 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
 is a method of sequencing events in the
order they happened
 they do not tell us when an event happened
Which event happened first?
 a method of measuring the age of an
object such as a rock or fossil in years
1. 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
2.
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
 carbon dating
 upper limit is about 50,000 years
 How Carbon-14 Dating Works (1:07)
 Carbon dating (2:10)
 uranium dating
 upper limit is billions of years old
 most of the land on Earth was part of a large
landmass called Pangea about 250 millions of
years ago
 during a period
of about 250
million years,
Pangaea broke
apart
(continental
drift)
 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
 Earth 100 Million Years From Now (3:19)

http://www.youtube.com/watch?v=uGcDed4xVD4
&feature=fvwrel
 650 Million Years in under 2 minutes (1:20)

http://www.youtube.com/watch?v=NYbTNFN3NB
o&feature=related
 Earth's history in the last 600 million years
(1:37)

http://www.youtube.com/watch?v=cQVoSyVu9rk
&feature=related
For most recent EQ -- http://www.pnsn.org/recenteqs/latest.htm
 scientists
analyze tiny air bubbles trapped
in ice cores to learn about past:
 atmospheric
CO2 concentration in 1750 was
280 ppm and that it increased by 22% to 345
ppm in 1984
Siple Station, Antarctica
75°55' S, 83°55' W