View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Apollo Hypoxia, Fetal & Neonatal Physiology: 100 years on from Sir Joseph Barcroft 1D A Giussani, 2L Bennet, 1A N Sferruzzi-Perri, 1O R Vaughan & 1AL Fowden 1Department of Physiology, Development & Neuroscience, University of Cambridge, Cambridge, CB2 3EG, UK 2The Department of Physiology, University of Auckland, Auckland, New Zealand Journal: Journal of Physiology Submission: Editorial Correspondence: Professor Dino A Giussani, Ph.D. Department of Physiology Development & Neuroscience Downing Street University of Cambridge Cambridge CB2 3EG UK Tel: +44 1223 333894 E-mail:
[email protected] 1 1 During the history of the Earth there have been dramatic changes in its oxygen 2 (O2) availability (Graham et al. 1995). Geochemical models suggest that in the 3 mid-to-late Devonian era (ca. 380 million years ago, mya), O2 levels in the Earth’s 4 atmosphere increased from ~18 to 20%. By the late Carboniferous period (286 5 mya), the Earth’s oxygenation had risen sharply to ~35%, which palaeontologists 6 refer to as ‘the oxygen pulse’. Through the following Permian and Palaeozoic eras, 7 approximately 250 mya ago, O2 concentrations fell to ~11%. Thereafter, in the last 8 200 million years, O2 levels steadily increased again, settling at the present day 9 level of ~21%. 10 11 These fluctuations in O2 availability have shaped the evolution of animal life on 12 Earth and are one of the earliest challenges in physiological history. When O2 13 availability increased animals harnessed this new fuel and grew larger irrespective 14 of their phyla.