TEMPERATURE OF THE EARTH IN TIME AND SPACE 9 



sequent diminution of temperature on the earth. Such 

 changes occurred after both eruptions of Krakatau 

 (1884-1886; 1903-1904). 



The Capture of Solar Radiation. — The internal heat 

 of the earth's mass and the heat converted from radiant 

 energy are sufficient to create a favorable physical en- 

 vironment for life on the earth's surface. Life, however, 

 could not have evolved to the complexity of organization 

 manifested today in animals, and especially could not 

 have climbed the phylogenetic tree to the branches occu- 

 pied by the homoiothermic animals, save by the capture 

 of sunlight. 



In warming the earth's surface the energy of sunlight 

 is converted directly from electronic energy to molecular 

 energy. Living matter has found a way by which the 

 energy of sunlight may be stored or conserved and trans- 

 lated into molecular energy at some future time when it 

 will better serve the organism. Thus there seems to be 

 a system of conservation of energy in living matter — 

 almost a closed cycle of energy changes. The energy of 

 sunlight is captured on one side of this cycle to compen- 

 sate for the loss of energy on the other. This captured 

 energy enters the prison gates of living substance 

 through chlorophyll. It is transformed and mobilized to 

 places where it awaits release. Thus living substance is 

 not only a transformer of energy but an accumulator as 

 well. Once energy has accumulated, plants and animals 

 become reciprocating transformers of it, so that the 

 energy wastes of one become the energy sources of the 

 other. This matter will receive more detailed treatment 

 in later chapters. 



