Development of Life
There is little doubt that one of the most important aspects of plate tectonics for humans is the crucial role it has played in the evolution of life on our planet. As mentioned in Chapter 2, many scientists now believe life may have originated around volcanic vents on the seafloor early in Earth’s history. One of the reasons for this that modern extremophile bacteria are found thriving in the hot gases and fluids discharging from seafloor vents along spreading centers. Whatever the exact origin, more complex life is known to have evolved and colonized the landmasses.
Once terrestrial (land) life was established, the combined effects of continental growth, continental drift, and evolutionary processes led to the great diversity and abundance of life-forms we see today. As you have learned in this chapter, subduction allows continents to grow at the expense of oceanic lithosphere, and mountain building creates various landforms at different elevations. The increase in land area over time then allowed terrestrial populations to increase, and the more varied landscape led to greater species diversification. Diversification was increased further when the supercontinent of Pangaea began to break up around 225 million years ago. As the fragmented landmasses began to drift apart, the terrestrial life-forms they contained were allowed to evolve in isolation, leading to even greater diversification (Case Study 4.1) The increased abundance and diversity of life resulting from plate tectonics proved to be of considerable importance when life had to reestablish itself after periodic mass-extinction events (Chapter 2). In the end, one can safety say that if it were not for plate tectonics, life as we know it would not exist.
FIGURE 4.29 The shifting position of continents affects Earth’s climate by altering the circulation of heat and water in the oceans. Climate is also affected by the uplift of mountains and by the rates at which heat-trapping gases are released by volcanic activity and absorbed in the rock cycle.