How Do Scientists Play the Dating Game?
2009 June 7. Early
rocks to reveal their ages.
By Jennifer Carpenter, BBC News. Excerpt:
A new technique has been helping scientists
piece together how the Earth's continents were
arranged 2.5 billion years ago.
The novel method allows scientists to recover
rare minerals from rocks.
By analysing the composition of these minerals,
researchers can precisely date ancient volcanic
rocks for the first time.
By aligning rocks that have a similar age and
orientation, the early landmasses can be pieced
...Analysis of rocks that formed when continents
drifted apart can help geologists reconstruct
Dr Richard Ernst, a geologist from the University
of Ottawa, explained that molten magma fills
the cracks formed by shifting continental plates.
The magma cools to form long veins of basalt
- a volcanic rock - that has a "distinct
magnetic signature" revealing the rock's
orientation and latitude when it formed.
By combining this "magnetic signature" with
the ages of these rocks, researchers can tell
whether rocks on different continents were once
part of the same volcanic up-welling.
But until now, researchers have been unable
to determine the ages of many of these ancient
rocks because of the difficulty in extracting
the minerals used to date them.
"We are dealing with such small mineral
crystals - typically much less than 100 microns
long - we are talking about grains far smaller
than the width of a human hair," explained
Dr Michael Hamilton, a geologist and co-leader
on the project.
But with the development of new techniques,
minerals - such as baddeleyite - can now be
Baddeleyite is useful because it incorporates
large amounts of uranium into its crystal-structure,
and because uranium naturally decays to lead.
Scientists also know the rate at which this
"[They] can use these minerals as radioactive
clocks," Dr Hamilton added. "All we
need to do is measure the the amounts of uranium
and lead very precisely."...
1998 September 22. How
Old are the Rocks? Using
Radioactivity to Find Out. When a volcanic
magma cools down and solidifies, radioactive "clocks"
it can be set. Geologists can use these "clocks" to
find out how long ago the rock formed.