Welcome to the fray lasthero, lurk no more.
A recent topic on the subject of impact craters on the Moon got me thinking about the impact craters on Earth. On another forum, I posed this question to the creationists in attendance
Well done.
Another piece of information to bring up:
NASA -
Evidence Of Meteor Impact Found Off Australian Coast
quote:
An impact crater believed to be associated with the "Great Dying," the largest extinction event in the history of life on Earth, appears to be buried off the coast of Australia.
Becker and her team found extensive evidence of a 125-mile-wide crater, called Bedout, off the northwestern coast of Australia. They found clues matched up with the Great Dying, the period known as the end-Permian. This was the time period when the Earth was configured as one primary land mass called Pangea and a super ocean called Panthalassa.
and then we have:
Are Radioactive Dating Methods Consistent?
quote:
To check, we need one single event which has been dated by several methods. A nice example is the Triassic multiple-impact event, which formed a 4500-kilometer-long chain of huge craters. (There must have been a train of big objects from space, which hit the spinning earth, one by one, across several hours. Much like the way comet Shoemaker-Levy hit Jupiter in 1994.)
Here are the five confirmed craters:
| Crater | Country | Diameter | Million Years Ago | Dating Method
|
| Manicouagan | Canada | 100 km | 214 1 | U-Pb on zircons
|
| Saint Martin | Canada | 40 km | 219 32 | Rb/Sr
|
| Rochechouart | France | 25 km | 214 8 | Ar/Ar laser spot fusion
|
| Obolon | Ukraine | 15 km | 215 25 | stratigraphic
|
| Red Wing | USA | 9 km | 200 25 | stratigraphic
|
"Stratigraphic" dating means that the crater itself has not been dated. Instead, the rock strata above and below the crater was dated. (By now, the Red Wing crater is under 1.5 kilometers of sediment.)
The table shows five datings that are consistent with each other. However, there is a sixth dating involved: the one for drawing the map.
Today, the continents are moving about one inch a year. This is a simple fact which can be measured by anyone with good GPS equipment. So, in 214 million years, the continents could have moved three thousand miles. To get a map of that past world, geologists did K/Ar datings of ancient lava flows. As the article below shows, the three main craters form a dead straight line on that map.
These dates were obtained by several different radioactive methods, on rocks of several different kinds, by geologists from four different countries. But the dates are consistent. That is the usual case, so the article didn't bother to comment on it.
For more detail:
Evidence for a late Triassic multiple impact event on Earth, J. Spray, S. Kelley, and D. Rowley, Nature 392,171-173 (12 March 1998)
Paleographic Atlas Project: Pictures related to the Multi-Impact Event
High correlations of dates by several different methods.
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