Every Snowflake Contains a Speck of Dust

The intricate, symmetrical beauty of a snowflake begins with a tiny imperfection. High in the atmosphere, water vapor requires a solid surface to latch onto in order to begin the process of crystallization. Without a microscopic anchor, these water molecules would remain as a supercooled gas or liquid, even at temperatures well below freezing. This essential anchor is known as a condensation nucleus, and it acts as the seed for every single snowflake that forms.

These nuclei are incredibly diverse and well-traveled. The core of a snowflake falling in your backyard could be a grain of dust from the Sahara Desert, a particle of ash from a distant volcano, a speck of soot from a wildfire, or even airborne bacteria. This particle is merely the starting point. As the initial ice crystal forms around it and begins its descent, its final, iconic six-sided shape is sculpted by the unique temperature and humidity conditions it encounters on its journey through the clouds, creating a frozen (Review) record of its atmospheric path.