You Know You Want To Know
Feed your curiosity about geology with these shots of the Earth, inside and out.
What killed off the trilobites
Trilobites had wild global success, roaming the early Paleozoic oceans for more than 270 million years and diversifying into a variety of forms and functions. Their diversity and wide distribution is why it ultimately took two mass extinctions to kill them off: the end-Devonian (~360 million years ago) and the end-Permian (~250 million years ago). Late Devonian sedimentary rocks preserve features of widespread ocean anoxia and rapid sequestration of carbon (e.g., as coal), as well as sea level changes that include a drastic, glacially-induced drop in sea level. Plants flourished on land for the first time during the Devonian, and it may be that their CO2 uptake and accelerated rock weathering led to (1) global cooling and (2) ocean eutrophication and anoxia due to the influx of soil nutrients. The early Paleozoic "Greenhouse" had shifted to a late Paleozoic "Icehouse." Just one order of trilobites survived this shift, the small, geographically widespread Proetida. Eventually, however, the Proetida were confined to mostly shallow-water environments, and as sea level dropped in the late Permian, so did their numbers. The end-Permian extinction killed off 95% of marine species, including the last remaining trilobites. Horsheshoe crabs may be the trilobites' closest living relatives.
What Zakynthos has to do with Florida
Navagio Beach on Zakynthos Island, where cigarette smugglers wrecked their ship during a chase in 1983, is framed by steep cliffs of Cretaceous limestone. In the Cretaceous, what is now Italy and Greece was called "Adria," a landmass the protruded from Africa into the Tethys Ocean, and was moving slowly northward toward the European continent. Adria was surrounded by warm, shallow seas where creatures built shells and reefs out of calcium carbonate (CaCO3), which eventually turned into limestone. These creatures prefer to live in clear water, far from river sediment. Because Adria was a peninsula, there were few large rivers dumping sediment into its shallow seas, and the carbonate "factory" kept going and going to form these thick limestone layers. Just like Florida today, which is surrounded by warm shallow seas and far from the sediment plumes of the Mississippi delta.
That the White Sands were twice dried
White Sands National Monument is a unique gypsum dune field in New Mexico, a wind-blown collection of selenite (a form of gypsum) that crystallized and eroded from nearby Lake Lucero when the lake dried out. It's really more of a re-birth of the gypsum, however, which originally formed back in the Permian more than 250 million years ago, when much of Texas and New Mexico was covered by tropical seas and carbonate reefs. The seas dried up in the middle Permian, and when the seawater was at 20% of its original volume, there were high enough concentrations of calcium (Ca2+) and sulfate (SO42-) to form gypsum (CaSO4*2H2O). Much later, these gypsum deposits were uplifted as part of the Rocky Mountains. Gypsum dissolves easily in rainwater, so during the rainy Pleistocene, streams draining the Rocky Mountain gypsum carried abundant Ca2+ and SO42- into the Lucero basin, which had no outlet. As the climate warmed after the last Ice Age, the lake dried up and the gypsum re-precipitated to be blown into the White Sands dune field.