LLL Innis A BRIEF HISTORY OF LIFE ON EARTH

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Matilda Dalton
5 years ago
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1 LLL Innis A BRIEF HISTORY OF LIFE ON EARTH

2 A few loose ends from last week; ,The Year Without Summer. See article in Canada s History, Aug-Sept It can be accessed from; niche-canada.org/yearwithoutsummer/

2.Numbers of earthquakes; <2.5 900,000/year 2.5-5.

3 2.Numbers of earthquakes; < ,000/year ,000/year /year /year /year > 8 1 every 1-10/years

4 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!).

5 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.

6 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.

7 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.

8 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.

9 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.

10 Species numbers of plants

11 Species richness of primates, bats and birds.

12 Global photosynthesis. phytoplankton

13 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.

15 Let s do a quick history of life on Earth

16 Changes in our atmosphere through time.

17 Early lifeforms were extremophiles living in marginal environments.

19 Hydrothermal vents (deep smokers); probably the sites for the earliest life on Earth.

20 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 welladapted species. What caused these traumas and what impact did they have on evolution?

21 Pattern of life for the last 600,000 years.

23 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 softbodied animals. In Canada, they are called the Burgess Shale fauna (from the site in Yoho National Park).

24 Ediacaran fauna, MYBP

25 The latest Burgess Shale fossil Kootenayscolex barbarensis, a bristle worm.

26 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?

27 The Big Five

28 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.

29 Evolution of animals V= birds, BB= placental mammals

30 Evolution of plants and animals after the K-T event. angiosperms=flowering plants, ungulates=hoofed animals, macropods= marsupials.

31 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.

33 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.

35 Some eastern Canadian craters.

36 Sudbury crater. 62km long, 30km wide. 1.8 billion years old. Asteroid or comet?

37 Chicxulub crater, Yucatan, 180 km diameter, 20 km deep, age 65 MY.

38 Physical signature of impact iridium, tektites and shocked quartz.

39 Biological signature

40 The Sixth Extinction

41 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!

42 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.

43 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.

44 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

The Phanerozoic Eon. 542 mya Present. Divided into 3 Eras The Paleozoic, Mesozoic, and Cenozoic Eras

The Phanerozoic Eon. 542 mya Present. Divided into 3 Eras The Paleozoic, Mesozoic, and Cenozoic Eras 542 mya Present The Phanerozoic Eon Divided into 3 Eras The Paleozoic, Mesozoic, and Cenozoic Eras The ends of the Paleozoic and Mesozoic Eras were marked by mass extinctions The Cenozoic Era is still