Changing Evolution
Mass extinction of life has occurred several times in world
history. The most famous one was the disappearance of the dinosaurs
65 million years ago. The prevailing theory to explain the
termination of these creatures is the collision of an asteroid or
comet 10 kilometres in diameter with our planet. Travelling with
the speed of at least 11 kilometres per second the impact created a
crater 30 kilometres deep and 100 kilometres in diameter. Within
minutes molten rock was raining down all over the globe, setting
forests afire. Ashes in the atmosphere then prevented the sunlight
to get through, causing a deep frozen climate for months. This
series of events killed not only the dinosaurs but almost any
developed life forms.
450 Million years ago (on a sunny Friday afternoon)
The Brent Crater is actually way older than the impact site in
Mexico. 450 million years ago a rock with only 150 metres in
diameter , travelling at 11-20 kilometres per second, hit the
Canadian shield just where you stand now. What followed equals pure
devastation: A hole 4 kilometres wide, 600 metres deep and with the
rim raised up 100 metres above the pre impact level. A force
similar to 250 million tons of TNT that triggered an earth quake
stronger than anything human kind has experienced so far. Buildings
would have collapsed even in places like Ottawa more than 225
kilometres away and no tree remained standing for 60 kilometres in
any direction around the impact site (now this somewhat still
applies today but is related to the foresting happening at some
spots in Algonquin).
Resistant to Erosion
4 ice ages and a long time of erosion have changed the impact site
compared to how it looked like back then. However – and that
makes this place so precious for scientists – the bedrock
formations of the Canadian Shield showed strong resilience against
the influence of wind and weather. This is the reason why we can
still see the shape and rim of the original crater. Sure –
the crater’s rim has sloped and the bottom has filled with
rocks and lakes over time, but you can still see and feel the
magnitude of what happened here.
What you need to do to log this earth cache:
a. Go to the Sign at the given coordinates and report the thickness
of the layer of sedimentary rocks that have accumulated at the
bottom of the Crater in the given unit of measurement (aren’t
we metric, eh?)
b. Climb up the Tower. Now you take a picture of the crater and a
body part of you (I believe in privacy and confidentiality - so you
can pick if you want to show us your back, your face, your foot,
your bottom, your knee or anything) . Yes – I need to see
your GPS. AND you need to smile even if your face is not on the
picture (Algonquin is a fun place) or make a funny face. Grumpy
pics don’t qualify (unless funny to look at). I acknowledge
that it might take some special athletic skills to capture your
bottom, your GPS and the crater on one photo. :-) Please post
picture.
c. This earth cache is #3 of a series of earth caches that
highlight the beauty and geological history of Algonquin Park.
Please add a picture of a landscape, an animal, a campfire setting,
a pile of moose loose or anything else that you think contributes
to the special flair of Algonquin. And yes, a picture of the guys
running the unique Brent Store is a GREAT IDEA.
d. You really want to overachieve? Here are some special
voluntary tasks:
1. Bronze achievement: Are the lakes within the crater sensitive to
acid? Why or Why not? (and do fish really care?)
2. Silver achievement: Walk the trail. Check the elevation at Post
#4. The original rim of the crater was approx. 250 metres higher
than the elevation at #4. Please send approx. elevation of the
original rim.
3. Gold achievement: The Brent Crater was formed by the combination
of speed and volume of the meteorite. Let’s assume the
meteorite with a diameter of 150m (r=75m) was a perfectly ball
shaped object. As you learned it created a crater 600m deep and
4000m wide.
Volume of a ball = 4/3 * pi * r * r * r
Now calculate how deep and wide the crater would be if the
meteorite had a diameter of just 100m (r=50m). Assume that depth
and width of the crater are changing proportional to the meteorites
volume.
I really recommend you take the 90 minutes to walk the trail. Get a
brochure at the start of the trail (100 metres past the Observation
Tower) and please make sure you pay the marginal fee.