17-2 EARTH’S EARLY HISTORY

I. FORMATION OF THE EARTH

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.

9. 4 bya the Earth cooled & solid rocks formed

10. Millions of years of volacanic activity shook the Earth’s crust

11. 3.8 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.

DISCUSS W/ PARTNER: 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. THE 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.

DISCUSS W/ PARTNER:

Pg. 424 Figure 17-81. 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?

ANSWERS: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. THE 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 cells4. 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 replicateb) Process mRNAc) Catalyze chemical

reactionsd) Grow & duplicate

themselves

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RNA & THE ORIGIN OF LIFE

RNA and the Origin of Life

Abiotic “stew” ofinorganic matter

Simple organicmolecules

RNA nucleotides

RNA able to replicate itself, synthesize proteins, andfunction in information storage

DNA functions in information storage and retrieval

RNA helps inprotein synthesis

Proteins build cellstructures and catalyzechemical reactions

IV. FREE OXYGEN

1. 3.5 bya photosynthetic bacteria was common in the oceans

a) These bacteria absorbed CO2 & released O2

2. 2.2 bya the O2 released from the bacteria started to build up in the atmosphere

3. Increased O2 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. TheseRocklike formations are called stromatolites, were made by cyanobacteria, which were Probably among the earliest organisms to Evolve on earth

V. ORIGIN 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

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Endosymbiotic Theory

Mitochondrion

Aerobicbacteria

Nuclear envelopeevolving

Ancient Prokaryotes

Plants and

plantlike protists

Primitive PhotosyntheticEukaryote

Primitive AerobicEukaryote

Ancient AnaerobicProkaryote

Chloroplast

Animals, fungi, and

non-plantlike protists

Photosynthetic bacteria

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ORIGIN OF EUKARYOTIC CELLS

Ancient Anaerobic Prokaryote

Nuclear envelopeevolving

Aerobicbacteria

Ancient Prokaryotes

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ORIGIN OF EUKARYOTIC CELLS Prokaryotes that use oxygen to generate energy-rich molecules of ATP evolved into mitochondria.

Mitochondrion

Primitive Aerobic Eukaryote

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ORIGIN OF EUKARYOTIC CELLS

Primitive Photosynthetic Eukaryote

Chloroplast

Photosynthetic bacteria

Prokaryotes that carried out photosynthesis evolved into chloroplasts.

VI. SEXUAL REPRODUCTION & MULTICELLULARITY

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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.

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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