The Messinian salinity crisis is widely regarded as one of the most dramatic episodes of oceanic change of the past 20 or so million years (refs 1±3). Earliest explanations were that extremely thick evaporites were deposited in a deep and desiccated Mediterranean basin that had been repeatedly isolated from the Atlantic Ocean 1,2 , but elucidation of the causes of the isolationÐwhether driven largely by glacio-eustatic or tectonic processesÐhave been hampered by the absence of an accurate time frame. Here we present an astronomically calibrated chronology for the Mediterranean Messinian age based on an integrated high-resolution stratigraphy and`tuning' of sedimentary cycle patterns to variations in the Earth's orbital parameters. We show that the onset of the Messinian salinity crisis is synchronous over the entire Mediterranean basin, dated at 5:96 6 0:02 million years ago. Isolation from the Atlantic Ocean was established between 5.59 and 5.33 million years ago, causing a large fall in Mediterranean water level followed by erosion (5.59±5.50 million years ago) and deposition (5.50±5.33 million years ago) of non-marine sediments in a large`Lago Mare' (Lake Sea) basin. Cyclic evaporite deposition is almost entirely related to circum-Mediterranean climate changes driven by changes in the Earth's precession, and not to obliquity-induced glacio-eustatic sea-level changes. We argue in favour of a dominantly tectonic origin for the Messinian salinity crisis, although its exact timing may well have been controlled by the ,400-kyr component of the Earth's eccentricity cycle.Most hypotheses about the initiation of the Messinian salinity crisis (MSC) agree that it resulted from a complex combination of tectonic and glacio-eustatic processes which progressively restricted and ®nally isolated the Mediterranean Sea from the open ocean 1±8 . The gradual modi®cation of water exchange with the Atlantic caused important palaeoceanographic changes in the Mediterranean. This is re¯ected in the classic Messinian sequence of Sicily 9 which starts at 7.24 Myr ago (ref.3) with alternations of open marine marls and sapropels, passes via diatomites into the Lower Evaporites (gypsum, evaporitic limestone and halite), and ends, above an erosional surface, with the Upper Evaporites (gypsum, marls) and fresh to brackish water deposits of Lago Mare facies.Here we de®ne the MSC as the interval of evaporite deposition and Lago Mare sedimentation in the Mediterranean before the Pliocenē ooding 5.33 Myr ago 10 . Controversies still exist, however, over the timing and duration of the MSC; these range from a synchronous event 1 (that is, onset of the MSC in all basins at the same time) to a two-step event 4 (onset of MSC ®rst in marginal basins and later in deep basins) to a completely diachronous evolution 5 (onset of MSC totally dependent on local basinal setting). Equally large controversies exist over the cause, and the effects, of the isolation of the Mediterranean; the two basic explanations are (1) a large glacio-eustatic sea-level drop, r...

Calibration of the geological time scale is achieved by independent radioisotopic and astronomical dating, but these techniques yield discrepancies of approximately 1.0% or more, limiting our ability to reconstruct Earth history. To overcome this fundamental setback, we compared astronomical and 40Ar/39Ar ages of tephras in marine deposits in Morocco to calibrate the age of Fish Canyon sanidine, the most widely used standard in 40Ar/39Ar geochronology. This calibration results in a more precise older age of 28.201 +/- 0.046 million years ago (Ma) and reduces the 40Ar/39Ar method's absolute uncertainty from approximately 2.5 to 0.25%. In addition, this calibration provides tight constraints for the astronomical tuning of pre-Neogene successions, resulting in a mutually consistent age of approximately 65.95 Ma for the Cretaceous/Tertiary boundary.

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Continental aridification and the intensification of the monsoons in Asia are generally attributed to uplift of the Tibetan plateau and to the land-sea redistributions associated with the continental collision of India and Asia, whereas some studies suggest that past changes in Asian environments are mainly governed by global climate. The most dramatic climate event since the onset of the collision of India and Asia is the Eocene-Oligocene transition, an abrupt cooling step associated with the onset of glaciation in Antarctica 34 million years ago. However, the influence of this global event on Asian environments is poorly understood. Here we use magnetostratigraphy and cyclostratigraphy to show that aridification, which is indicated by the disappearance of playa lake deposits in the northeastern Tibetan plateau, occurred precisely at the time of the Eocene-Oligocene transition. Our findings suggest that this global transition is linked to significant aridification and cooling in continental Asia recorded by palaeontological and palaeoenvironmental changes, and thus support the idea that global cooling is associated with the Eocene-Oligocene transition. We show that, with sufficient age control on the sedimentary records, global climate can be distinguished from tectonism and recognized as a major contributor to continental Asian environments.

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