Climate change 201 million years ago likely led to worldwide dinosaur dominance

Ooids from Cat Bay, Bahamas.
Microscope images from the published paper: A) Fragmented phosphatic coated grains. C) Light and dark brown concentric laminations. Red arrow points to unaltered shell fragment within the cortex of phosphatic coated grain. https://doi.org/10.1038/s41598-019-55162-2

Ooids

So how can ancient lake deposits tell the story of the mass extinction event that opened up an ecological niche for dinosaurs to thrive? To understand that, you need to know the geological context of the deposits, in particular, sediments called ooids (pronounced like it is spelled, oo-ids, where the ‘oo’ sounds like the ‘ue’ in blue). Ooids are small, round particles that form in shallow lakes or marine waters (for example, the Great Salt Lake in Utah and places in the Bahamas, see picture at top). The waters that ooids form in are basic (pH > 7) and rich in calcium carbonate (the minerals calcite and aragonite) or calcium phosphate (the mineral apatite). These deposits can form inorganically, that is through physical processes alone, or organically under the influence of living organisms. In the inorganic example, as water evaporates, the dissolved mineral components are unable to remain in solution and start to grow into crystals. In turbulent waters, rounded grains can form onion-like layers, representing growth rings. Sometimes bacteria can change the water chemistry, which enables biomineralization and forms round ooids, or larger pisoids or oncoids. Modern phosphate-rich ooids form in oxygen-minimum zones where bacteria help create the ooids by cycling between acidic/non-acidic and oxygenated/ deoxygenated waters. Determining if the inorganic evaporative process or the organic biomineralization process formed ancient ooids is a critical step in decoding past environs.

Changes in the water

By measuring the mineral, isotopic, and organic compositions of 201 million-year-old ooids, researchers were able to reconstruct the water chemistry of the lake in which these ooids formed. The ooids developed in low oxygen and slightly acidic shallow water. Interesting, the chemistry of this one lake is similar to the water chemistry of the deep ocean determined in previous research. This is significant because it may mean that much of the water (shallow or deep, lake or ocean) on Earth was extremely harsh for life, leading to a mass extinction.

Paleogeography and modern location of study localities. Samples sere taken from Williston Lake, in modern day British Columbia, Canada. The three sampling locations are shown in the the insert. Pangea is shown in green, and the CAMP volcanic area is outlined. https://doi.org/10.1038/s41598-019-55162-2

Outlook

The adaptation of life to specific climatic conditions and the response to climate change are considerable, and it doesn’t take much to disrupt a delicate balance. Geologists are similar to historians; we can only know the consequences of our current planetary changes by critically studying past events. The current climate change crisis is the only one in Earth’s history to be caused by humans, or even to be caused by life in general. We know what climate change can do and we know it is happening now. This is why many scientists think that we are moving toward (or even in) the 6th mass extinction event. The air is warming, the oceans are warming, waters are becoming more acidic, deoxygenation events are happening, biodiversity is already on the decline … all the signs are crystal clear.

Original Paper

Larina, E., Bottjer, D.J., Corsetti, F.A., Zonneveld, J., Celestian, A.J., Bailey, J.V. Uppermost Triassic phosphorites from Williston Lake, Canada: link to fluctuating euxinic-anoxic conditions in northeastern Panthalassa before the end-Triassic mass extinction. Sci Rep 9, 18790 (2019) doi:10.1038/s41598–019–55162–2

Keeping science accessible. Researching how minerals can be used to solve problems like climate change, pollution, and disease. @ NHMLA, USC, NASA-JPL