Re: Moon crater survey and impact dating

While there does seem to be some periodicity associated with extinctions on Earth (1), there is little to no evidence (so far) that they were caused by impacts and even less evidence that they were caused by "Nemesis" (1). In fact, only 1 extinction episode (dinosaurs; the KT boundary) has been linked to an impact (2), and even that is still under scrutiny (3). The massive extinction event at the PT boundary has also been linked to an asteroid or a comet (4), but again, evidence is controversial (5).

Several craters on the moon have been dated; in fact, we see lots of impact ages over the course of the Moon's history (4.52 billion years). So far, no impact ages other than the one at 3.9 billion years ago (6,7) dominate the lunar samples. So, no. No evidence of impact periodicity has been observed in the lunar samples and craters.

The Moon has an ancient magnetic field (8, 9), but its orgin is still unknown (10). Since magnetic fields are linked to the activity of the core of a planetary body, magnetism fades once the core solidifies. Therefore, I see no reason for there to be a relationship between the Moon's ancient magnetic field and Earth's current magnetic field.

For more on the Moon, check out The Nine Planets Web site.

1. Nemesis: Does the Sun Have a "Companion"?

2. Chicxulub and the Cretaceous-Tertiary Boundary

3. The KT Extinction

4. Scientists Find the "Trigger" For The Largest Mass Extinction on Earth

5. Volcanic "Flood" Linked to Extinction

6. Uranus, Neptune, and the Mountains of the Moon

7. Lunar Cataclysm

8. On the Source of the Ancient Lunar Magnetic Field

9. New Model Explains Lunar Magnetism

10. Constraints on the Origin of Lunar Crustal Magnetism