Complex sentence: A micrometeorite is an extraterrestrial particle, ranging in size from 50 µm to 2 mm, usually found on the Earth's surface, and they are essentially micrometeoroids which have survived entry through the Earth's atmosphere.
Split into simpler sentences: A micrometeorite is an extraterrestrial particle, ranging in size from 50 µm to 2 mm, collected on the Earth's surface. Micrometeorites are micrometeoroids which have survived entry through the Earth's atmosphere.