Seafloor Ages and Plate Tectonics
Aligned to HS-ESS1-5 — Next Generation Science Standards.
What this lesson teaches
New ocean crust forms at mid-ocean ridges and spreads outward, so the seafloor is youngest at the ridge and oldest near continents. This pattern is direct evidence that plates move and that crust is created and destroyed over time.
Worked example
Rock sampled at the Mid-Atlantic Ridge is nearly zero years old, but crust near the North American coast is about 180 million years old. The steady increase in age with distance from the ridge shows the Atlantic Ocean has been slowly widening.
Practice questions
- Observe: Ocean crust is nowhere older than about 200 million years, yet continental rock can be billions of years old. What does that contrast tell you?
- Model: Draw a mid-ocean ridge with age labels on the seafloor to show how it grows symmetrically on both sides.
- Explain: Given that the seafloor is young everywhere while continents are ancient, argue what must be happening to old ocean crust.
Watch the lesson
Every lesson comes with a video taught in English and Spanish — the same video the QR code in the printed workbook opens.
▶ Watch this lessonEn español
Edad del fondo marino y tectónica
La corteza oceánica nueva se forma en las dorsales oceánicas y se expande hacia afuera, así que el fondo marino es más joven en la dorsal y más antiguo cerca de los continentes. Este patrón es evidencia directa de que las placas se mueven y de que la corteza se crea y destruye con el tiempo.
Ejemplo: La roca tomada en la dorsal mesoatlántica tiene casi cero años, pero la corteza cerca de la costa de Norteamérica tiene unos 180 millones de años. El aumento constante de la edad con la distancia a la dorsal muestra que el océano Atlántico se ha ensanchado lentamente.
More Space Systems lessons
Teach this lesson today
An AI tutor that guides with questions instead of just giving answers — all K–12 core subjects, every child in the family.
Start free — no card required