Tag Archives: volcanoes

Amborella Day

205-193 million years ago

1 galactic revolution ago

The Triassic ends 201 million years ago with another major mass extinction (the fourth, by the usual count, after the end-Ordovician, end-Devonian, and end-Permian). Not quite as bad as the end-Permian (“only” 75% of species go extinct). This coincides with the formation of the Central Atlantic LIP (Large Igneous Province), which now includes a lot of eastern North America, northeast Amazonia, and western North Africa. So the end Triassic mass extinction may be the result of volcanoes spewing lava and carbon dioxide as Pangaea splits into Laurasia (North America, most of Eurasia) and Gondwanaland (South America, Africa, Antarctica, India, Australia).

The succeeding Jurassic Period will be when dinosaurs become the dominant vertebrates on land. The mammals around are mostly shrew-sized and nocturnal.

Not as conspicuous is another evolutionary innovation: the ancestors of Amborella, a rare shrub found in the wild only on New Caledonia, split off from the other angiosperms, ancestors of all other flowering plants, 200 million years ago. (This was suspected for a while, and confirmed in 2012 with the sequencing of the Amborella genome.) We can call this the origin of flowers. Amborella has clusters of small white flowers, with male and female separate.

amborella

People expect to get flowers on Mother’s Day and Valentine’s Day, but not on March 17. But Spring is gearing up in the Northern hemisphere. (The apricot tree in my back yard is in full bloom.) So surprise someone with flowers for Amborella Day!

The worst of times

260 million years ago: the Capitanian mass extinction

A capsule summary of the evolution of life on Earth goes like this: There is steady progress in adaptation, driven especially by arms races, sometimes involving competitors, sometimes predators and prey. But this progress is interrupted from time to time by catastrophes – mass extinctions resulting from extrinsic causes, sometimes astronomical, but more often geological. (We’ll see much later in the year that a similar summary of human history goes like this: steady progress in the scale of cooperation driven by arms races, with occasional catastrophic interruptions, often associated with the spread of epidemic diseases.)

The geological causes of mass extinctions have been coming into focus lately. Many mass extinctions co-occur with the formation of Large Igneous Provinces (LIPS), regions where vast amounts of lava have flowed out of the earth, triggering a whole cascade of changes: the destruction of the ozone layer by halogen gases, global warming induced by CO2 and methane, and anoxic seas.

The mass extinction 260 million years ago, the Capitanian, is not one of the classic five greatest mass extinctions, and has been overshadowed by the mother of all mass extinctions, the end-Permian, which happened just 8 million years later. But it took a major toll on living things, from marine organisms to dinocephalians. (The dinocephalians – more closely related to mammals than to dinosaurs, ranging up to hippo sized, and including both herbivores and carnivores – went entirely extinct with the Capitanian.) The Capitanian extinctions coincide with, and were probably caused by, the formation of Emeishan LIP, now in southwest China.

dinocephalians

A book published recently, The Worst of Times, pulls together the latest evidence that the Capitanian was the beginning of an 80 million year period in which mass extinctions were exceptionally common. Apparently the formation of the supercontinent of Pangaea and the Panthalassic superocean made living things particularly vulnerable to volcanically induced extinctions. Once Pangaea breaks up, mass extinctions are less frequent, and generally have different causes.  The death of the dinosaurs had an extra-terrestrial cause, and the mass extinction we’re in the middle of results from the activities of one very unusual species.

pangaea

My name is LUCA. I live on the ocean floor.

How life began on Earth is still not well understood. The “RNA world” is one popular theory. In modern organisms, nucleic acids, DNA and RNA, store and transfer information, but proteins do the actual work of catalyzing chemical reactions. But RNA can act as a catalyst, so maybe the first replicating systems involved RNA catalyzing its own replication. However, RNA doesn’t spontaneously form very easily, so it’s not clear how the RNA world would have gotten started. Borate minerals might help but it’s not clear they were around that early.

Another possibility that’s gotten some attention lately involves droplets that grow and divide, instead of just merging into bigger drops.

A different approach to the topic is to work backward from living organisms, to reconstruct the biochemistry of LUCA, the Last Universal Common Ancestor (not quite the same as the first living thing). Recent research on these lines implies that LUCA was a heat-loving microbe that relied on hydrogen as its energy source, suggesting an undersea volcano as a habitat.

However the first organisms got established on Earth, it happened very quickly. Just about as soon as the planet could support life we find chemical evidence for it, from Isua, Greenland (but no fossils yet). This suggests that the origin of life is pretty easy (unless we want to go with panspermia). Mars may have been a more habitable place early in its history, and perhaps Mars exploration will one day solve the mystery of the origin of life in our Solar System.

