A great part of Britain's identity is wrapped up in the fact that it's a part of Europe, but it stands apart, quite literally, as an island. According to new sonar studies of the Channel which runs between Britain and France, that wasn't always the case. Until about 200,000 years ago, Britain was a peninsula of Europe, and could be walked to from mainland France -- as many early humans did. So what severed the soil? An almost unimaginably huge flood, possibly triggered by a small earthquake, pushed a giant, river-fed lake through the narrow isthmus which once stood where the English Channel now flows; then, the proverbial dam broke. At its peak, the flood may have discharged up to a million cubic meters of water per second, making it one of the most significant known megafloods in the Earth's history.