How Did Life Begin?

2. How Did Life Begin? The Earth formed about 4.6 billion years ago according to evidence obtained by radiometric dating.

4. ½ life

5. The primordial soup model and the bubble model propose explanations of the origin of the chemicals of life. Scientists think RNA formed before DNA or proteins formed.

6. Bubble model

7. Scientists think that the first cells may have developed from microspheres. The development of heredity made it possible for organisms to pass traits to subsequent generations.

10. Complex Organisms Developed Prokaryotes are the oldest organisms and are divided into two groups, archaebacteria and eubacteria. Prokaryotes likely gave rise to eukaryotes through the process of endosymbiosis.

12. Mitochondria and chloroplasts are thought to have evolved through endosymbiosis. Multicellularity arose many times and resulted in many different groups of multicellular organisms. Extinctions influenced the evolution of the species alive today.

14. Life Invaded the Land Ancient cyanobacteria produced oxygen, some of which became ozone. Ozone enabled organisms to live on land. .

15. ozone

16. Plants and fungi formed mycorrhizae and were the first multicellular organisms to live on land

17. fungi

18. Arthropods were the first animals to leave the ocean.

20. The first vertebrates to invade dry land were amphibians. The extinction of many reptile species enabled birds and mammals to become the dominant vertebrates on land.

21. The movement of the continents on the surface of the Earth has contributed to the geographic distribution of some species.

22. The fossil record also provides an amazing amount of evidence concerning common ancestors. Fossilized remains of invertebrates (animals without an internal skeleton), vertebrates, and plants appear in the strata or layers of Earth's surface in the same order that the complexities of their anatomy suggest.

23. The more evolutionarily distant organisms lie deeper, in the older layers, beneath the remains of the more recent organisms. Geologists are able to date rock strata with reasonable accuracy, and the age of a layer always correlates with the fossils discovered there. In other words, there would never be a stratum dating back 400 million years that contained fossils of mastodons, which evolved much later.

26. The Theory of Evolution by Natural Selection ● Charles Darwin concluded that animals on the coast of South America that resembled those on the nearby islands evolved differences after separating from a common ancestor.

27. Darwin’s trip

31. camouflage

33. ● Darwin was influenced by Thomas Malthus, who wrote that populations tend to grow as much as the environment allows.

34. ● Darwin proposed that natural selection favors individuals that are best able to survive and reproduce.

35. ● Under certain conditions, change within a species can lead to new species. ●

36. Evidence of Evolution ● Evidence of orderly change can be seen when fossils are arranged according to their age. ● ● Similarities of structures in different vertebrates provide evidence that all vertebrates share a common ancestor.

37. Though their ancestors ceased to walk on four legs many millions of years ago, snakes still possess vestigial hind limbs as well as reduced hip and thigh bones.

38. In some cases widely divergent organisms possess a common structure, adapted to their individual needs over countless generations yet reflective of a shared ancestor. A fascinating example of this is the pentadactyl limb, a five-digit appendage common to mammals and found, in modified form, among birds. The cat's paw, the dolphin's flipper, the bat's wing, and the human hand are all versions of the same original, an indication of a common four-footed ancestor that likewise had limbs with five digits at the end.

39. Homologous structures

40. The embryonic forms of animals also reflect common traits and shared evolutionary forebears. This is why most mammals look remarkably similar in early stages of development. In some cases animals in fetal form will manifest vestigial features reflective of what were once functional traits of their ancestors.

41. Differences in amino acid sequences and DNA sequences are greater between species that are more distantly related than between species that are more closely related.

45. Examples of Evolution ● Individuals that have traits that enable them to survive in a given environment can reproduce and pass those traits to their offspring. ●

47. Industrial Melanism and the Pepper Moth • Both natural selection and mutation play a role in industrial melanism, a phenomenon whereby the processes of evolution can be witnessed within the scale of a human lifetime. • Industrial melanism is the high level of occurrence of dark, or melanic, individuals from a particular species (usually insects) within a geographic region noted for its high levels of dark-colored industrial pollution.

48. With so much pollution in the air, trees tend to be darkened, and thus a dark moth stands a much greater chance of surviving, because predators will be less able to see it. • At the same time, there is a mutation that produces dark-colored moths, and in this particular situation, these melanic varieties are selected naturally. • On the other hand, in a relatively unpolluted region, the lighter-colored individuals of the same species tend to have the advantage, and therefore natural selection does not favor the mutation.

49. The best-known example of industrial melanism occurred in a species known as the pepper moth, or Biston betularia, which usually lives on trees covered with lichen. • Prior to the beginnings of the Industrial Revolution in England during the late eighteenth century, the proportion of light-colored pepper moths was much higher than that of dark-colored ones, both of which were members of the same species differentiated only by appearance