What does it mean by the youngest religion? Is it the oldest or most recent (used today) religion?

Young religions, also called New religious movements (NRMs) are religions created recently, examples like LaVeyan Satanism (1966), Thelema ( early 1900s), Latter Day Saints (LDS / Mormons, 1820s), Jehovah's Witnesses (JWs, late 1870s), Discordianism (1963)

Older religions include Judaism and Hinduism, etc

"Most recent" is difficult to answer, but the largest religion today is Christianity with over 2 billion followers, followed by Islam and then irreligion.

a mid-ocean ridge or mid-oceanic ridge is an underwater mountain range, formed by plate tectonics. this uplifting of the ocean floor occurs when convection currents rise in the mantle beneath the oceanic crust and create magma where two tectonic plates meet at a divergent boundary.a geomagnetic reversal is a change in a planet's magnetic field such that the positions of magnetic north and magnetic south are interchanged.