1. Geologic Time

2. Earth is about 4.6 billion years old
no life for about the first two billion years
bacteria were first life to appear
no oxygen in atmosphere for the next 1-2 billion years
when oxygen was in the atmosphere, life began to flourish
Homo sapiens only here for about 200,000 years

3. What is the Earth’s time scale?
The Geological time scale is a record of the life forms and geological events in Earth’s history.
Scientists developed the time scale by studying rock layers and fossils world wide.
Radioactive dating helped determine the absolute divisions in the time scale.

4. The Geologic Time Scale
Divided into blocks of time called eons, eras and periods.

5. Broken down Based on events, not number of years

6. Divisions of Geologic Time
Geological time begins with Precambrian Time. Precambrian time covers approximately 88% of Earth’s history.

7. Paleozoic Era
Lasted from 542 to 251 mya.

8. (AKA the “Age of Reptiles”.)
Mesozoic Era
Lasted from 251 to 65 mya
(AKA the “Age of Reptiles”.)

9. Cenozoic Era Began 65 mya and is still going on
(AKA the Age of Mammals).

10. Mass Extinction
Scientists have evidence that a large asteroid crashed near Mexico’s Yucatan peninsula about 65 mya.
The resulting climate change may have caused the extinction of Mesozoic Era reptiles, including most dinosaurs.

11. Trees and Absolute Dating
Trees are like history books.
Each tree ring is a record of what the environment was like that year.
Wide tree rings indicated a very wet year and narrow rings indicated a dry year.

12. FYI – oldest plants
The oldest tree on record is a bristlecone pine called “Methuselah.”
It is 4,765 years old.
Gallery
Ted Talk – oldest living organisms

13. Overview of Dating Relative dating
is a method of sequencing events in the order they happened
they do not tell us when an event happened

14. Which event happened first?

16. Absolute dating
a method of measuring the age of an object such as a rock or fossil in years
tree ring data is very accurate
a tree grows one tree ring for every year that it is alive
unfortunately, only can go back 5,000 at the most

17. radiometric dating measures changes in atoms resulting from radioactivity
compares the # of radioactive isotopes that are in the object now, to what it had before
provides us with a reliable clock that is unaffected by normal forces in nature

18. carbon dating upper limit is about 50,000 years
How Carbon-14 Dating Works (1:07)
Carbon dating (2:10)

19. uranium dating
upper limit is billions of years old

20. The Changing Earth
most of the land on Earth was part of a large landmass called Pangea about 250 millions of years ago

21. during a period of about 250 million years, Pangaea broke apart (continental drift)

22. Plate Tectonics Tectonic plates
large pieces of the crust and part of the mantle called the lithosphere
seven very large ones and lots of small ones
constantly moving/floating (1-16cm/year) on the plastic part of the mantle because of convection currents in the soft rock underneath them
this is called continental drift

26. Earth 100 Million Years From Now (3:19)
650 Million Years in under 2 minutes (1:20)
Earth's history in the last 600 million years (1:37)

29. For most recent EQ -- http://www.pnsn.org/recenteqs/latest.htm

31. Warming/Cooling Trends
scientists analyze tiny air bubbles trapped in ice cores to learn about past:
atmospheric CO2 concentration has increased over 25% over the last few centuries
this increase correlates with increase of Earth’s temperatue
Siple Station, Antarctica
75°55' S, 83°55' W