17-2 E ARTH ’ S E ARLY H ISTORY

I. F ORMATION OF THE E ARTH

1. Based on geologic evidence Earth was formed 4.6 billon years ago (bya) 2. Pieces of debris were attracted to each other based on their chemical bonding over 100 million years.

3. A large object hit the earth, resulting in the production of so much heat that the earth melted. 4. The elements on the now melted earth rearranged themselves according to density.

5. The most dense elements are in the middle, forming Earth’s core. 6. The less dense elements formed the top forming earth’s surface. 7. The surface cooled and formed a solid crust

8. The early atmosphere contained hydrogen cyanide, carbon dioxide, carbon monoxide, hydrogen sulfide (all poisonous gases), nitrogen & water bya the Earth cooled & solid rocks formed 10. Millions of years of volacanic activity shook the Earth’s crust

bya the Earth cooled enough to allow liquid water to form which formed the oceans 12. The oceans were brown due to high amounts of iron in the water.

D ISCUSS W / P ARTNER : 1. What features can you see on Earth’s surface in the photograph and in the drawing? 2. What are the basic requirements for human life that re found on Earth today? 3. Which basic requirements were present on early Earth?

II. T HE FIRST ORGANIC MOLECULES

1. In the 1950s, Stanley Miller and Harold Urey wanted to find out if organic molecules could have evolved under conditions on early Earth 2. Amino acids were produced from inorganic compounds in the apparatus 3. Their experiment suggest how life could have arisen from a few chemicals in the ocean.

D ISCUSS W / P ARTNER : Pg. 424 Figure Why did Miller & Urey use a mixture nitrogen, hydrogen, methane, and ammonia in their apparatus? 2. Why did they boil water to produce water vapor? 3. What was the purpose of the electric sparks? 4. Does the Miller-Urey experiment show what actually happened on early Earth?

A NSWERS : 1. Why did Miller & Urey use a mixture nitrogen, hydrogen, methane, and ammonia in their apparatus? B/c this mixture of gases resembles Earth’s early atmospheres. 2. Why did they boil water to produce water vapor? To prevent oxygen from entering, b/c Earth’s early atmosphere had no oxygen, & to prevent contamination by modern bacteria or fungi. 3. What was the purpose of the electric sparks? To simulate lightning & provide energy for the chemical reactions. 4. Does the Miller-Urey experiment show what actually happened on early Earth? No, it is only a model showing how organic molecules could have been produced from inorganic components.

III. T HE PUZZLE OF LIFE ’ S ORIGINS

1. Proteinoid Microspheres- tiny bubbles of organic molecules 2. Hypothesis suggest that structures like p.m. become more & more like living organisms. 3. Are NOT cells 4. Like cells proteinoid microspheres: a) selectively permeable membranes b) can store and release energy Proteinoid microspheres magnification about 10,000x)

5. Scientist are not sure how RNA and DNA evolved. 6. Scientist think RNA evolved before DNA because some RNA sequences can: a) Help DNA replicate b) Process mRNA c) Catalyze chemical reactions d) Grow & duplicate themselves

RNA & THE O RIGIN OF L IFE RNA and the Origin of Life Copyright Pearson Prentice Hall Abiotic “stew” of inorganic matter Simple organic molecules RNA nucleotides RNA able to replicate itself, synthesize proteins, and function in information storage DNA functions in information storage and retrieval RNA helps in protein synthesis Proteins build cell structures and catalyze chemical reactions

IV. F REE O XYGEN

bya photosynthetic bacteria was common in the oceans a) These bacteria absorbed CO 2 & released O bya the O 2 released from the bacteria started to build up in the atmosphere 3. Increased O 2 levels caused a mass extinction of some species but generated the evolution of many other species. Ancient photosynthetic organisms produced a rise in oxygen in Earth’s atmosphere. These Rocklike formations are called stromatolites, were made by cyanobacteria, which were Probably among the earliest organisms to Evolve on earth

V. O RIGIN OF EUKARYOTIC CELLS

1. The endosymbiotic theory explores how eukaryotic cells evoled from prokarytotic cells 2. Endosymbiotic Theory- eukarytoic cells formed from living together with prokaryotic organisms

Endosymbiotic Theory Copyright Pearson Prentice Hall Mitochondrion Aerobic bacteria Nuclear envelope evolving Ancient Prokaryotes Plants and plantlike protists Primitive Photosynthetic Eukaryote Primitive Aerobic Eukaryote Ancient Anaerobic Prokaryote Chloroplast Animals, fungi, and non- plantlike protists Photosynthetic bacteria

O RIGIN OF E UKARYOTIC C ELLS Copyright Pearson Prentice Hall Ancient Anaerobic Prokaryote Nuclear envelope evolving Aerobic bacteria Ancient Prokaryotes

O RIGIN OF E UKARYOTIC C ELLS Prokaryotes that use oxygen to generate energy-rich molecules of ATP evolved into mitochondria. Copyright Pearson Prentice Hall Mitochondrion Primitive Aerobic Eukaryote

O RIGIN OF E UKARYOTIC C ELLS Copyright Pearson Prentice Hall Primitive Photosynthetic Eukaryote Chloroplast Photosynthetic bacteria Prokaryotes that carried out photosynthesis evolved into chloroplasts.

VI. S EXUAL R EPRODUCTION & M ULTICELLULARITY

Copyright Pearson Prentice Hall 1. Most prokaryotes reproduce asexually. Asexual reproduction: a) Results in daughter cells that are exact copies of the parent cell. b) restricts genetic variation to mutations in DNA.

Copyright Pearson Prentice Hall 2. Sexual reproduction shuffles genes in each generation. 3. In sexual reproduction: a) offspring never resemble parents exactly b) there is an increased probability that favorable combinations will be produced c) there is an increased chance of evolutionary change due to natural selection