Earth used to look like Mars. Here’s why that changed. | Robert Hazen

• I am a mineralogist. I love minerals, and they're so important in our lives. Virtually all the raw materials we use for technology, for our automobiles, for agriculture, indeed every living thing, depends on minerals. But what else? Minerals tell stories because they're incredibly information-rich.

Every mineral is a time capsule, and they tell us about the four and a half billion-year history of our planet. So we wouldn't be here, we wouldn't be able to talk about minerals if it weren't for the minerals themselves. Minerals were fundamental to the origin of life. There were all sorts of key steps, catalysis, reactance, protective surfaces that you couldn't have made life's chemistry without those special characteristics of minerals.

What we've learned—and this is astonishing— is that Earth has gone through these complete changes in character, in color. Earth started off as a black planet covered with basalt, and then the rains came and the oceans came and Earth transformed to a blue planet where it was covered by an ocean. Then we started plate tectonics, a process by which the near surface and the deep interior are churned in a way that creates gray continents of granite.

Life evolves to produce an oxygen-rich atmosphere that rusts the planet and you get a red planet now, much like Mars, but that's what our continents would've looked like 2 billion years ago. Then we went through periods of getting very hot and very cold. And in the coldest stages, we think the entire planet was covered by the white mineral, ice. The ice melted and the continents became green because life learned to live on land.

And so you now had to green planet, and you also had all kinds of biomineralization. We had shells and we had teeth and we had bones that showed the struggle for survival in life, but that struggle involved minerals as well. So for that entire four and a half billion history, we've seen the co-evolution of the geosphere and life—the abundant life we see on Earth today.