Evolution: Change Over Time Notes

Learning Target: What is Evolution and How Is It Studied?

• Extensive evidence indicates life on Earth began 3 billion years ago.
• Fossils in ancient rocks provide clues about past life.
• Early life forms were simple, single-celled organisms.
• Over time, more complex single-celled organisms developed.
• About a billion years ago, complex multicellular organisms appeared.
• Evolution explains the change in species over time.

The Theory of Evolution

• The Theory of Evolution is a central theme in modern biology.
• It explains how variations among individuals lead to changes in a species.
• Charles Darwin first suggested the concept of evolution.
• Evolution has been refined by evidence from thousands of scientists.
• The extensive evidence validates evolution as a Theory:
  • It's been tested and confirmed in different ways.
  • Scientists use it to make predictions about the natural world.

Example of Evolution: The Horse

• Eohippus is an ancient ancestor of the horse.
  • It was about the size of a fox.
  • It had 4 toes on its front feet and 3 toes on its hind feet.
• As the Eohippus evolved:
  • It got bigger.
  • The length of its feet increased.
  • Surrounding toes shrank.
  • The modern horse retained one large middle toe (the hoof) and two tiny splints.
• The modern horse is a one-toed Equus.

Fossil Evidence of Horse Evolution

• Fossils show the gradual loss of toes from Eohippus to the modern horse, leading to a more efficient hoof.
• The skull grew longer.
• The teeth became flat-topped.

Studying Evolution

• The Theory of Evolution helps biologists understand similarities among different organisms (e.g., bone structure, biochemistry).
• It explains the history of life revealed by the fossil record.
• The fossil record is a collection of fossils providing clues to the history of Earth's organisms.
• The fossil record spans much of Geologic Time, revealing changes in environment and species.

Geologic Time

• Earth is estimated to be 4.5 billion years old.
• Life began with simple, single-celled organisms.
• Increasingly complex, multicellular organisms evolved over time.
• Geologic time divides EONS into ERAS for easier study.
• ERAs are further divided into PERIODS.

Geologic Timeline

• Hadean Eon:
  • $3,800-4,600$ million years ago
  • Formation of the Earth.
• Archean Eon:
  • $2,500$ million years ago
  • Formation of the continents.
  • Early life (bacteria, archaeans).
• Proterozoic Eon:
  • $570$ million years ago
  • First sponges, colonial algae, and soft-bodied invertebrates.
• Paleozoic Era:
  • Cambrian Period: $543$ million years ago; Rise of all major animal groups.
  • Ordovician Period: $505$ million years ago; Echinoderms, bryozoans dominant in oceans.
  • Silurian Period: $440$ million years ago; First land plants, primitive fungi, seaweed appear.
  • Devonian Period: $410$ million years ago; First spiders, scorpions, centipedes, early insects, vascular plants, jawed fish and large reefs appear.
  • Carboniferous Period:
    • Mississippian Period: $360$ million years ago
    • Pennsylvanian Period: $325$ million years ago; First amphibians, first reptiles, cockroaches and mayflies appear.
  • Permian Period: $286$ million years ago; Major extinction of $95$% of marine species and $50$% of all animal families.
• Mesozoic Era:
  • Triassic Period: $245$ million years ago; Origin of mammals, dinosaurs and true flies.
  • Jurassic Period: $208$ million years ago; Dinosaurs and gymnosperms dominate the land.
  • Cretaceous Period: $146$ million years ago; Marsupials, ants, bees, butterflies, flowering plants appear; Mass extinction of most large animals and many plants.
• Cenozoic Era:
  • Tertiary Period: $50$ million years ago; Apparition of all mammals.
  • Quaternary Period: $1.8$ million years ago; Modern humans appear; Four major glaciations cause rapid shifts in ecological communities.

Definition of Evolution

• Evolution is the change in species over a long period of time.

Best Description of Evolution

• A process of change in species over a period of time. Note this is the best answer in the multiple choice question. Other answers might seem plausible but this aligns most closely with the definition and details provided.