Ancient reef and reefs through time

What has been a feature of coastal oceans for nearly as long as there has been life on earth?

reefs

What has been a feature of reefs since the beginning of time?

photosynthesis

What has changed many times?

the types of organisms that have built reefs?

What has caused the types of organisms who have built reefs to change?

mass extinctions, evolution of community ecology, changes in sea levels, tectonics, and changes in the ocean geochemistry

what is the study of the chemical composition of sea water, ocean sediments, and the marine crust, as well as the chemical processes and cycles that shape them

ocean geochemistry

What period of reefs occurred 3.4-0.54 billion years ago?

Precambrian reefs

how were precambrian reefs formed before multicellular organisms?

by photosynthetic cyanobacteria

What did the photosynthetic cyanobacteria produce?

stromatolites

How are stromatolites formed?

built by cyanobacteria through microbial mats trapping sand silt and minerals which are cemented and then the microbes migrate upward to stay in the sunlight and the process happens again

What are stomatolites?

stromatolites are layered rock like sedimentary structures

What period of reefs occurred 541-443 million years ago?

Early Paleozoic reefs

What built early paleozoic reefs?

Archaeocythid sponges

Did the archaeocyathic sponges have photosynthetic symbionts?

they may have

What was a trait of early paleozoic reefs?

many growth forms

What led to the extinction of early paleozoic reefs?

sea level rise, high co2 and global warming

What happened during the early paleozoic reefs era?

the Great Ordovician Biodiversification Event

What was the Great Ordovician Biodiversification event?

a diversification of reef-building biota that was biologically driven rather than being driven by environmental change

What organisms became reef builders after the Great Ordovician Biodiversification Event?

bryozoans, sponges (lithistid sponges and stomatoporoids), brachipods, and rugose corals

What appeared during this time but didn’t start building reefs until the end of the Ordovician?

Tabulate corals

What corals are solitary and colonial, have well-defined septa, well-defined tabula, are often horn-shaped and have calcite skeletons?

Rugose corals

What corals are nearly always colonial, have poorly defined septa, well-defined tabula, and calcite skeletons?

Tabulate corals

What are the main differences between rugose and tabulate corals?

rugose can be both solitary and colonial and have well defined septa, while tabulate corals are nearly always colonial and have poorly defined septa.

What appears during the Mid-Paleozoic?

the first coral reef ecosystems

What geologic era was 443-359 million years ago?

the Mid-Paleozoic

What association dominated on coral reef ecosystems during the Mid-Paleozoic?

coral-stromotoporoid-algae association

What geologic era had a super greenhouse Earth?

Mid-Paleozoic

what is a supergreenhouse Earth?

An extreme climate state in earth’s geologic history characterized by drastically elevated greenhouse gas concentrations, severely elevated temperatures, and near-total or complete absence of polar ice sheets

What latitudes did reefs grow at in the Mid-Paleozoic?

55 degrees latitude

Were reefs much larger in the Mid-Paleozoic than today?

yes reefs were much larger

What wiped the reefs out in the Mid-Paleozoic?

the Devonian mass extinction

What is likely to have caused the Devonian mass extinction?

climate change

Which geologic era contained reefs that has large colonies of tabulate and rugose corals, crinoids, bryozoans, and brachipods?

the middle silurian during the mid-late paleozoic

Which geologic era occurred 359-252 million years ago?

the Late Paleozoic

What happened to reefs during the late paleozoic

reefs diversified but struggled until the permian extinction?

Did the late paleozoic have calcite or aragonite seas?

aragonite seas

What was the largest mass extinction to hit marine ecosystems?

the permian extinction

What happened during the permian extinction to corals?

rugose and tabulate corals were wiped out alongside stromatoporoids and the reefs they built

What was likely to have caused the permian extinction?

volcanism contributing CO2 to the atmosphere and oceans, dramatic warming, acidification, and anoxia

what is anoxia?

Total absence of dissolved oxygen in water, soil, or sediment

What geologic era occurred 252-66 million years ago?

the Mesozoic

What did we see for reefs during the mesozoic?

the first modern reefs

How long were the reefs gone after the permian extinction?

about 8 million years

What was atmospheric CO2 like during the Mesozoic?

huge fluctuation in atmospheric CO2

What did this huge fluctuation of atmospheric CO2 in the Mesozoic cause?

lots of little diversifications and extinctions?

When do the first scleractinians arrive during the Mezoic?

during the middle triassic

When do the scleractinians that arrive during the Mesozoic start building reef?

during the Late Triassic

During the jurassic-cretaceous transition what appear and build reefs with corals?

rudists

How long do corals and rudist bivalves build reefs for?

millions of years

What happened with rudists in the early Cretaceous during the Mesozoic?

they replace corals mysteriously

What type of seas did the cretaceous period in the Mesozoic have?

calcite

What were rudist bivalves?

mollusks

did rudist bivalves have algal symbionts?

yes

what types of shells did rudists have?

both calcite and aragonite

What happened to both rudists and reefs at the end of the Cretaceous during the Mesozoic?

they were wiped out by a meteor impact

What period was 66-0 million years ago?

the Cenozoic

How many genera of scleractinians survived into the Cenozoic after the extinction at the end of the Cretaceous period?

11

What was it like for reefs during the Cenozoic?

they struggled for a while on a greenhouse earth

What period do we eventually see reefs as we know them

cenozoic

What is the difference between aragonite and calcite?

calcium carbonate crystals come in several forms and different levels of magnesium leads to either calcite or aragonite

What does low magnesium lead to?

calcite

What does high magnesium lead to?

aragonite

Which is stronger but less stable?

aragonite

what type of skeletons do modern corals build?

aragonite

what types of skeletons do mollusks tend to build?

calcite

What causes one crystal to be favored over another?

ocean chemistry

What do icehouse seas favor?

aragonite

what do greenhouse seas favor?

calcite

What happens are the ocean warms?

calcite is favored

why does volcanism favor calcite

because it eats up magnesium and with less magnesium you have calcite

What changes with the environmental fluctuations of greenhouse-icehouse and calcite versus aragonite?

the winning reef builders shift