1. Chapter 12 – History of Life on Earth High School Biology Class

2. I. When did the Earth begin? The Earth formed about 4.5 billion years ago according to evidence obtained through radiometric dating. Radiometric dating is a process used to calculate the age of an object by measuring the amount of radioactive isotopes inside that object.

3. Quick Chemistry Review Matter is anything with mass and volume. The smallest unit of matter is an atom. Atoms are made of protons, neutrons, & electrons. The type of atom is determined by the number of protons (atomic number) it contains.

4. Quick Chemistry Review Sometimes similar atoms have different masses. For instance: Carbon, which always has 6 protons, usually has 6 neutrons as well. However, carbon may occasionally have 7 or even 8 neutrons, which give the atom more mass.

5. Quick Chemistry Review Atoms that have different masses are isotopes. Isotopes that are unstable breakdown to become stable atoms when given enough time.

6. Important Terms: Radioisotope – an unstable atom that breaks down and gives off energy in the form of radiation. An important characteristic of all radioisotopes is that the amount of time it takes to breakdown is always the same.

7. Important Terms: Half-life – the time it takes for ½ of a given amount of radioisotopes to breakdown.

8. Carbon Dating Process 1.Radiometric dating confirms the age of an object. 2.Carbon-14 is a radioactive isotope. 3.Living things obtain carbon from carbon dioxide in the air. (Some of the carbon they take in is Carbon-14.) 3.When a living thing dies, the Carbon-14 begins to decay, and after 5730 years ½ of it will be gone. 4.Once we find a fossil its age can be determined by measuring the amount of Carbon-14 in it.

9. Carbon Dating Table Half-lives Years past C-14 Atoms Example 0123456701234567 0 5,730 11,460 17,190 22,920 28,650 34,380 40,110 1 1/2 1/4 1/8 1/16 1/32 1/64 1/128 1000 500 250 125 62.5 31.25 15.625 7.8125

10. II. How did Life begin? Most scientists think that life on Earth developed through natural processes (spontaneous origin). i) Atoms that became energized, from the sun or volcanoes, reacted to form simple molecules. ii)Gradually these reacted to form more complex organic molecules. iii)Eventually they formed the first cell.

11. A) Molecules Formed Cells Cech & Altman (1980) showed RNA could be formed in water. (RNA contains Heredity Information) Simple observations show that lipids group together in water like oil in water. (Membranes) Further examination shows that amino acids group together into microspheres. (Proteins)

12. A) Molecules Formed Cells All of these observations provide the framework from which the first cell could have arisen. However, the formal process as to how all of the pieces came together is of intense interest and research among scientists currently.

13. III. Complex Organisms Developed To find out when the first organisms formed, scientists study fossils. Fossil – preserved or mineralized remain or imprint of an organism that lived long ago.

14. How Are Fossils Helpful? They provide us with a Geological Time Scale (a record in the rocks.) The lowest layers are usually the oldest fossils.

15. The Oldest Fossils? Prokaryotes are single celled organisms that lack a nucleus they are often called bacteria. The earliest forms of life were simple prokaryotic cells. They were basically just collections of synthesized biomolecules. They had no advanced cell functions

16. Do Most Organisms Leave Fossils? NO! But why not? Absence of fossilizing environment. Lack of hard tissues or parts capable of fossilizing. Body scavenged/decomposed before fossilization. Nature destroyed the fossil after formation. The fossil has not yet been discovered.

17. Other Bacteria? Bacteria can be divided into two types: 1) Eubacteria contain the chemical peptidoglycan in their cell walls. (Usually cause diseases.) 2)Archeabacteria do NOT contain peptidoglycan. (Related to first bacteria)

18. Prokaryotes to Eukaryotes Prokaryotes gave rise to eukaryotes through the process of endosymbiosis. Mitochondria once were free living bacteria. The mitochondria formed a partnership with other bacteria species. In exchange for protection, the mitochondria provided the host bacteria with energy. This partnership is called…? Thus from prokaryotes came eukaryotes.

19. Prokaryotes to Eukaryotes

20. Eukaryotes to Multicellularity Eukaryotes then branched into four new kingdoms of more complex organisms: 1) Protists 2) Fungi 3) Plants 4) Animals Cambrian Explosion [540 mya to 505mya]

21. Do All Organisms Survive? NO! There have been 5 major mass extinctions that have occurred on the Earth. Mass extinctions are usually caused by a large ecological disaster. Species also go extinct regularly through normal ecological processes.

22. Early Life The first cells appeared 3.6 billion years ago. The first photosynthetic bacteria (cyanobacteria) arose ~3 billion years ago. These bacteria began creating the ozone layer. Endosymbiosis created the first eukaryotes ~2 billion years ago. Multicellular organisms arose ~1 billion years ago. Early animals arose 600 million years ago.

23. Early Life was Water-Based Most materials for life could only be found in water. (nutrients, water, etc.) When the Earth first was formed life did not exist on land due to strong UV radiation. Once cyanobacteria appeared (3 bya) and began creating oxygen an ozone barrier was established to protect against the radiation.

24. The Ozone Shield Oxygen (O 2 ) molecules get split and reformed as ozone (O 3 ) molecules. UV radiation then gets blocked out by O 3.

25. Arthropods Crawl Out Of Sea Plants and fungi created habitats that could support (feed, protect) other organisms. The first animals to successfully invade the land from the sea were arthropods 530 mya (lobsters, crabs, insects, spiders, scorpions, etc.) The insects have become the most plentiful and diverse group of animals in the history of the Earth.

26. Fish Evolve In The Sea The first vertebrates (animals with backbones) were jawless fish. 485 mya The jaw formation helped fish bite and chew instead of suction up their food. Fish became the most abundant animals in the history of the Earth making up about ½ of all vertebrates.

27. Plants & Fungi Take Over The Land Plants can do photosynthesis but cannot get minerals from bare rock. Fungi can harvest minerals but cannot photosynthesize. The two form a mutual partnership called a mycorrhizae. 430 mya

28. Amphibians Move Out Of Sea The first vertebrates to inhabit the land were amphibians. 340 mya They were able to live in live on land because they had smooth skin and lungs, but their eggs needed water.

29. Amphibians Lead To Reptiles Reptiles were new species of animals that arose from amphibians. 305 mya Reptiles had watertight skin and eggs that could survive on dry land.

30. Reptiles Take Flight, Grow Hair Mammals also emerged from reptiles and were able to reproduce without laying eggs. 225 mya Birds emerged from the reptiles and were able to populate new habitats. 95 mya

31. Mammals Take Charge When the dinosaur (large reptile) extinction occurred 65mya it opened new chances for the mammals to emerge as the dominant life form on land.