#paleoclimate

Hello everyone! Did you miss me? Field season was wild but now I'm back and ready to talk more about rocks and fossils!

The Cambrian Explosion happened when marine life radiated rapidly into most of the basic body forms that we observe in modern groups today.

What made the Cambrian Period the ideal time and place for such an evolutionary burst? To get the answers, we need to go back in time just before the Paleozoic Era began.

Welcome to the Ediacaran Period, 600 million years ago. All of the continents were joined together to the form the supercontinent...Pannotia. You thought I was going to say Pangea, didn't you?

Pangea came much later. Pannotia sat on the south pole and it had a pretty massive ice cap on it. Of course, that was nothing compared to the snowball Earth o the previous period. The oceans were much cooler in this time and just like cold oceans today, it could have been the ideal breeding ground for plankton as cold water brings nutrients to the surface.

As the Ediacaran came to an end and the Cambrian began, the ice cap melted, the seas warmed up and the Pannotia began to break up.

One large continent, Gondwana, stayed at the south pole but several island continents moved toward the equator. The placements of the continents was critical to the evolutionary explosion.

Ocean currents have a huge impact on climate. If we look at this map of the Cambrian world and its ocean currents, you can see the cold currents at the mid-latitudes and poles heading to the equator where they warm up and go back to the poles to cool down.

Now, if I plug in all our important Cambrian fossil sites you'll see that a vast majority fall on or very near the equator. An increase in warm ocean water and a rise in oxygen brought on by melting ice were probably two big parts in the rise of living organisms. Cold water brings nutrients up and is circulated by ocean currents. Warm water facilitates the production of carbonates like limestone and calcite for living things like echinoderms and arthropods.

New research has uncovered that pollen preserved in 250 million year old rocks contain compounds that function like sunscreen, these are produced by plants to protect them from harmful ultraviolet (UV-B) radiation. The findings suggests that a pulse of UV-B played an important part in the end Permian mass extinction event.

Scientists from the University of Nottingham, China, Germany and the U.K. led by Professor Liu Feng from Nanjing Institute of Geology and Paleontology have developed a new method to detect plant's sunscreen-like compounds in fossil pollen grains. The research has been published today in Science Advances.

The end-Permian mass extinction event (250 million years ago) is the most severe of the big five mass extinction events with the loss of ~80% of marine and terrestrial species. This catastrophic loss of biodiversity was a response to a palaeoclimate emergency triggered by the emplacement of a continental-scale volcanic eruption that covers much of modern-day Siberia.

The volcanic activity drove the release of massive amounts of carbon that had been locked up in Earth's interior into the atmosphere, generating large-scale greenhouse warming. Accompanying this global warming event was a collapse in the Earth's ozone layer. Support for this theory comes from the abundant occurrence of malformed spores and pollen grains that testify to an influx of mutagenic UV irradiation.

Scientists:

Since the mid-19th century, global warming has climbed about 1 degree Celsius (1.8 degrees Fahrenheit), suggesting that the global average temperature of the last decade (2010-2019) was warmer than any time during the past 12,000 years. 

Shifting tectonic plates, not atmospheric carbon dioxide levels, controlled the strength of the powerful East Asian monsoon throughout its history, scientists say.

The monsoon is a seasonal system of winds that brings heavy rains to a vast swath of Asia, from India to Taiwan, each summer. The rains are a vitally important source of water for agriculture. Some previous research has suggested that past eras known to have had high atmospheric CO₂ levels and warmer temperatures might also have been times of fluctuating monsoon intensity. The implication that monsoons are far more sensitive to climate change than once thought is alarming in a warming world: Dramatic change in monsoon intensity in the near future would threaten food security for over a billion people.

Yet the new study offers some potentially good news on that front: Even during very warm periods in Earth’s past, such as the Eocene Epoch that lasted from 56 million to 34 million years ago, the monsoon’s intensity wasn’t much different than it is today.

Alexander Farnsworth, a paleoclimatologist at the University of Bristol in England, and colleagues combined plate tectonic reconstructions with paleotemperature “proxies” that provide clues to past climatic conditions. Such proxies, found in and near the Tibetan Plateau, include ancient fossils and pollen, as well as sedimentary deposits. Using these data, the team reconstructed the evolution of the monsoon going back 150 million years. What really exerted control over changes in the monsoon’s intensity were Earth’s slowly but constantly shifting landmasses, the team reports October 30 in Science Advances.

In China’s Yunnan Province, which includes part of the Tibetan Plateau, scientists collect sediment samples and leaf fossils dating to between 34 million and 23 million years ago. Such samples help reconstruct the ancient environment — and therefore, can reveal changes in monsoon intensity through time.

CREDIT: A. FARNSWORTH

The study also suggests that the monsoon is far older than once thought. “The traditional model is that the monsoon itself has only existed for the last 23 million years,” Farnsworth says. But new plant fossil data from the region have suggested that at least parts of the Tibetan Plateau were very wet much further back in time (SN: 3/11/19).Monsoon conditions existed as far back as the Early Cretaceous Period, about 136 million years ago, the study finds. But by 120 million years ago, the monsoon was gone, and for the rest of the Cretaceous, East Asia remained arid. Then, around 60 million years ago, the monsoon reappeared and began to intensify over the next 20 million years. It remained strong and stable until about 13 million years ago, when it kicked into high gear — a time that the scientists call the mid-Miocene “super-monsoon.” About 3.5 million years ago, it weakened again to an intensity similar to today’s.

Visually seeing natural climate cycles vs. human-induced climate change: This is an 800,000-year record of atmospheric carbon dioxide (CO2) concentrations (in parts per million, or ppm) from Antarctic Ice Cores (scientists analyze gases trapped in air bubbles in the ice). This data can be found at the NOAA Paleoclimate Database.

650 million years ago, Earth was covered in ice during an "extreme" 15-million-year-long ice age. New research suggests that towards the end this period, Earth may not have been fully frozen, however. The findings suggest the planet was more "slushball Earth" than "Snowball Earth," with patches of open water existing in shallow mid-latitude seas. This slushball state could have actually helped life survive during this extreme glacial period on our planet.

Researchers made the discovery when studying samples from the eastern Shennongjia Forestry District of China's Hubei Province which dates back to the glacial period called the Marinoan glaciation, theorized to have ended between 628 million and 623 million years ago.

The Marinoan glaciation is is considered one of the most extreme ice ages Earth has experienced. "We called this ice age 'Snowball Earth. We believed that Earth had frozen over entirely during this long ice age," University of Cincinnati professor of geosciences, Thomas Algeo, said in a statement. "But maybe it was more of a 'Slushball Earth.'"