1. Unit 5 The History of Biological Diversity
Chapter 14
The History of Life

2. Fossil Evidence of Change
14.1 Essential Questions:
What are the similarities and differences between Earth’s early environment and Earth’s current environment?
What is a typical sequence of events in fossilization?
How are the different techniques for dating fossils used?
What are the major events on the geologic time scale?

3. Earth’s Early History Early Earth – 4 Billion Years Ago!
Very hot – somewhere around 15 billion Kelvin.
Lots of volcanoes and meteors.
No oxygen – just water vapor, H2, CO2 and N2.
About 3.9 Billion Years Ago…
Earth cooled and water condensed.
This led to millions of years of rain and lightning.
This could have filled the oceans.

4. Clues in Rocks
The earliest clues about life on Earth can be dated back about 3.5 billion years ago.
Fossils are any preserved evidence of an organism.
Only organisms that are quickly buried in sediment are able to be fossilized.
There are 6 kinds of fossils:

5. 6 Categories of Fossils
Trace Fossil – any indirect evidence such as footprints, burrows, feces (coprolite), etc.
Molds and Casts – a mold is an impression of an organism. A cast is a mold filled with sediment.
Replacement – the original organism is replaced with mineral crystals; very detailed.

6. Petrified or Permineralized – empty pore spaces are filled by minerals, ex: petrified wood.
Amber – tree sap taps an organism and hardens into amber.
Original Material – mummification or freezing preserves the original organism.

7. Dating Fossils
Relative Dating – uses layers of sediment/ rock to date fossils (like a stack of newspapers). The law of superposition states that young layers are on the top and older layers are on the bottom.

8. Radiometric Dating
Radioactive isotopes are atoms with unstable nuclei that break down over time and give off radiation.
Half Life - the time required for half of the atoms of a radioactive substance to become disintegrated
This breakdown happens in specific times and can be used like a clock.

9. The Geologic Time Scale
The Earth is estimated to be about 4.6 billion years old.
GTS is the record of Earth’s history.
Eon – the longest unit of time (billions of years)
Era – hundreds of millions of years
Periods – tens of millions of years
Epochs – several million years

11. On our calendar of 365 days a year…
Pre-Cambrian = January to mid-October
Paleozoic = Mid-October to December 9th
Mesozoic = December 10th to 25th
Cenozoic = December 26th on…
Man appeared on December 31st!!

12. Geologic Time Scale – 4 Eras
Pre-Cambrian – 87% of the earth’s history. Oldest fossils found from about 3.5 billion years ago…
Eukaryotes called Cyanobacteria and Stromatolites are most common.
At the end (544 million years ago) sponges and jellyfish fossils are found.

13. Geologic Time Scale – 4 Eras
Paleozoic – 540 to 245 million years ago. The earliest part is called the “Cambrian Period.”
The diversity of live increased! Invertebrates, early vertebrates, land plants, amphibians, seeded plants, reptiles and conifers appeared.
At the end, there was a major mass extinction. 90% of marine life and 70% of animal life disappeared.

14. Geologic Time Scale – 4 Eras
Mesozoic to 66 m.y.a. Continental drift happened – “Pangaea” broke apart to form our current continents.
This changed the habitats in which some organisms lived.
There was another large mass extinction during this era… a large meteorite hit in the Gulf of Mexico. 2/3rds of all species became extinct.

15. Geologic Time Scale – 4 Eras
Cenozoic – 66 million years ago to present.
Mammals began to flourish.
Primates appeared 30 million years ago
Humans appeared 200,000 years ago.

16. The Origin of Life 14.2 Essential Questions:
What are the differences between spontaneous generation and biogenesis?
What might have been the sequence of events that led to cellular life?
What is the endosymbiont theory?

17. The Origin of Life
Spontaneous Generation - the misinformed idea that nonliving material can produce life.
also called “abiogenesis”
a-without, bio-life, genesis-creation)
Examples: Meat produced maggots, mud made fish, and grain became mice.

18. Early Theories about Life
Francesco Redi (an Italian doctor in 1668) disproved spontaneous generation with a famous experiment.
Observation – everyone thinks meat makes maggots/flies.

19. Early Theories about Life
Anton Van Leeuwenhoek - Around 1684, he made and improved some of the first simple microscopes.
He discovered microscopic organisms like bacteria, protists, sperm cells, blood cells, nematodes and rotifers.

20. Early Theories about Life
Louis Pasteur – In the mid 1800’s he performed an experiment which supported BIOGENESIS (“life from life”).
Pasteurization: Pasteur discovered that heating milk to 135⁰F destroyed the dangerous microbes.
Pasteur discovered three bacteria strains: staphylococcus, streptococcus and pneumococcus.
This led to the basic rules of sterilization which revolutionized medicine.
He developed vaccines against chicken cholera, anthrax, swine disease, and rabies.

21. Where did life begin??
Alexander Oparin (1930’s) – hypothesized that life formed in the ocean.
Energy from the sun, lightning and earth’s heat helped to form the first macromolecules.
Rain washed the molecules into the ocean. This is often called “primordial soup”.

22. Where did life begin??
Stanley Miller and Harold Urey (1953) – recreated Oparin’s ideas in a lab setting.
Steam, ammonia, methane and hydrogen gases were combined (early atmosphere).
Electric current through the mix (lightning).
They then cooled the mixture and simulated rain.
After one week, they found several amino acids, sugars and other organic molecules.

23. Where did life begin??
Sidney Fox (1950’s) – American biochemist who showed how the first cells may have formed. He heated amino acids to form protocells.
Protocell – a large ordered structure that carries out some life activities such as growth and division.

24. Where did life begin??
Lynn Margulis (1960’s) – “Endosymbiont Theory” explained how prokaryotes could have become eukaryotes.
Prokaryote ingests aerobic bacteria. The bacteria were protected and produced energy for the cell.
These bacteria (aerobes) evolved into mitochondria and were no longer able to survive outside the cell → (Animal Cells)
Some primitive prokaryotes also ingested cyanobacteria which contained photosynthetic pigments.
The cyanobacteria became chloroplasts when they were no longer able to exist on their own → (Plant Cells)