Friday Headlines, September 21, 2018
THE LATEST IN THE GEOSCIENCES
This week in geology
- 500 million year old cholesterol links us to one of the earliest animals
This week in the environment
- Reefs they are a’changin’
This fossil is one of the world’s earliest animals, according to fat molecules preserved for a half-billion years
The Ediacaran fauna includes many of the Earth’s oldest fossils and predates the time when multicellular organisms are often assumed to have rapidly diversified – the so-called “Cambrian Explosion.”
Most Ediacaran fossils are preserved as imprints in sediments. Their structures are interesting and unique, and scientists have struggled to determine whether they represent animals or plants.
This study examined two related Ediacaran taxa, Dickensonia and Andiva. Organic molecules (specifically steroids) were extracted from the impressions of the fossils and from adjacent non-fossiliferous rock. These steroids (the kinds and ratios between them) show fairly unambiguously that the fossils are those of animals and not of plants.
Climate change modifies the composition of reefs
Familiar coral reefs are composed of scleractinian or stony corals, organisms that build up heavy skeletons of calcium carbonate to support their bodies. These corals depend upon symbiotic algae for the majority of their food supply.
With the warming oceans, the symbiotic algae leave the corals, resulting in bleaching of the reef. The corals soon die without their symbionts.
As the scleractinian corals die back, they are being replaced by a more ancient type of coral called octocoral or gorgonian coral. These corals appear to cope with the warming waters better than scleractinian corals. However, they lack the heavy skeleton, resulting in a weaker reef that quickly falls apart under the pressure of waves.
Exactly why gorgonian corals can handle the warming ocean better than scleractinians is uncertain, but the loss of stony corals will weaken reefs, leaving shorelines more exposed to wave erosion.