Table of contents

1. Introduction to Biology2h 42m
2. Chemistry3h 37m
3. Water1h 26m
4. Biomolecules2h 23m
5. Cell Components2h 26m
6. The Membrane2h 31m
7. Energy and Metabolism2h 0m
8. Respiration2h 40m
9. Photosynthesis2h 49m
10. Cell Signaling59m
11. Cell Division2h 47m
12. Meiosis2h 0m
13. Mendelian Genetics4h 44m
14. DNA Synthesis2h 27m
15. Gene Expression3h 6m
16. Regulation of Expression3h 31m
17. Viruses37m
- Viruses
  37m
18. Biotechnology2h 58m
19. Genomics17m
- Genomes
  17m
20. Development1h 5m
21. Evolution3h 1m
22. Evolution of Populations3h 53m
23. Speciation1h 37m
24. History of Life on Earth2h 6m
25. Phylogeny2h 31m
26. Prokaryotes4h 59m
27. Protists1h 12m
28. Plants1h 22m
29. Fungi36m
- Fungi
  19m
- Fungi Reproduction
  17m
30. Overview of Animals34m
- Overview of Animals
  34m
31. Invertebrates1h 2m
32. Vertebrates50m
33. Plant Anatomy1h 3m
34. Vascular Plant Transport1h 2m
- Water Potential
  1h 2m
35. Soil37m
- Soil and Nutrients
  20m
- Nitrogen Fixation
  16m
36. Plant Reproduction47m
- Flowers
  33m
- Seeds
  14m
37. Plant Sensation and Response1h 9m
38. Animal Form and Function1h 19m
39. Digestive System1h 10m
- Digestion
  1h 3m
- Blood Sugar Homeostasis
  7m
40. Circulatory System1h 49m
41. Immune System1h 12m
42. Osmoregulation and Excretion50m
- Osmoregulation and Excretion
  50m
43. Endocrine System1h 4m
- Endocrine System
  1h 4m
44. Animal Reproduction1h 2m
- Animal Reproduction
  1h 2m
45. Nervous System1h 55m
- Neurons and Action Potentials
  1h 8m
- Central and Peripheral Nervous System
  46m
46. Sensory Systems46m
- Sensory System
  46m
47. Muscle Systems23m
- Musculoskeletal System
  23m
48. Ecology3h 11m
49. Animal Behavior28m
- Animal Behavior
  28m
50. Population Ecology3h 41m
51. Community Ecology2h 46m
52. Ecosystems2h 36m
53. Conservation Biology24m
- Conservation Biology
  24m

24. History of Life on Earth

History of Life on Earth

General Biology

24. History of Life on Earth

History of Life on Earth

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Multiple Choice

Although they originated around 180 million years ago, mammals underwent an adaptive radiation starting approximately 65 million years ago. Why?

Mammals were not well adapted to the climate that existed before about 65 million years ago.

Mammals were mostly nocturnal until 65 million years ago.

Fur evolved in mammals around 65 million years ago, enabling them to withstand colder temperatures.

All of the listed responses are correct.

Between 180 and 65 million years ago, mammals were outcompeted by the well-established dinosaurs.

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Verified step by step guidance

Understand the concept of adaptive radiation: Adaptive radiation is the process by which organisms diversify rapidly into a multitude of new forms, particularly when changes in the environment make new resources available, create new challenges, or open new environmental niches.

Consider the timeline: Mammals originated around 180 million years ago but underwent significant adaptive radiation approximately 65 million years ago. This period coincides with the extinction of dinosaurs, which were dominant before this time.

Evaluate the environmental changes: Around 65 million years ago, a mass extinction event occurred, likely due to a catastrophic event such as an asteroid impact. This led to the extinction of dinosaurs, which had previously outcompeted mammals.

Analyze the ecological opportunities: With the extinction of dinosaurs, mammals had the opportunity to occupy ecological niches that were previously dominated by dinosaurs. This allowed mammals to diversify and adapt to various environments.

Conclude the reasoning: The adaptive radiation of mammals was primarily due to the removal of competition from dinosaurs, allowing mammals to explore and adapt to new ecological niches, rather than changes in climate or nocturnal behavior.