Has Evolution Always Progressed at a Steady Rate?

The world is an exciting place these days, with a global economy, smart technology, and a vast array of fascinating plant and animal species. But it wasn't always such a fun place. In fact, for a long time -- roughly a billion years -- the Earth was dull as dishwater, with life stagnating at the level of slime. It all happened -- or rather, didn't -- between 800 million and 1.8 billion years ago, right in the middle of the process of evolution, which began approximately 3.5 billion years ago. During that middle stage, however, evolution stalled to the point that scientists sometimes refer to it as the "boring billion" years. Before that, evolution was pretty steady, if snail-paced, as single-cell organisms developed. But according to research, that progress stalled when the oceans ran low on trace metal nutrients, and ocean life -- which was all there was -- remained a slimy mess for around a billion years. Finally, over a 200-million-year span, the waters regained their life-giving nutrients, and evolution got back on track, ultimately leading to the biodiversity that we see today.

The Earth and evolution:

• Blue-eyed people were a rarity until a genetic mutation occurred approximately 10,000 years ago; currently, about 17 percent of the U.S. population has blue eyes.
• All of today's hundreds of dog breeds evolved from a single type of wolf.
• Contrary to popular belief, Charles Darwin stated that humans and apes shared a common ancestor, not that man evolved from apes.