Age of the Seafloor at Mid-Ocean Ridges: Young & Renewing

The seafloor at mid-ocean ridges is the YOUNGEST on Earth—brand new, geologically speaking.

Why?

• Divergent Boundary: Tectonic plates pull apart.
• Upwelling Mantle: Decompression melting → basaltic magma rises.
• Eruption & Solidification: Lava erupts at ridge axis, cools instantly in seawater → **new oceanic crust (MORB - Mid-Ocean Ridge Basalt).**
• Conveyor Belt: New crust pushes older crust outward symmetrically. **Age = 0 at ridge axis; increases with distance.**

Age Progression

• Ridge Axis: 0 years (forming now).
• 10 km away: ~300,000 years (at 3 cm/yr half-rate).
• 100 km: ~3 million years.
• Oldest Oceanic Crust: ~200 million years (W. Pacific, E. Mediterranean) — then subducted.
• Continental Crust: Billions of years (not recycled).

Evidence

• **Magnetic Stripes:** Symmetric polarity reversals recorded in cooling lava — "tape recorder" of seafloor spreading.
• **Sediment Thickness:** Near zero at ridge; thickens with age.
• **Heat Flow:** Highest at ridge; decreases with age.
• **Seismicity:** Shallow quakes along ridge axis.

Mid-ocean ridges are **planetary crust factories**—the only places where Earth's surface is continuously *born*.