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

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

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

4. Trace fossils record the activity of an organism.

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

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

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

8. 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 placement of fossils in layers of rock.
Scientists infer the order in which species existed.

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

10. 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.

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

12. 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.

13. The geologic time scale organizes Earth’s history.
The history of Earth is represented in the geologic time scale.
100
250
550
1000
2000
PRECAMBRIAN TIME
Cyanobacteria
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.

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

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

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

17. 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.

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

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

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

21. 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.

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

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

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

25. Trace fossils record the activity of an organism.

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

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

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

29. 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 placement of fossils in layers of rock.
Scientists infer the order in which species existed.

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

31. 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.

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

33. 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.

34. The geologic time scale organizes Earth’s history.
The history of Earth is represented in the geologic time scale.
100
250
550
1000
2000
PRECAMBRIAN TIME
Cyanobacteria
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.

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

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

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

38. 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.

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

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

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

42. 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.

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

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

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

46. 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.

47. 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.

48. KEY CONCEPT Multicellular life evolved in distinct phases.

49. 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.

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

51. 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.

52. 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.

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

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

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

56. 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.

57. Bipedal means walking on two legs.
foraging
carrying infants and food
using tools
Walking upright has important adaptive advantages.

58. 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.

59. 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.
Australopithecus
afarensis
Homo habilis
Homo
neanderthalensis
Homo sapiens