“Two great tastes that taste great together!” So goes the tagline for Reese’s Peanut Butter Cups. The first ingredient—chocolate—provides the sweet, rich taste. The second—peanut butter—adds a dense, salty kick. Together, they do indeed taste great.
And just like you need chocolate and peanut butter to make a Reese’s, so you need liquid water and plate tectonics to make a habitable planet.
Virtually everyone agrees that a habitable planet hosts an abundance of liquid water—the chemical reactions necessary for life require it. Research also shows that plate tectonic activity plays an important role in sustaining a planet’s liquid water. Studies of Earth’s history demonstrate that a diverse set of circumstances and mechanisms maintain the vital tectonic activity. And scientists continue to gain an even better understanding of the intricate processes that helped Earth sustain a healthy level of tectonic activity over billions of years.
As plates move across Earth’s surface, new plate material forms along some boundaries and at other boundaries one plate will dive under another in a process called subduction. Today, subduction happens as the young plate material moves away from hot ridges and cools. Eventually it cools to the point where it no longer floats on top of the less dense mantle and begins to sink.
Early Earth’s interior and mantle were too warm for this process to occur regularly. However, recent research shows that a different mechanism operated to maintain a healthy level of tectonic activity. Continental material forming and accumulating in the middle regions of the plates caused the plates to spread horizontally and push on the adjacent plates. Eventually one of the plates would push under another, thus starting the process of subduction. As time progressed, Earth continued to cool until the point where the cold plate edges would spontaneously sink into the underlying mantle.1
Plate tectonics has operated on Earth for at least the last three billion years—yet the planet has experienced enormous changes throughout this time. The Sun’s luminosity was previously 20–30 percent lower. The planet began with virtually no atmospheric oxygen and now oxygen makes up roughly 20 percent of the atmosphere. Once there were no continents; now they cover almost 30 percent of the planet surface. Life’s history began with relatively simple, single-celled life and now includes a great diversity of birds, mammals, fish, bacteria, and many other kinds of life.
These changes demonstrate a remarkable match to the description given in Genesis 1. The fact that plate tectonics operated throughout these changes and Earth’s surface remained covered in liquid water point to an intelligence that ensured the planet’s habitability while orchestrating all the necessary changes for humanity to survive and thrive.