Over the weekend, at the Earth Day tweetup at the Science Museum of Minnesota, I heard an interesting fact: Human beings are now the dominant agent of landscape change on this planet, more than any natural process. (That's right. Suck it, glaciers!)
We tend to think of this kind of thing as a result of modernity. But I think that's only partly true. Modern technology has given us the tools that enable us to change the landscape of Earth in massive ways we weren't capable of in the past. But throughout human existence—even before we were technically human—we have made relatively large alterations to the world. It's not like human beings woke up one day and thought, "Hey, it's the 20th century, let's start messing around with stuff!" In reality, what makes our modern impact on the planet different from past—other than scale—is mainly that we've developed more self-awareness about our impact on the planet, and have actually started talking about whether we like the side effects those impacts bring.
Case in point: A recent study of ancient African animal species that suggests our ancestors drove a huge proportion of fauna to extinction basically as soon as they were technologically capable of doing so. Here's how Ann Gibbons described it at Science Now:
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After comparing fossils of 78 species of carnivores that lived during five different periods of time between 3.5 million years ago (when large carnivores were at their peak) and 1.5 million years ago, Werdelin found that all but six of 29 species of large carnivores (animals that weighed more than 21.5 kilos) had gone extinct in that time.