1. Core Case Study Earth: The Just-Right, Adaptable Planet
During the 3.7 billion years since life arose, the average surface temperature of the earth has remained within the range of 10-20oC.
Figure 4-1

2. ORIGINS OF LIFE
1 billion years of chemical change to form the first cells, followed by about 3.7 billion years of biological change.
Figure 4-2

3. Biological Evolution
This has led to the variety of species we find on the earth today.
Figure 4-2

4. Origin Of Life Earth formed 4.6 billion years ago
When, and how did life originate?
Life is believed to have begun 3.5 billion years ago
How did the first life form come to exist?
Spontaneous generation theory accepted until 1862
Biogenesis paradox
If life comes from life how did the first life form evolve?

5. The First Organic Molecules
Miller and Urey produced amino acids, which are needed to make proteins, by passing sparks through a mixture of hydrogen, methane, ammonia, and water. This and other experiments suggested how simple compounds found on Early Earth could have combined to form the organic compounds needed for life!

6. Jewels of the Earth…click on picture

7. Earth’s Story

8. How Do We Know Which Organisms Lived in the Past?
Our knowledge about past life comes from fossils, chemical analysis, cores drilled out of buried ice, and DNA analysis.
Figure 4-4

9. Fossil Record Found in diverse environments: Sedimentary rock
petrified (stone) trees
molds left in stone
preserved organisms in amber
preserved bodies in areas with little decomposition (frozen in ice, in acid…)

10. Fossil Dating Relative Dating fossils are frozen in time
Compare similar strata of rock to obtain a relative date
Radiometric Dating (Absolute Dating) gives a more exact age for the fossil
Uses radioactive isotope half-lives

11. Geological Time Scales Four Eras: Precambrian Paleozoic Mesozoic
Cenozoic

12. 225 million years ago 225 million years ago 135 million years ago
Figure 4.5
Geological processes and biological evolution. Over millions of years the earth’s continents have moved very slowly on several gigantic tectonic plates. This process plays a role in the extinction of species as land areas split apart and promote the rise of new species when once isolated land areas combine. Rock and fossil evidence indicates that 200–250 million years ago all of the earth’s present-day continents were locked together in a supercontinent called Pangaea (top left). About 180 million years ago, Pangaea began splitting apart as the earth’s huge plates separated and eventually resulted in today’s locations of the continents (bottom right).
65 million years ago
Present
Fig. 4-5, p. 88

13. Continental Drift
Earth’s history explains geographical distribution of species
Continental drift has influenced major evolutionary events
250 mya all land masses converged into Pangaea
Drifting of continents helps explain:
marsupials of Australia
matching fossils in Brazil and West Africa

14. Major Adaptive Radiations
Evolve novel characteristic
Novel characteristic opens an adaptive zone
Animal evolution of hard body may have led to Cambrian explosion
Mammals with unique novelties did not diversify until dinosaurs opened up the adaptive zone to them

15. Extinction: Lights Out
Extinction occurs when the population cannot adapt to changing environmental conditions.
The golden toad of Costa Rica’s Monteverde cloud forest has become extinct because of changes in climate.
Figure 4-11

16. Species and families experiencing mass extinction
Bar width represents relative
number of living species
Millions of
years ago
Era
Period
Extinction
Current extinction crisis caused
by human activities. Many species
are expected to become extinct
within the next 50–100 years.
Quaternary
Today
Cenozoic
Tertiary
Extinction 65
Cretaceous: up to 80% of ruling
reptiles (dinosaurs); many marine
species including many
foraminiferans and mollusks.
Cretaceous
Mesozoic
Jurassic
Extinction
Triassic: 35% of animal families, including many reptiles and marine mollusks.
180
Triassic
Extinction
Permian: 90% of animal families, including over 95% of marine species; many trees, amphibians, most bryozoans and brachiopods, all trilobites.
250
Permian
Carboniferous
Extinction
345
Figure 4.12
Fossils and radioactive dating indicate that five major mass extinctions (indicated by arrows) have taken place over the past 500 million years. Mass extinctions leave many organism roles (niches) unoccupied and create new niches. Each mass extinction has been followed by periods of recovery (represented by the wedge shapes) called adaptive radiations. During these periods, which last 10 million years or longer, new species evolve to fill new or vacated niches. Many scientists say that we are now in the midst of a sixth mass extinction, caused primarily by human activities.
Devonian: 30% of animal families, including agnathan and placoderm fishes and many trilobites.
Devonian
Paleozoic
Silurian
Ordovician
Extinction
500
Ordovician: 50% of animal families, including many trilobites.
Cambrian
Fig. 4-12, p. 93

17. Major Extinctions Permian extinction - coincides with Pangaea
Cretaceous extinction - loss of dinosaurs
May have been caused by asteroid