strange dates in ROS' bags

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hello everyone. I'm trying to record the messages published to two topics inside a bag. The creation of .bag file is created correctly, but when I write

rosbag info subset.bag

this is what I get:

path:        subset.bag
version:     2.0
duration:    3:45s (225s)
start:       Jan 01 1970 01:36:56.10 (2216.10)
end:         Jan 01 1970 01:40:41.30 (2441.30)
size:        20.5 MB
messages:    4507
compression: none [28/28 chunks]
types:       nav_msgs/Odometry     [cd5e73d190d741a2f92e81eda573aca7]
             sensor_msgs/LaserScan [90c7ef2dc6895d81024acba2ac42f369]
topics:      /base_scan   2254 msgs    : sensor_msgs/LaserScan
             /odom        2253 msgs    : nav_msgs/Odometry

How is it possible that ROS saves messages as I had sent them in 1970? Thanks for help.