1920 - Milutin Milankovich
proposes that long term climatic cycles may be due to changes in the eccentricity
of the Earth's orbit and changes in the Earth's obliquity
1974 - Donald
Johanson and Tom Gray discover a 3.5 million-year-old female hominid fossil
that is 40% complete and name it "Lucy"
1980 - Luis Alvarez, Walter
Alvarez, Frank Asaro, and Helen Michel propose that a giant comet or asteroid
may have struck the Earth approximately 65 million years ago thereby causing
massive extinctions and enriching the iridium in the K-T
layer
1984 - Hou Xianguang discovers
the Chengjiang Cambrian fossil site
