Back in the 1980s
observations of a layer of sediment right when the dinosaurs went
extinct led to a hypothesis of an asteroid or comet impact being the
cause of the extinction. Like many hypotheses that are fairly
radical, it took a while to gain acceptance, yet now it is considered
the likely cause of the extinction.
There is a saying
that when your only tool is a hammer everything starts to look like a
nail. And this is true of scientists too. So after the dinosaur
extinction was determined to have been caused by an impact from
space, other scientists started to look at other extinctions and
hypothesized they took were caused by some kind of impact from space.
For example, during
the last Ice Age, here in North America, there was an extinction of
most of the largest animals. Mammoths, horses, and saber-tooth cats
are all examples of the mammals that went extinct towards the end of
the last Ice Age. So some scientists started looking for evidence
that there was some kind of impact that caused it, actually
hypothesizing that there was an impact in the air above the ice sheet
that was covering the area that became the Great Lakes.
So to check their
hypothesis they started to look for evidence and found things that
were consistent with an impact. Certain residues in soot found around
the world at the time, for example. And nano-diamonds for another. So
there has been some evidence that is consistent with the theory.
Which generates more interest and then more research.
But when you do the
research, sometimes you find things that are not consistent with the
theory. For example, since the hypothesized impact had to affect
climate around the world we should be able to look for evidence all
over the world. Well one research project in Syria looked at
particles formed by fire found at about the right depth. However, the
results didn't indicate that the particles were formed by an impact.
This was because
the particles were formed from the local soil, not soil from around
the world in North America. The particles were formed at much lower
temperatures that an impact would generate, and they were formed over
a period of time and not a single time like an impact.
But what caused
this soot and the particles? Well, these scientists looked at time
they would have been formed 10,000-13000 years ago and realized that
people in that region were starting to live in villages, agriculture
was getting started at that time, and the formation of the soot they
looked at was consistent with their mud and straw houses burning
down.
So while some
evidence has been found to support an impact towards the end of the
last Ice Age, here's a strike against the hypothesis. So scientists
will continue to investigate the cause of the extinction around
13,000 years ago. It has been a big question for many years, and they can pull
other tools from their toolbox to determine what happened.
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