The History of Life Chapter 17

1. The History of LifeChapter 17 Dr. Donna Howell Biology I Blacksburg High School

2. Part I: The Fossil Record

3. The Study of Fossils • Scientists who study fossils are called paleontologists. • The fossil record provides evidence about the history of life on Earth. • It also shows how different groups of organisms change over time.

4. The Study of Fossils • Fossils form when organisms die and some part of them are preserved. • Fossils layer upon each other, so the further down a fossil, the longer the amount of time that has passed.

5. The Study of Fossils • Shells, bones, and hard parts of an organism’s body are better preserved than the soft parts. • Scientists look at the age of fossils, and for similarities and differences between fossilized remains and current organisms.

6. The Study of Fossils • A fossil is dated by a scientist by relative dating; that is, comparing the age of different fossils to each other.

7. The Study of Fossils • Another way to date fossils is by radioactive dating. • This is where the age of a fossil is calculated by the amount of remaining radioactive isotopes it has.

8. Geologic Time Scale • This is a time scale created by scientists to represent evolutionary time. • Divided into eras and periods.

9. Part II: Earth’s Early History

10. Earth’s Early History • The Earth is approximately 4.6 billion years old • It’s early atmosphere probably contained hydrogen cyanide, carbon dioxide, carbon monoxide, nitrogen, hydrogen sulfide, and water.

11. Earth’s Early History • In the 1950’s, Miller & Urey conducted an experiment to simulate Earth’s early conditions in the lab. • They found that mixtures of organic compounds necessary for life could have arisen from compounds on primitive Earth.

12. Earth’s Early History • Gradually, the Earth’s atmosphere turned into an oxygen atmosphere. • The rise of O2 caused some life forms to become extinct, while others evolved to utilize the O2.

13. Earth’s Early Life • It is believed that prokaryotic cells (bacteria) arose about 3.5 billion years ago. • Gradually, eukaryotic cells began to arise. • It is believed that eukaryotic cells arose from one prokaryotic cell “eating” another, and a symbiosis formed.

14. Endosymbiotic Theory • Evidence: • Mitochondria and chloroplasts contain DNA like bacteria • Mitochondria and chloroplasts also have ribosomes, like bacteria • Like bacteria, the mitochondria and chloroplasts divide by binary fission.

15. Reproduction • Most prokaryotes reproduce asexually (binary fission). • Gradually, sexual reproduction arose • This caused the evolutionary process to speed up because of the mutations that happened.

16. Reproduction • A few hundred million years after sexual reproduction arose, cells went from being unicellular to multicellular. • This caused a great increase in the diversity of life.

17. Part III: Evolution of Multicellular Life

18. Precambrian Era • 90% of Earth’s history occurred during the Precambrian Era. • Photosynthesis evolved, which contributed to increasing levels of oxygen in the atmosphere. • Life existed only in the sea.

19. Paleozoic Era • Great diversity of marine life. • The “Cambrian Explosion” occurred, many new life forms were evolving at a rapid pace. • Most phyla of plants and animals evolved during this time.

20. Paleozoic Era • The first vertebrates appeared. • More land habitats began evolving. • At the end of the Paleozoic Era, there was a mass extinction, which killed off about 95% of the ocean life.

21. Mesozoic Era • During this era, dinosaurs were the dominant life forms. • The first flowering plants also appeared. • The first birds appeared. • At the end of this era, another mass extinction occurred, and over half of plant and animal life was wiped out.

22. Cenozoic Era • In this era, mammals evolved adaptations that allowed them to live in various environments. • Often called the Age of Mammals. • Earth’s climate cooled, causing a series of ice ages.

23. Part IV: Patterns of Evolution

24. Macroevolution • Large-scale evolutionary patterns and processes that occur over long periods of time. • Six types: extinction, adaptive radiation, convergent evolution, coevolution, punctuated equilibrium, and changes in developmental genes.

25. 1. Extinction • More than 99% of species that have ever lived are now extinct. • Mass extinctions are caused by weather changes, asteroids hitting Earth, volcanoes erupting, changing sea levels, shifting of continents.

26. 2. Adaptive Radiation • When a single species evolve through natural selection and other processes into different types of species that look different and live in different ways. • Ex: Darwin’s finches

27. 3. Convergent Evolution • The process by which unrelated organisms come to resemble one another due to similar environments. • Ex: dolphins and penguins

28. 4. Coevolution • The process by which two species evolve in response to changes in each other over time. • Ex: orchid and hawk moth

29. 5. Punctuated Equilibrium • Patterns of long, stable periods of evolution interrupted by brief periods of rapid change. • Ex: moth color

30. 6. Developmental Genes • Small changes in an organism’s genome can results in large body changes over time. • Ex: common fly

31. The End!