| A | B |
|---|
| How old is Earth? | It's 4.6 billion years old. |
| What is the theory about Earth's early history? | Cosmic debris collected; it was hit by a large object (maybe Mars); Earth melted; elements rearranged themselves according to density; the core is most dense; moderately dense elements went to the surface, cooled and formed a solid crust; least dense formed atmosphere. (See 424 for more) |
| Wht elements did early Earth's atmosphere contain? | Hydrogen cyanide, carbon dioxide, carbon monoxide, nitrogen, hydrogen sulfide, water. (Humans would not have survived.) |
| Why was there no water on early Earth? | The Earth's surface was too hot. |
| Explain why atoms do not assemble themselves into complex organic molecules or living cells on Earth today. | 1) Oxygen in the atmosphere is very reactive & would destroy many kinds of organic molecules not protected within cells; 2) as soon as organic molecules appeared, bacteria or some other life form would probably eat them. |
| What was the importance of Miller and Urey's experiments? | They suggested how mixtures of the organic compounds necessary for life could have arisen from simpler compounds present on a primitive Earth. (See 424) |
| What are proteinoid microspheres? | They're tiny bubbles, formed of large organic molecules, that have some characteristics of a cell. |
| What characteristics of cells do proteinoid microspheres have? | They have selectively permeable membranes through which water molecules can pass; they can store and release energy. |
| What evidence is there that RNA existed before DNA? | Some RNA molecules can grow and duplicate themselves; see the diagram on pg. 425. |
| What do we call the first life forms on Earth, and what was unique about those life forms? | 1) They're called microfossils of single-celled prokaryotic organisms. 2) They had to evolve without oxygen, as there was little of that gas then. |
| What function did the photosynthetic bacteria in the shallow seas of the Precambrian serve? | They steadily made oxygen (one end product of photosynthesis). See 426 to see what happened to that oxygen. |
| From where did the oxygen in the atmosphere come? | It came from photosynthesis in the oceans, accumulating in the atmosphere. |
| As oxygen increased in the atmosphere, what happened? | Some life forms became extinct; other life forms then evolved. Organisms that had evolved in an oxygen-free environment had to find anaerobic habitats. |
| What does the endosymbiotic theory maintain? | It proposes that eukaryotic cells arose from living communities formed by prokaryotic organisms. (see diagram pg. 427) |
| What evidence is there that free-living bacteria and the organelles of living eukaryotic cells have a common ancestry? | 1) Mitochondria & chloroplasts contain DNA similar to bacterial DNA; 2) Mitochondria & chloroplasts have ribosomes whose size & structure closely resemble those of bacteria; 3) like bacteria, mitochondria & chloroplasts reproduce by binary fission when the cells containing them divide by mitosis. |
| What development in eukaryotic cells allowed the rate of evolution to speed up considerably? | Eukaryotic cells started to reproduce sexually (see 428). |
| After sexual reproduction increased the rate of evolution, another development was a great bridge towards the evolution of life. What was it? | A few hundred million years after sexual reproduction started, multicellular organisms started developing from single-celled organisms. |
