Category: Paleontology

Extinctions and Space

There’s one sure way to spice up science headlines: add dinosaurs—and when you combine dinosaurs with space and exotic cosmology, you can’t go wrong.

Thirty years ago, a scientific hypothesis brought space and extinction together. Scientists noticed what appeared to be a regular repeating pattern of massive extinction events in Earth’s history, falling roughly every 26 million years. What could explain such a pattern? One possibility is that the cause lies in the ecosystems themselves: something about biological communities causes them to fail when they reach certain milestones. Another possibility is that the cause is external, resulting either from the geological processes of the Earth, or perhaps from something extraterrestrial.

Perhaps the most famous (though not the most severe) extinction event in history is the one that occurred at the end of the Cretaceous period and brought about the end of the dinosaurs; the evidence is now conclusive that a major meteor, asteroid, or comet impact near the present Yucatan played a decisive role in this extinction event. But if an impact event caused at least one major extinction event, could impacts be a more general cause of extinctions? Other evidence seemed to show, in addition to periodicity in extinctions, a similar periodicity of around 30 million years or so in the rate of impacts on the Earth’s surface. We thus have two pieces of evidence that fit together: extraterrestrial impacts and extinctions both occurring at similar intervals, the former being an obvious potential cause of the latter.

But what could cause impacts from space to occur in a regular pattern?

Periodicity is not uncommon in astronomy, and there’s an obvious source: orbits. Objects that travel in orbits around other objects naturally tend to display regular, periodic behavior. This line of thinking led to the proposal that it was in fact orbital motion that led to the regular peppering of Earth with extraterrestrial objects.

Far out beyond the orbit of the most distant planets lies the Oort cloud, a vast spherical region surrounding our Sun that is populated by icy bodies that, when they fall near the Sun, form comets. When the early solar system formed, the massive planets carved out a relatively clear bubble inside of which the Earth and the familiar planets orbit. The remaining debris ended up in one of three places: either sucked into the Sun or the forming planets, shepherded into the asteroid or Kuiper belts, or flung into the deep space of the Oort cloud. Every now and again, one of these Oort cloud objects comes falling into the inner solar system, appearing in our skies as a comet, but generally these bodies orbit slowly in the distant reaches, uninclined to make their way inwards.

Unless, that is, a gravitational tug upsets them, casting them in and out in showers of cosmic debris. This sort of gravitational tug can be given, for example, by a passing star—and it was just this realization that led, in 1984, to the suggestion that our Sun was not alone.

Instead, it was proposed that the Sun (like most stars in the galaxy) had a companion, a dim and distant dwarf (dubbed “Nemesis”) that followed in a wide orbit. Every thirty million years or so, Nemesis swung close enough in to the Oort cloud to scatter comets about, sending some of them inward on paths that would inevitably lead at least a few to impact the Earth. Thus, we find a pattern to impacts and, subsequently, extinctions on Earth.

In the years that followed, however, the Nemesis hypothesis foundered on the fact that no trace of the hypothetical star was found by any observations. The latest evidence supports the non-existence of Nemesis. A thorough examination of data from the WISE (Wide-field Infrared Survey Explorer) spacecraft, published just recently, found no bodies of significance out to 10,000 AU, and no signs of larger bodies at farther distances have been forthcoming. Nemesis was proposed as speculation, and a quarter century of observation has led to no observational support. The Sun, as far as we can tell, is alone, and no large planets or dwarf stars lurk beyond Neptune that could explain disturbances of the outer solar system that could lead to periodic comet showers.

***

But that doesn’t leave us bereft of hypotheses. The newest idea to explain periodic comet showers has to do not with large bodies disturbing the Oort cloud with gravity, but rather with the motion of the entire solar system itself. What’s more, the newest iteration of this latest hypothesis invokes one of the hot topics of modern astrophysics, dark matter.

milky-way-galaxy_nature.jpg

Just as the planets of the solar system orbit the Sun, the Sun itself orbits the center of the Milky Way galaxy, making a giant circuit that takes hundreds of millions of years to complete. But unlike the fairly flat orbits of the planets, the Sun’s orbit is wavy, coasting up and down through the plane of the galaxy. The reason for these waves is that the galaxy’s disk contains a significant amount of mass: as the Sun drifts upwards, the galaxy’s mass pulls it back down, until it plunges through the disk and emerges on the other side, drifting away until gravity pulls it back, repeating the process over again.