Exodus

1628 BCE, and later. There are two great stories in the Western tradition that stand somewhere between legend and history: The Flight from Egypt and the Trojan War. Both have been scholarly battlegrounds, dismissed as pure invention by some, accepted as at least partly historical by others. In the case of the exodus story, a great many archeologists nowadays are strong skeptics. Here I’ll summarize what I think is the best argument for the other side.

Barbara Sivertsen, in her book The Parting of the Sea, argues that the exodus story combines oral traditions arising from two different flights from Egypt. First, she suggests that some of the story reflects events around the time of a huge volcanic explosion, the largest in the last five thousand years, which destroyed most of the island of Thera (= Santorini) in 1628 BCE. Most of the Biblical plagues fit what would have been expected in northern Egypt at the time. A tsunami reaching the Nile delta would have contaminated water, and caused fish to die off. Frogs would have been driven from the water. Caustic ash would have stung human skin (in later recountings, “stinging like gnats” was remembered as “stinging gnats”). Insects affected by ash would have sought shelter in people’s houses. Livestock outdoors would have died from breathing ash, and humans and livestock would have developed blisters. Eventually dust in the atmosphere would have precipitated hailstorms. The arrival of the heaviest part of the dust cloud would have shrouded the land in darkness. (Locusts, however, don’t fit the volcano story, and may be an embellishment or a coincidental plague.) All these developments would have precipitated a panicked flight from Egypt on the part of Israelites, led by Moses. According to the archeological evidence, the Wadi Tumilat, an oasis/caravanserai east of the Nile commonly identified as the Biblical Land of Goshen, is abandoned at this time and left uninhabited for centuries.

Other authors have suggested that the Thera eruption had some role in the exodus, but Sivertsen thinks there was also a later flight. In the mid-1400s, Egypt had a significant population of prisoners of war employed as slaves at Tell el-Da’ba, a naval base on the Mediterranean. In Sivertsen’s account, a wave of deaths of Egyptian children led Pharaoh Tuthmose III, frightened of the Israelite god, to expel a group of Israelite slaves. The pharaoh changed his mind, however, and sent an army in pursuit of the slaves along the northern shore of the Sinai. We know that in the mid-1400s, another volcanic eruption, on the Aegean island of Yalli, sent a tsunami around the shores of the eastern Mediterranean. This tsumani caught up with the Egyptian army, but missed Israelites camped further inland. The event was spectacular enough to be melded with the earlier exodus story.

A major reason for skepticism about the exodus story is that it has been very hard to find evidence for the Israelite conquest of Canaan in the fourteenth or thirteenth century BCE, which is when many accounts place the exodus. But if we follow Sivertsen in putting the first exodus much earlier, and allow that the “forty years” in the wilderness was really eighty years, then there is plenty of evidence for massive invasion and destruction of cities in Canaan in the mid 1500s, at the end of the Middle Bronze Age. Israelites could have been among the invaders of Canaan. Around 1550 BCE, the city of Jericho suffered an earthquake that knocked down some of the city walls. The city then burned to the ground, and was largely abandoned subsequently.

We saw earlier on Logarithmic History that oral history can preserve detailed memories of natural catastrophes for long periods of time. At the same time information about numbers and absolute dates mostly gets lost. It will be interesting to see how Sivertsen’s work holds up in the face of further discoveries.

Toba? or the sperm whale effect?

74 thousand years ago, a big chunk of the island of Sumatra blew up. It was the biggest volcanic explosion in the past two million years, expelling 2800 times as much debris as the Mount Saint Helens eruption in Washington State in 1980. Ash from the super-eruption is found all the way from Lake Malawi to the South China Sea. The resulting Toba caldera measures about 20 by 60 miles.

toba

The Toba eruption coincides with a shift back to glacial conditions, and it may be that there’s a connection, that Earth went through a long volcanic winter after the eruption, which shifted climate to a colder equilibrium.

Did Toba have an effect on human evolution? Somewhere between 100 and 50 thousand years ago, human populations went through a bottleneck: modern humans are descended from just 1,000 to 10,000 breeding pairs from that period. It’s been argued that Toba wiped out the majority of Homo sapiens around at the time, leaving only a small group of survivors.

