In the last 66 million years, the climate of the Earth is known to have shifted abruptly between four different states; hothouse, warm house, cold house and icehouse. This was documented in 2020 by Westerhold et al. A further analysis of the data now leads to the conclusion that these abrupt climate changes often were preceded by early warning signals. In technical terms, a critical slowing down took place prior to most of the documented abrupt climate changes. Critical slowing down is typical behaviour of a physical system approaching a tipping point. The findings thus indicate that the Earth system likely tipped in the past.