As it turns out, the period of this motion above and below the galactic plane appears to be about seventy million years, meaning that the solar system passes through the galactic plane about every—you guessed it—thirty-five million years or so, notably close to the purported period of increased impacts and extinctions. That period alone is enough to be suspicious; it may very well be that the ordinary gravitational disturbance of passing through the plane alone is enough to upset the distant solar system. The newest examination of the theory, however, invokes the latest speculative physics. Dark matter is a proposed form of matter that makes up the bulk of the universe and that interacts with normal matter in ordinarily negligible ways; there is no known means of detecting dark matter directly, but it is invoked to explain a number of observations that cannot be explained by normal matter alone.

Suppose, then, a new paper asks, that not only does the galactic disk contain a high concentration of normal matter, but it might contain disks of dark matter as well, and as the solar system plunges through these disks on its rising and falling track around the galaxy, it is this dense dark matter that causes icy comets to be scattered and sent to collide with the Earth.

Perhaps. Or perhaps motion through the galaxy alone is enough, even without dark matter, to account for the solar system’s disturbance. Or, it could be that we’re chasing phantoms—the statistical detection of impact periodicity and extinction patterns is weak: maybe there really is no periodicity to be explained. As always in science, time will give us more to consider.

_____

Image: Nature/C. Carreau-ESA

Reconsidering the “Great Oxidation Event”

Earth’s early atmosphere containedEarth with auroras (NASA) very little oxygen. The rise of photosynthetic organisms, which produce oxygen as a byproduct, led to increasing levels of oxygen in the atmosphere, and later the appearance of nonphotosynthetic organisms (like us) which used oxygen as an ingredient in energy-prducing cellular respiration.

A new study suggest that the oxidation of the Earth’s atomsphere was a longer and more variable process than previously thought:

‘The evidence for the Great Oxidation Event has mainly come from the sudden disappearance in the record of a particular chemical signature of volcanic sulfur that signals the removal of a major oxygen ‘sink’, and the permanent accumulation of oxygen in the atmosphere.

But, in a new review of the latest scientific literature, Lyons and colleagues argue that relying on this record alone has been misleading.

“A big message of this paper is that the Great Oxidation Event is really a very protracted and dynamic transition rather than a single step,” says Lyon. “We suggest it shouldn’t be called an event at all.”

Lyons and colleagues argue photosynthesis probably started earlier around 3 billion years ago but the oxygen it produced was largely removed from the atmosphere by tectonic processes that led to emission of reducing sulfur, hydrogen and methane gases.

Such processes led to a much more complicated rise and fall of oxygen levels over Earth’s history than previously thought, says Lyons.

“There’s a dance between production and consumption of oxygen with huge implications for life on Earth.”

“The oxygen curve was not just low, intermediate and high, which is what has been in everyone’s mind forever.”‘

Read here (ABC Science).

_____

Image: NASA

Dinofuzz

 

"Dinofuzz" in amber (Science/AAAS)

Science reports:

“Fluffy structures trapped in thumbnail-sized bits of ancient amber may represent some of the earliest evolutionary experiments leading to feathers, according to a new study. These filaments of “dinofuzz” are so well preserved that they even provide hints of color, the researchers say.

The oldest bird, Archaeopteryx, lived in what is now Germany about 150 million years ago, and the oldest known feathered dinosaur, Anchiornis huxleyi, lived in northeastern China between 151 million and 161 million years ago. Both creatures had modern-style feathers, each of which had a central shaft; barbs, which made up the feather’s vane; and substructures called barbules tipped with Velcro-like hooklets that held the barbs together to form a sturdy aerodynamic surface.

Structures believed to represent earlier stages of feather evolution, such as flexible, unbranched filaments—often called protofeathers but sometimes dubbed “dinofuzz”—have been found in fossils of dinosaurs that lived long after Archaeopteyrx and Anchiornis but had not been discerned in older fossils.

When Ryan McKellar, a paleontologist at the University of Alberta in Canada, and his colleagues searched through more than 4000 bits of amber in Canadian museum collections, they found 11 specimens that included remnants of feathers and protofeathers. The largely transparent chunks of amber—most of them smaller than 1 centimeter across—had been pulled from coal deposits laid down about 78 million or 79 million years ago, when the region, then near sea level, was a wetland covered with conifer forests.

Upon closer inspection, McKellar and his team noticed that some of the feathers resemble those found on modern birds, complete with barbs sporting tiny Velcro-like hooks that lock onto adjacent barbs to create a sturdy flight surface. Some of these fragments likely came from a flight-capable bird. Others contained structures that helped the feathers absorb water, similar to those found on modern-day waterfowl, which use water-soaked feathers to counteract their buoyancy when they dive beneath the surface to chase prey or to forage on a lake bottom. These feathers possibly came from an ancient waterfowl similar to modern-day grebes, the researchers suggest.”

