Sometimes, a little perspective is a really helpful thing. For example, I’ve been feeling old lately. Maybe it’s just the winter, but I’ve been looking forward to bed by 9:00 pm. Last weekend I found myself thinking that I didn’t want to go out on Saturday night because it was Saturday night — the bars would be packed with all them youngsters! But there’s nothing like science to remind me that I’m still a young whipper-snapper, especially compared to the oldest fragment of Earth ever found.
Like so many other super-old life forms and fossils, this hunk of zircon was found in Western Australia. Scientists knew it was old, but their system of measuring just how old was inadequate. They used to count lead isotopes, but that process doesn’t work for zircons because the lead is moved around inside the zircon by the radioactive uranium inside. Instead, scientists used a new method called atom-probe tomography, which basically allows them to count each lead atom. And when they did that, they determined that the piece of zircon, along with two others they found, is 4.375 billion years old. What a geezer!
The zircon formed about 100 million years after the moon did. Because zircon crystals are made from water-rich materials, Earth may have had water on its surface back then, or at least cooled down fast enough after the collision that formed the moon to achieve a temperature that would have made that possible. We tend to think of Earth as uninhabitable, or at the very least an uninviting place back then, but this new finding suggests that may not be entirely accurate. Still, there was no internet back then, so it’s not like Earth was the most hospitable place either.
Zircon is one of the oldest and hardiest minerals around. These ones from Australia date back to the early days of Earth (relatively — we’re talking 165 million years after Earth was born, and Earth is about 4.54 billion years old) and have survived heating, intense pressure, tectonic movement, and the prying eyes of scientists. The minerals that comprise this zircon are thought to be about three billion years old, having eroded from the continental crust.
The new technique may put an end to scientific debates regarding the age of the rocks at the site in Australia, as well as other theories about the condition of early Earth. That is, so long as they’re not later exposed to be cleaning supplies.