Uniformitarianism permits understanding of the past on the basis of the present, and modeling the future through consideration of the fossil record. The present paper addresses the impact environmental (climatic) change has had on acorn barnacles and eucalyptus trees. Acorn barnacles (Balanomorpha) are first recorded after the K/T mass-extinction event. In the Paleogene, rapid radiation resulted in their occupying most marine environments. That balanomorphs survived both the Paleocene–Eocene thermal maximum and the Pleistocene glaciation is testament to their ability to adapt to opportunities; they are known from the littoral (Chamaesipho) to depths of 3600 m (Tetrachaelasma) and within this from diverse substrates: rock, wood and miscellaneous flotsam, plus in symbiosis or commensalism with most larger marine organisms. Darwin's (1854) view of the late Tertiary as the age of barnacles is reflected in their diversity, distribution and biomass. Barnacles are contrasted with the Australian Myrtaceae: plants ranging from woody shrubs to tall trees. The most significant is Eucalyptus sensu lato, which typifies Australia's flora, and is characterized by aromatic leaves that produce eucalyptol. Eucalyptus has evolved strategies that result in its domination of Australian open woodlands: these include production of highly flammable eucalyptol oil (with a flashpoint of 49 °C) and an unprecedented ability to regenerate following forest fires. Gum trees and barnacles first appear in the Paleogene, their earliest records are Australasian, and they both demonstrate extraordinary resilience when environmental conditions are optimal.