The Fossil Record Tells the Story of Life
1. The planet Earth was formed 4.6 billion years ago.
2. Here are some major events in life's history
Single celled
life 4 billion years ago
Multicellular life 550 million years ago
1st human 0.1 million years ago
[---------------[-----------------------------------------------------------------[----[----------------[-----[>Today
Photosynthetic bacteria 3.5 billion years ago 1st land plant 500 million years ago 1st flowering plant 100 million years ago
If the history of life was on a 1 year calendar, than humans (Homo sapiens) appeared on Dec. 31st at
10 minutes to midnight.
3. Life's history can be divided into fours era. During the longest era, all life was single-celled. For a more detailed activity, go to the PBS website on Deep Time.
Precambrian era, 4 billion to 0.55 billion (550 million) years ago:
All life was single-celled organisms. Some developed the ability to
photosynthesize.
Paleozoic era: (550-250 million years ago)
Cambrian period is the first 50 million years of this era. Multicellular
life is suddenly seen in great abundance during this period called the Cambrian
explosion. Ancestors of all of today's life's forms are seen in these
fossils.
The first land plants arose during this era. Plants paved the way
for other forms of life to inhabit land since they start the food chain,.
Insects and amphibians were the earliest land animals.
Mesozoic era: (250-65 million years ago)
This is when dinosaurs roamed the Earth. At the end of this era, dinosaurs became extinct and flowering plants (angiosperms) appeared.
Cenozoic era (65 million years ago to present)
Mammals arise. Humans arise 100,000 years ago.
4. Extinctions
a. 99% of all species that lived are extinct (150 million
species)
b. Today: 1.5 million species are known of which half are
insects. Many more remain to be found.
New species are being discovered all the time. Even human ancestors are
being discovered such as
Ardipithecus ramidus.
c. We are living in period of mass extinctions. Thousands of species are wiped out every year
due to habitat destruction by humans. Many of these species have never been
seen. An example of habitat destruction would be cutting down rainforests to
sell wood.
d. Why care about species extinction if it is a natural event for species to disappear and
new species to arise?
Extinction and new species arising is a natural event over scales of tens of thousands of
years.. Since a human lifetime is about 100 years, what we wipe out is gone
for our life and nothing will arise to replace it. If we stopped destroying species tomorrow, it would take 5 million years to get back the
biodiversity we had in 1900.
5. Exercise: Your instructor may wish to use the Appendix from the Lab manual, constructing a timeline of life using fossils, in laboratory or class.