Please read the following table in Markdown format and then answer the question according to the table. Table cells in one row are seperated by '|', and different rows are seperated by '
'.

Table:
| House name | House mascot | House colour | Year opened | House leader |
| --- | --- | --- | --- | --- |
| Hillary | Yeti | Green | 1980.0 | Mrs Wong |
| Kupe | Kiwi | Yellow | 1981.0 | Mr Goodyer |
| Rutherford | Elephant | Red | 1982.0 | Mr Morrisson |
| Mansfield | 'Dog' from Footrot Flats | Purple | 1984.0 | Mr Davidson |
| Te Kanawa | Taniwha | Blue | 1987.0 | Mr Norris |
| Batten | Buzzy Bee | White | 1998.0 | Ms Dorey |
| Snell | Black panther | Black | 2001.0 | Mr Mackenzie |
Question:
What is the earliest year a house opened?
Answer:
1980.0