mission
Investigate This Event
Place it on the timeline. Earn points. Master the connections.
New to The Time Detectives?
Learn what it is →