Read here.

Getting Older

…Life and Man may be, that is.

The first story here is from the University of Oregon, where geologists claim to have identified land-dwelling fossils from 2.2 billion years ago, four times older than the generally accepted date of the first land life. From the university:

A new study, led by geologist Gregory J. RetallUniv. of Oregonack of the University of Oregon, now has presented evidence for life on land that is four times as old — at 2.2 billion years ago and almost half way back to the inception of the planet.

That evidence, which is detailed in the September issue of the journal Precambrian Research, involves fossils the size of match heads and connected into bunches by threads in the surface of an ancient soil from South Africa. They have been named Diskagma buttonii, meaning “disc-shaped fragments of Andy Button,” but it is unsure what the fossils were, the authors say.

“They certainly were not plants or animals, but something rather more simple,” said Retallack, professor of geological sciences and co-director of paleontological collections at the UO’s Museum of Natural and Cultural History. The fossils, he added, most resemble modern soil organisms called Geosiphon, a fungus with a central cavity filled with symbiotic cyanobacteria.

This is not the first time that Retallack has argued for earlier land life, and with its vastly older age the new claim will certainly not be one that is accepted uncritically.

***

Elsewhere, genetics has revealed something interesting: the discovery of a new Y-chromosome lineage. Y-chromosomes are passed down through male generations, preserved from the sort of mixing that happens to the other chromosomes. They can thus be used to identify clear lineages, much like mitochondrial DNA can be used to establish matrilineal lineages. Geneticists have previously been able to trace the Y-chromosome lineage back to about 200,000 years ago to a hypothetical figure called “Y-chromosome Adam” who would represent the individual from whom all modern humans have inherited their Y-chromosomal DNA (although not the only human living at that time, or the only human to contribute to all modern human DNA.) Now, however, something new has turned up.

RealClearScience reports:

The DNA of Albert Perry may change the story of human origins. Perry, an African-American, approached a DNA testing company to find out more about his ancestry. The results would have come as quite a surprise (had he lived to see them), and have raised questions for geneticists around the world.

It turns out that Perry carried a very different type of Y chromosome, never seen before. Every male has a Y chromosome, which is a piece of DNA inherited by sons from their fathers. But, unlike most DNA, the Y chromosome is not shuffled as it is passed down, and changes only slowly through mutation. Tracking these mutations allows scientists to create a genetic tree of fathers and sons going back through time.

As a man may have several sons or none, some branches of the genetic tree die out each generation, while others become more common. Going back through time it is therefore inevitable that all modern Y chromosomes must descend from from one man at some point in the past. He has become known as “Y-chromosomal Adam”.

This Adam was not the first man, or the only man, from his time to contribute to modern human DNA. It is just that, by chance, his Y chromosome was the only one to survive until today.

What is surprising about Perry’s Y chromosome is that it did not descend from Y-chromosomal Adam’s. Or rather that the established “Adam” has lost his title to a new “Adam”, further back in time, where Perry’s branch split from the tree (see figure). While the former-Adam is estimated to have lived around 202,000 years ago, the revised one is thought to be about 338,000 years old.

Read the story here.

 

North American Monkeys?

animals-monkeys35For an interesting weekend read, from Popular Science: Why are there no native monkeys in North America?

“Primates came to the New World (meaning North and South America) from, we think, Africa. As improbable as it sounds, scientists think early primates crossed the Atlantic Ocean and landed on the shores of both continents tens of millions of years ago, probably on some kind of vegetation raft. That’s how most plants and animals get to isolated islands–which the Americas were, at the time. Fossils have been recovered of early primates in Texas a whopping 43 million years ago, the oldest primate fossil ever found in North America. But the continents looked very different then, compared to now; most importantly, North and South America were completely different islands. The Isthmus of Panama, which we now refer to as Central America, didn’t appear until much later, by which time the climate on both Americas was very different from when the primates first landed there.”

Read here.

 

Monday Links

“The Saturn Propulsion System (1962)”

– The main engines from the Saturn V rocket that launched one of the Apollo missions to the moon have been recovered from the Atlantic Ocean, where they fell over 40 years ago;

– Brian Switek of Laelaps is disappointed that the newest Jurassic Park film will have scientifically inaccurate dinosaurs—they will be featherless;

– and, The Economist looks at what Chinese fossils may have to tell us about the Cambrian explosion.

