I read that iridium is a rare metallic element. It is found all over the Earth with fossils of dinosaurs. Where did it come from? — Evan of Sequim, WA

Dear Evan,

Like you said, Evan, iridium is very rare in the rocks of our planet. If you were to spread it around evenly, you would find no more than one pound for every 500,000 tons of the Earth's crust.

A few years ago, geologists discovered extra amounts of iridium in a band of clay sandwiched between two layers of rocks. They found very similar bands in other parts of the world. At that time, very few, if any, dinosaur fossils were found in the layers of rock above this band. Was there a connection between the iridium and the mysterious extinction of dinosaurs?

"Yes!," the scientists said. Certain types of meteorites have a lot of iridium compared to the Earth’s crust. Maybe a large meteor smashed into the ground, sending a cloud of dust (with the extra iridium) all over the Earth. This cloud blocked out the Sun, stopped the plants from making food, changed the climate, and killed off the dinosaurs.

Although this is a very popular story, no one knows why a big impact would wipe out the dinosaurs, and leave many other creatures untouched. In fact, creatures living in the sea seemed to have been affected the worst. Also, some fossil experts think that dinosaurs survived for quite a while after the impact.

There is no doubt that our planet has been hit by stray bits of rock in the past. As for extinctions, Noah’s flood is a better answer than meteors, because we know that it wiped out many of the creatures which were living at that time (Genesis 7:21-23). Exactly why the dinosaurs died out, while other creatures lived quite well, remains a mystery to this day.