A few loose ends from last week;
1. 1816,The Year Without Summer. See
article in Canada’s History, Aug-Sept.
2016. It can be accessed from;
niche-canada.org/yearwithoutsummer/
2.Numbers of earthquakes;
<2.5 900,000/year
2.5 - 5.4 30,000/year
5.5 – 6 500/year
6 – 6.9 100/year
7 - 7.9 20/year
> 8 1 every 1-10/years
Let’s look at life on Earth; its origins, its
evolution and the role that climate has
played in it all.
A number of features stand out;
1. life has been around almost as long as
the Earth has existed.
2. that life was largely microbial for about
2 billion years (half of our history!).
3. microbial life gave way to more
complex lifeforms, particularly from
the Cambrian, about 550,000 years
ago (the Cambrian Explosion).
4. although there appears to be an
increase in species numbers
through time, that increase has not
been smooth.
5. the record shows a series of major traumas (mass extinctions) that may have eliminated as much as 90% of species.
6. every mass extinction event was also a time of opportunity (speciation).
7. the Big Five extinctions are generally recognized, but there were others.
8. the modern biosphere stems from the last of these major events (at the Cretaceous-Tertiary boundary, 65 million years ago).
We are currently in a Sixth Extinction and we are responsible for it.
The current relationship between life
and climate;
We can think of life as a product of the
Goldilocks effect, but it’s also a major factor in
causing and maintaining the condition.
For example, the levels of oxygen and carbon
dioxide in our atmosphere are related to
photosynthesis, a process that’s been
around nearly 3 billion years.
Photosynthesis requires light and water,
but is also temperature dependent. This
is reflected in the global pattern of
species richness. There is a strong
equator to pole pattern in terrestrial
species richness, but that pattern is not
repeated in the oceans.
How many species are there?
We don’t know. Estimates range from
several million to billions.
What’s the problem? Big things are
easy to count, but little things aren’t.
Whatever the number, we have
described only a few percent of what is
here.
Mass extinctions and speciation.
The pattern of increasing species richness is
interrupted by a series of extinction events
that seem to be biologically devastating.
The Big Five mass extinction events
eliminated up to 90% of apparently well-
adapted species.
What caused these traumas and what
impact did they have on evolution?
Although we focus on the Big Five, there have been other events.
One of those occurred about 550 MY ago, in the Cambrian.
It’s marked by the demise of the Ediacaran fauna, a strange set of soft-bodied animals. In Canada, they are called the Burgess Shale fauna (from the site in Yoho National Park).
The Cambrian Explosion refers to the rapid
emergence of complex lifeforms and the demise
of the earlier simple, soft-bodied forms at around
540 MY ago. Cause?
Global glaciation?
Asteroid impact?
Both?
The Cretaceous-Tertiary (K-T) event.
Not the biggest, but for us the most important one. The extinction at the K-T boundary started the modernization of our biota. From K-T we see an increase in the numbers and variety of mammals, birds, insects and flowering plants. The primates evolve from this time.
Evolution of plants and animals after the K-T event .
angiosperms=flowering plants, ungulates=hoofed
animals, macropods= marsupials.
It’s the mass extinction that draws
most attention in part because it
brought the demise of the
dinosaurs, but also because we can
make a good case for asteroid
impact as the cause.
To establish asteroid impact as cause we need to demonstrate that;
impacts of appropriate size occur
there is coincidence of the event with the mass extinction
the physical and chemical signatures of impact are in evidence
the biological responses fit the scenario.
One of the inevitable conclusions to this look
at the history of life is that the Darwinian
concept of survival of the fittest is only one
of a number of forces in play.
Another is that evolution is not directional.
We are not the end product of 4 billion years
of evolution. We are here by accident. Not
good for our collective conceit!
The modern biosphere dates from the K-T
boundary. The new biosphere becomes
dominated by mammals and
angiosperms.
These evolve in a world that gets
progressively cooler and culminates in
the accumulation of continental ice, a
contraction of tropical forests and the
expansion of grasslands and deserts.
Primates emerge in this changing
world. By 7 MY ago, hominids
evolve from the great apes. Next
week we’ll look at why, how, where
and when.
My song list; Barry McGuire Eve of Destruction
Bill Withers Ain’t No Sunshine
Bing Crosby Heat Wave
Elvis Presley Early Morning Rain
Etta James Stormy Weather
Flanders and Swann A Song of The Weather
Jimmy Cliff Save Our Planet Earth
Katrina and the Waves Walking on Sunshine
Lord Christo Hurricane Janet
Marvin Gaye Mercy Mercy Me
Neil Young/Crazy Horse Mother Earth Natural Anthem
Paddy Reilly The Fields of Athenry
The Beatles Here Comes The Sun
The Corrie Hush Hush
The Doors Riders of The Storm
Willie Nelson Fire And Rain