Jane showed me some old pictures of the city as it looked 100 years ago.

as=when
此处为连词，表示时间当。。。时候。

At the same time that; while:
同时；当…时：
slipped on the ice as I ran home.
我跑回家时在冰上滑了一跤。

[表示时间]当..., 的时候 , 一边...一边, 随着
She sang As she worked.
她一边工作一边唱歌。
I saw him As he was getting off the bus.
正当他下公共汽车时, 我看见了他。
As a child, he lived in America.
他小时候住在美国。
You will grow wiser As you grow older.
随着你年令的增长, 你会变得更聪明。