GeologyRocks

I just watched that!

It was ok, but to be honest, I'm not convinced either way, both theories have flaws so they need to come up with a better explanation.

~Jenny~

Jon and I will be watching that tonight (we taped it). I'll post back to let you know what I think later...

Finally got around to watching it.

For those that did not see it, here is a breif synopsis:

The original impact theory implicated the Chicxulub crater as the bringer of death at the K-T boundary. Evidence included an iridium spike, imapct spherules, a crater, a fern "spike" and a large sand body between spherules and the iridium which was interpreted as a tsunami. The general scenario is the meteor hit, tsunamis occured, fires, flame etc. Then a dust cloud caused an "atomic" winter killing off things (but not everything!).

There are several problems with this:
o Not obvious why the creatures that went extinction died and other did not. Why did frogs, crocs sharks and mammals survive, but dinos, ammonites and whole heap of forms did not?
o If there was widespread fires (indicated by soot levels) where is the charcoal? The whole of N. America has been searched, but there is very little. But the fern "spike" indicates that most plants died at this time.
o The "tsunami" sand deposit has bioturbation in it - that need seperate events and months, even years between these events.
o There are limestones and mud horizons in between these sand bodies on some localities, which invalidates the tsunami, unless these are remobalised sediments.
o Dinos and ammonites were becoming extinct anyway. Numbers had declined a lot in the 10 Myr preceeding the K-T boundary. Of course this is from the fossil record - not the best indicator of species number!
o Possible glauconite in the limestone - this takes 100's of years to form

Some of these can be dissmissed - the glauconite could be smectite (how they've mis-interpreted this, I don't know!). The mud and limestone can be redeposited stuff - you would imagine a tsunami would mix things up a bit. However a few things can't be dismissed - the main one is the bioturbation. Unfortunately the programme did not explain why the proponents of the Chicxulub crater could dismiss this evidence.

I've gathered a few links so far. I'll look for more later.

http://www.geolsoc.org.uk/template.cfm?name=NSG2349857238495
http://www.geo.vu.nl/~smit/csdp/chicxulub.pdf
http://www.geo.vu.nl/~smit/ktboundary/K_Tboundary.html
http://www.geo.vu.nl/~smit/csdp/debates.htm

In these pages Smit does account for the bioturbation - by dismissing it as one burrow in 40 sections. Still one burrow is one burrow. I think it's best I go out there and do some field work

Jon

A short news story in New Scientist (16th October, 2004) has thrown up some more questions on this subject. According to David Fastovsky at University of Rhode Island, Dinos were increasing in numbers up to the K-T boundary. The number of genera increased from around 25 in the Late Triassic/Early Jurassic to 150 in the Early Cretaceous and nearly 250 in the Late Cretaceous. This is at complete odds to one of the scientists that were interviewed in the BBC programme, who clearly said that Dinos were dying out. However, his evidence was based on ammonite and other fossil numbers (if I remember correctly). This makes the asteroid (or whatever it was!) the sole killer of dinos.

Jon

Looks like there's some more questions to be answered before this debate is settled!

http://news.bbc.co.uk/1/hi/sci/tech/4030933.stm

It appears that tropical honeybees survived the "post-impact winter" caused by the asteroid/meteorite.

Modern tropical honeybees have an optimal temperature range of 31-34C, but current theories about the Chicxulub impact winter estimate drops of 7-12C which which makes it too cold for tropical honeybees to survive.

~Jenny~

Interesting stuff...However, just because a bee looks the same as a bee does today, it doesn't mean they acted like they do too. The bees found may have had a lower temperature requirement of they may be able to hibernate - who knows!

However, everything may still work out...the lower limit of the bee survival temperature (7 deg C) is the same as the smallest temperature drop that could have occurred due to the Chicxulub crater...there is some overlap.

Jon