Sep
26
2008

Oldest rocks on Earth?

Say you want to walk on the oldest rocks on the surface of the Earth. Well, it turns out that Canada is the place to go. Recently, Science magazine has reported that researchers have found rocks in Quebec that could be as old as 4.28 billion years old. Yes, billion. 4,280,000,000. Now, keep in mind that the Earth is estimated to be around 4.6 billion years old. There are at least three pretty neat points to make here:

1. It is harder than you think to find really old rocks, as most of the crust of the Earth is constantly recycling itself, courtesy of plate tectonics. Fortunately, there is not a great deal of tectonic activity happening in Canada, thus keeping these rocks at the surface.

2. 4.28 billion years old is pretty darn old. Think about it this way; this post is 2,129 characters long. That includes all of the letters and spaces. We will pretend that the very first characters of this post are the youngest, and the ones at the end are the oldest. Humans, which we will understand to be modern Homo sapiens, have only been around for approximately 40,000 years, which would be the very top of the "S" in "Say" that started this post. That is not even one full letter! These rocks have been around for all but the very last sentence of this post. That is a lot of characters/time.

3. They say that these could be the oldest rocks, as old as 4.28 billion years old, but... Dating of really, really old things like this use a technique known as radiometric dating. This type of dating does not give a specific date for the object in question, but rather, a range of dates. So these samples have dates ranging from 3.8 to 4.28 billion years old. The previously known oldest rock samples, also found in Canada, have dates that could be as old as 4.03 billion years old. So... these recently found rocks, if they are actually towards the younger end of their date range, could actually be younger than the potentially 4.03 billion years old rock that was already found.

No matter what, these rocks are still very exciting and can tell us some interesting things about the formation of the Earth's crust!

Your Comments, Thoughts, Questions, Ideas

bryan kennedy's picture

Great post! I really like your analogy about the age of these rocks. It's so hard for me to think about really large numbers like this without an example.

I ran across this gallery show the other day that used grains of rice to visualize different groups of the world population. It was called, Of All the People in the World. It would be fun to use this same method to represent geologic time. I wonder what 4.28 billion grains of rice would look like, compared to the pile rice grain representing the whole of human history.

posted on Fri, 09/26/2008 - 5:31pm
Julia's picture
Julia says:

That is an awesome way to visualize such large quantities! In checking with the U.S. Census Bureau, the current estimated population of the United States is a smidge over 300 million people. In looking at that huge pile of rice grains representing the United States, just think about a pile 14 times as big! Hmm, you could probably eat for quite a long time with the 4.28 billion grains of rice.

posted on Sat, 09/27/2008 - 12:24pm

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