But the evidence that Toba is responsible for the bottleneck is equivocal. In some places humans seem to have passed through the period of the eruption without major disruptions. Also, there’s a point that gets missed in a lot of popular reporting: just because a species went through a bottleneck doesn’t necessarily mean that the population of the whole species ever shrank to that size. In the case of Homo sapiens it could be that the total population was always many times larger than 1,000-10,000. It’s just that the other tens or hundreds of thousands got replaced. In other words, we may not be looking at an external catastrophe wiping out most of humanity, and a few groups of survivors recovering. Instead, we may be looking at a small population of our eventual ancestors expanding and outcompeting other populations, so that it was our ancestors, not a volcano, who made sure that most human beings alive 74,000 years ago didn’t leave descendants.

This may reflect something special about human evolution: human beings typically belong to tribes and ethnic groups defined by distinctive cultures, and cultural boundaries (including language boundaries) often act as barriers to interbreeding. Several authors have suggested that this may make human beings unusually susceptible to population replacement via “cultural group selection,” and that this might account for humans having unusually low effective population size, as genes “hitchhike” along with expanding cultures. Interestingly, sperm whales, which live in populations defined by different song dialects (and other cultural differences) may show the same genetic pattern.

In May 2015, the Toba volcano grew more active than usual, producing large emissions of steam and foul gases. Locals were reported to be concerned.

The worst of times

260 million years ago: the Capitanian mass extinction

A capsule summary of the evolution of life on Earth goes like this: There is steady progress in adaptation, driven especially by arms races, sometimes involving competitors, sometimes predators and prey. But this progress is interrupted from time to time by catastrophes – mass extinctions resulting from extrinsic causes, sometimes astronomical, but more often geological. (We’ll see much later in the year that a similar summary of human history goes like this: steady progress in the scale of cooperation driven by arms races, with occasional catastrophic interruptions, often associated with the spread of epidemic diseases.)

The geological causes of mass extinctions have been coming into focus lately. Many mass extinctions co-occur with the formation of Large Igneous Provinces (LIPS), regions where vast amounts of lava have flowed out of the earth, triggering a whole cascade of changes: the destruction of the ozone layer by halogen gases, global warming induced by CO2 and methane, and anoxic seas.

The mass extinction 260 million years ago, the Capitanian, is not one of the classic five greatest mass extinctions, and has been overshadowed by the mother of all mass extinctions, the end-Permian, which happened just 8 million years later. But it took a major toll on living things, from marine organisms to dinocephalians. (The dinocephalians – more closely related to mammals than to dinosaurs, ranging up to hippo sized, and including both herbivores and carnivores – went entirely extinct with the Capitanian.) The Capitanian extinctions coincide with, and were probably caused by, the formation of Emeishan LIP, now in southwest China.

dinocephalians

A book published last year, The Worst of Times, pulls together the latest evidence that the Capitanian was the beginning of an 80 million year period in which mass extinctions were exceptionally common. Apparently the formation of the supercontinent of Pangaea and the Panthalassic superocean made living things particularly vulnerable to volcanically induced extinctions. Mass extinctions still happen, but not as frequently, once Pangaea breaks up.

pangaea

Toba

74 thousand years ago, a big chunk of the island of Sumatra blew up. It was the biggest volcanic explosion in the past two million years, expelling 2800 times as much debris as the Mount Saint Helens eruption in Washington State in 1980. Ash from the super-eruption is found all the way from Lake Malawi to the South China Sea. The resulting Toba caldera measures about 20 by 60 miles.
 
toba

The Toba eruption coincides with a shift back to glacial conditions, and it has been argued that there’s a connection, that Earth went through a long volcanic winter after the eruption, which shifted climate to a colder equilibrium.

Did Toba have an effect on human evolution? Somewhere between 100 and 50 thousand years ago, human populations went through a bottleneck: modern humans are descended from just 1,000 to 10,000 breeding pairs from that period. It’s been argued that Toba wiped out the majority of Homo sapiens around at the time, leaving only a small group of survivors.

But the evidence that Toba is responsible for the bottleneck is equivocal. In some places humans seem to have passed through the period of the eruption without major disruptions. Also, there’s a point that gets missed in a lot of popular reporting: just because a species goes through a bottleneck doesn’t necessarily mean that the population of the whole species ever shrank to that size. In the case of Homo sapiens it could be that the total population was always many times larger than 10,000. It’s just that the others tens or hundreds of thousands got replaced. In other words, we may not be looking at an external catastrophe wiping out most of humanity, and a few groups of survivors recovering. Instead, we may be looking at a small population of our eventual ancestors expanding and outcompeting other populations, so that it was our ancestors, not a volcano, who made sure that most human beings alive 70,000 years ago didn’t leave descendants. We will see later on in Logarithmic History that population replacements have been a common occurrence in human history.

In May 2015, the Toba volcano grew more active than usual, producing large emissions of steam and foul gases. Locals were reported to be concerned.