The isotopes of carbon and oxygen reveal that the present climatic condition in northeastern Iowa (Stage 3) started about 3,600 years ago. Between 3,600 and 5,900 years ago, the vegetation was predominately prairie, the mean annual temperature was 3 degrees (C) warmer. The sharp change in oxygen isotopes suggest that climatic conditions changed in less than 50 years! From 5,900 to over 8,000 years ago conditions were similar to present, though warmer by approximately 1 degree (C).