Evolution of Life on Earth: Fossils, Time Scale, and Human Origins

1. KEY CONCEPT Specific environmental conditions are necessary in order for fossils to form.

2. KEY CONCEPT The geologic time scale divides Earth’s history based on major past events.

3. KEY CONCEPT The origin of life on Earth remains a puzzle.

4. KEY CONCEPT Single-celled organisms existed 3.8 billion years ago.

5. KEY CONCEPT Multicellular life evolved in distinct phases.

6. KEY CONCEPT Humans appeared late in Earth’s history.

7. Humans share a common ancestor with other primates. • Primates are mammals with flexible hands and feet, forward-looking eyes and enlarged brains.

8. Prosimians are the oldest living primates. • They are mostly small and nocturnal. • Primates evolved into prosimians and anthropoids.

9. Anthropoids are humanlike primates. • They are subdivided into the New World monkeys, Old World monkeys, and hominoids. • Homonoids are divided into hominids, great apes, and lesser apes. • Hominids include living and extinct humans.

10. foraging • carrying infants and food • using tools • Walking upright hasimportant adaptiveadvantages. • Bipedal means walking on two legs.

11. There are many fossils of extinct hominids. • Most hominids are either the genus Australopithecus or Homo. • Australopithecines were a successful genus. • The Homo genus first evolved 2.4 million years ago.

12. Australopithecus afarensis Homo habilis Homo neanderthalensis Homo sapiens Modern humans arose about 200,000 years ago. • Homo sapiens fossils date to 200,000 years ago. • Human evolution is influenced by a tool-based culture. • There is a trend toward increased brain size in hominids.

13. Life moved onto land during the Paleozoic Era. • Multicellular organisms first appeared during the Paleozoic era. • The era began 544 million years ago and ended 248 million years ago. • The Cambrian explosion led to a huge diversity of animal species.

14. Life moved onto land in the middle of the Paleozoic era.

15. Reptiles radiated during the Mesozoic era. • The Mesozoic era is known as the Age of Reptiles. • It began 248 million years ago and ended 65 million years ago. • Dinosaurs, birds, flowering plants, and first mammals appeared.

16. Mammals radiated during the Cenozoic era. • The Cenozoic era began 65 million years ago and continues today. • Placental mammals and monotremes evolved and diversified. • Anatomically modern humans appeared late in the era.

17. Microbes have changed the physical and chemical composition of Earth. • The oldest known fossils are a group of marine cyanobacteria. • prokaryotic cells • added oxygen toatmosphere • deposited minerals

18. Fossil stromatolites provide evidence of early colonies of life.

19. Eukaryotic cells may have evolved through endosymbiosis. • Endosymbiosis is a relationship in which one organism lives within the body of another. • Mitochondria and chloroplasts may have developed through endosymbiosis.

20. The evolution of sexual reproduction led to increased diversity. • Genetic variation is an advantage of sexual reproduction. • Sexual reproduction may have led to the evolution of multicellular life.

21. Earth was very different billions of years ago. • There have been many hypotheses of Earth’s origins. • The most widely accepted hypothesis of Earth’s origins is the nebula hypothesis.

22. electrodes “atmosphere” water “ocean” heat source amino acids Several sets of hypotheses propose how life began on Earth. • There are two organic molecule hypotheses. • Miller-Urey experiment • meteorite hypothesis

23. iron-sulfide bubbles hypothesis • There are different hypotheses of early cell structure.

24. lipid membrane hypothesis • There are different hypotheses of early cell structure.

25. A hypothesis proposes that RNA was the first genetic material. • Ribozymes are RNA molecules that catalyze their own replication. • DNA needs enzymes to replicate itself.

26. Index fossils are another tool to determine the age of rock layers. • Index fossils can provide the relative age of a rock layer. • existed only during specific spans of time • occurred in large geographic areas • Index fossils include fusulinids and trilobites.

27. 100 250 550 1000 2000 PRECAMBRIAN TIME This time span makes up the vast majority of Earth’s history. It includes the oldest known rocks and fossils, the origin of eukaryotes, and the oldest animal fossils. Cyanobacteria The geologic time scale organizes Earth’s history. • The history of Earth is represented in the geologic time scale.

28. consist of two or more periods • three eras: Cenozoic, Mesozoic, Paleozoic • Eras last tens to hundreds of millions of years.

29. most commonly used units of time on time scale • associated with rock systems. • Periods last tens of millions of years. • Epochs last several million years.

30. Fossils can form in several ways. • Permineralization occurs when minerals carried by water are deposited around a hard structure.

31. A natural cast forms when flowing water removes all of the original tissue, leaving an impression.

32. Trace fossils record the activity of an organism.

33. Amber-preserved fossils are organisms that become trapped in tree resin that hardens after the tree is buried.

34. Preserved remains form when an entire organism becomes encased in material such as ice.

35. Only a tiny percentage of living things became fossils. • Specific conditions are needed for fossilization.

36. Radiometric dating provides an accurate way to estimate the age of fossils. • Relative dating estimates the time during which an organism lived. • It compares the placementof fossils in layers of rock. • Scientists infer the order inwhich species existed.

37. protrons neutrons • Isotopes are atoms of an element that differ in their number of neutrons. • Radiometric dating uses decay of unstable isotopes.

38. Radiometric dating uses decay of unstable isotopes. • Isotopes are atoms of an element that differ in their number of neutrons. • A half-life is the amount of time it takes for half of the isotope to decay.