i want to copy a first column from a file(.txt) and replace it with first column of second file in text delimited using Unix code. kindly help

input file format 
file 1

    01/01/2007
    02/01/2007
    03/01/2007
    04/01/2007

file 2

    20070101 10.2317  79.1638   6.0  26.7  20.9   0.8  14.0  98.6
    20070102 10.2317  79.1638   5.6  26.5  20.8   1.9  13.6  98.0
    20070103 10.2317  79.1638   7.5  27.7  20.8   0.1  15.8  96.4
    20070104 10.2317  79.1638   8.1  26.0  19.6   0.0  15.5  94.1

out put required 

    01/01/2007  10.2317   79.1638   6.0  26.7  20.9   0.8  14.0  98.6
    02/01/2007  10.2317   79.1638   5.6  26.5  20.8   1.9  13.6  98.0
    03/01/2007  10.2317   79.1638   7.5  27.7  20.8   0.1  15.8  96.4
    04/01/2007  10.2317   79.1638   8.1  26.0  19.6   0.0  15.5  94.1