 


Video: NASA/Jeff Quitney

Monday Links: Feser on Metaphysics, Lewis and Scientism, and Backwards Vertebrate Fossils

  • Edward Feser writes at his blog:

    “That secondary causes are true causes, even if ultimately dependent on God, is necessary if natural science is to be possible.  If occasionalism were true, absolutely everything that happens would, in effect, be comparable to a miracle and there would be no natural regularities to discover.  Physics, chemistry, biology, and the like would be nothing other than branches of theology — the study of different sorts of divine action rather than of (say) the properties of magnetism, electricity, gravitation, hydrogen, helium, bodily organs, or genetic material as such.  And if God’s ways are inscrutable (as they must be given that He is pure actuality, subsistent being itself, etc.), then there could in that case be little reason to expect regularity in any of these spheres.  (As Alain Besançon has argued, a tendency toward an occasionalist conception of divine causality is part of what distinguishes Islam from Christianity – and this is no doubt one reason why natural science progressed in the West and stagnated within the Islamic world.)”

  • And MercatorNet hosts an interview with John G. West on C. S. Lewis’ worries about scientism:

    “Finally, Lewis saw that science, like magic, can be a quest for power over nature and our fellow human beings. Many times that power will be used for good, but if modern science is cut off from traditional ethical norms, its power may be increasingly misused. During Lewis’s own lifetime, he saw the horrific results of the misuse of science in the eugenics movement and its effort to breed a master race by applying the principles of Darwinian biology.”

  • And finally, a new study suggests that reconstructions of early land-dwelling tetrapods might have the backbones backwards. This isn’t, of course, the first time this sort of thing has happened in paleontology.

Oldest Arthropods in Amber

The oldest amber-encased arthropods have been found in a sample of Triassic period amber, dating to about 230 million years ago. Amber is the fossilized remains of tree sap or resin, and in some cases amber contains insects or other matter trapped inside the amber when it was still liquid. Such instances provide very well preserved remains of ancient organisms.  Researchers screened around 70,000 tiny droplets of amber recovered from the Dolomite Alps in northern Italy and found three examples of two new species of gall mites. While modern gall mites feed predominantly on flowering plants, the researchers note that as these mites lived before the appearance of flowering plants, they must have fed on the common ferns and conifers of the Triassic period instead. These are the oldest arthropods yet found encased in amber, and the first example dating from the Triassic period.

The research is published in the Proceedings of the National Academy of Sciences: Schmidt et al. Arthropods in amber from the Triassic Period. PNAS. Published online before print August 27, 2012, doi: 10.1073/pnas.1208464109

(American Museum of Natural History)

Image: Am. Mus. Nat. Hist./PNAS

Oldest Southeast Asian Modern Human Fossil Found

Researchers have uncovered the oldest known modern human fossils from southeast Asia. The team discovered a fragmented human skull in a cave in the Annamite Mountains of Laos, and they have dated the fragments to between 46,000 and 63,000 years of age. University of Illinois anthropologist Laura Shackelford, leader of the team that found the skull, says, “It’s a particularly old modern human fossil and it’s also a particularly old modern human for that region. There are other modern human fossils in China or in Island Southeast Asia that may be around the same age but they either are not well dated or they do not show definitively modern human features. This skull is very well dated and shows very conclusive modern human features.”

The finding is about 30,000-50,000 years older than the next-oldest modern human fossils from the area, pushing the evidence for a human presence there further back in time. Shackleford says that the date also provides fossil evidence in support of genetic studies that place the human presence in southeast Asia back about 60,000 years.

The finding is reported in the Proceedings of the National Academy of Sciences.

(University of Illinois)

Image: University of Illinois/F. Demeter

The Beast in His Natural Habitat

by Andrew Ratelle

Beneath the scorching heat and wind of a Wyoming summer, a mix of nearly a hundred volunteers and hired hands worked some six thousand man hours between the months of June and July digging for treasure. Hidden within the same land that made cattle farmers rich and oil barons richer lay a find many times rarer, and to some, many times more precious than even the blackest gold.

A nearly complete backbone, fully articulated with the upswept arch of rigor mortis still preserved was found along with an intact pelvis, ribs, and thighbone. They belonged to a Tyrannosaurus rex, one not yet fully grown, but still large enough to have stretched at least fifteen feet from shoulders to hips.

Finds like this are uncommon enough, but more uncommon still is the manner of their preservation. The bones were encased within a sedimentary concretion, a single block of natural concrete made up of the mud and sand that filled in and around the corpse near the time of death and petrified along with the animal’s remains. It’s an exceptionally rare type of process that can produce a natural “mummification” of sorts, preserving any undecayed skin, tendons, muscle, and internal organs along with what’s left of the skeleton. Read more →