Title:

Discovery that nanophase Magnetite controls Ice nucleation in Nature:

Implications for the climate control, human food supply, and possibly the origin of life.

Speaker: Dr. Atsuko Kobayashi (ELSI)

Abstract:

In supercooled water, ice nucleation is a stochastic process that requires ~ 250-300 molecules to transiently achieve structural ordering before a seed crystal can nucleate; this happens most easily via alignment on crystalline surfaces like mineral dust particles, a process termed heterogeneous nucleation. Without such nucleation sites, water will supercool to below -30 ̊C before the rate of Brownian motion decreases to the point where the competing process of spontaneous, homogeneous nucleation is favored. Major efforts in the climate and food- processing communities have focused on identifying the best materials for controlling heterogeneous ice nucleation, and have identified silver iodide (used in commercial cloud seeding), some bacterial proteins, and k-feldspar in mineral dust as the leading materials.

However, in the process of trying to develop better cryofixation techniques for TEM, I discovered that nanocrystals of magnetite provide one of the most potent sites for ice crystal nucleation in the natural environment, many orders of magnitude better than that of any other mineral yet tested. In fact, natural feldspars often contain ppm levels of magnetite nanocrystals, which may explain the elevated nucleation rate on feldspar. Because magnetite nanocrystals are widespread in the terrestrial environment, they may control Earth's climate cycle rather than feldspar. Similarly, biological magnetite are present in almost all plant and animal tissues, and may be responsible for the ice and frost damage that destroys up to 40% of the human food supply. I also discovered that ice formed from supercooled water expands significantly less than that which freezes near 0 ̊C, and lacks the needle-shaped crystal habit that breaks cell walls during freezing. Hence, technology that controls or eliminates these magnetite nanocrystals during freezing could enhance the human food supply.

For the origin of life, ice freezing formation can concentrate prebiotic molecules like RNA and amino acid at the crystal surface in an environment rich in mineral dusts containing magnetite. I want to understand from a fundamental level the process of ice crystal nucleation, which can help constrain the environments in which ice might have formed on the early earth. Without nucleation sites, water will supercool, and when it eventually does freeze it is not as efficient at concentrating prebiotic chemicals.