Bombardment at 3.9 article

This excerpt from http://spaceflightnow.com article
on a spike in bombardment at 3.9bya.

Tiny melted fragments from the lunar rocks were dated at the noble gas
geochronology laboratory at Oregon State. Duncan and Huard were able to use
radiometric dating techniques to determine when the rocks had melted after being
struck by meteorites. What is particularly intriguing, Duncan says, is that this
apparent spike in meteorite activity took place about 3.8 to 4 billion years ago
- an era that roughly coincides with when scientists believe life first began
on Earth, as evidenced by the fossil record of primitive one-cell bacteria.

It is possible that life was introduced to Earth from one of these
meteorites, Duncan said. Or it could have developed spontaneously once the bombardment
subsided, or developed beneath the ocean near life-nurturing hydrothermal
vents. The lack of evidence on Earth makes the analysis of moon rocks much more
compelling. The meteorite activity that bombarded the moon likely struck our pla
net as well.

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