LLL Innis 3 2018

A BRIEF HISTORY OF LIFE ON

EARTH

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.

Species numbers of plants

Species richness of

primates, bats and birds.

Global

photosynthesis.

phytoplankton

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.

Let’s do a quick history of life on Earth

Changes in our atmosphere

through time.

Early lifeforms were extremophiles

living in marginal environments.

Hydrothermal vents (deep smokers); probably

the sites for the earliest life on Earth.

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?

Pattern of life for the last 600,000 years.

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).

Ediacaran fauna, 600-545 MYBP

The latest Burgess Shale fossil –

Kootenayscolex barbarensis, a bristle worm.

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 Big Five

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 animals V= birds, BB= placental mammals

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.

Some eastern Canadian

craters.

Sudbury crater. 62km

long, 30km wide. 1.8

billion years old.

Asteroid or comet?

Chicxulub crater, Yucatan, 180 km

diameter, 20 km deep, age 65 MY.

Physical signature of

impact – iridium, tektites

and shocked quartz.

Biological signature

The Sixth Extinction

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