Showing posts with label fossils. Show all posts
Showing posts with label fossils. Show all posts

June 29 - Discovery of an Island Oxymoron

  Posted on June 29, 2022     


This is an update of my post published on June 29, 2011:



On this day in 1994, Dr. Tom Rockwell and his student Kevin Colson found the fossilized skull and shoulder blades of a pygmy mammoth sticking out the sand and rock on Santa Rosa Island, in California.

(The word pygmy means “small,” and of course mammoth means “large,” so the pygmy mammoth's name is an oxymoron—that is, a phrase that seems to contradict itself. Of course, mammoths were creatures in the elephant family; the various now-extinct mammoth species were quite hairy compared to modern elephants because they lived during the Ice Age and at higher latitudes than the equator-hugging lands where modern elephants live. The pygmy mammoth fossils discovered on a California island represents a kind of mammoth that is smaller than other mammoths.)


Pygmy mammoths compared in size to "regular
mammoths," above, and to a full grown human, below.




It turned out that the fossilized skeleton that Rockwell and Colson found was nearly complete. This is the only full-sized skeleton of this particular species found anywhere, and it is also the first to be dated—it's about 12,840 years old.

How do skeletons become fossils?

Most organisms rot away to nothing when they die. Very few become fossils—but so many creatures have lived in earth's loooong history, scientists have still managed to find billions of fossils, representing hundreds of thousands of different species.



Here's one way in which an organism can become fossilized:

  • An animal dies and falls to the bottom of a sea or lake.

  • Soft parts rot away, leaving the skeleton.

  • Dirt, sand, bits of rock and shell, and other sediment falls onto the skeleton and buries it.

  • As more sediment piles on, pressure increases on the lower layers, and they turn to hard rock.

  • The bones dissolve by ground water, leaving holes of the same shape, which act as molds.

  • Minerals crystallize inside the molds, creating fossils that are made of minerals but that have the same shape as the original bones.

  • Later (as in millions of years later), the rock is uplifted and exposed by erosion. The fossils are now exposed, waiting to be discovered.


Of course, some fossils are not mineralized bones (above)...
but rather impressions of shells or bones or even leaves or footprints (below)...




For a longer description of the process of fossilization, go here.




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May 13 - Remembering Georges Cuvier

    Posted on May 13, 2022

This is an update of my post published on May 13, 2011:




Georges Cuvier named the pterodactyl and the mosasaurus. He opposed the idea of evolution. He proved that species of animals have gone extinct. He believed that the “original people” were white (Caucasian). He established the fields of comparative anatomy and paleontology.


Like so many scientists who lived and worked a long time ago, Cuvier had some really good ideas that established or revolutionized branches of science—but he also had some ideas that, since his death, have been shown to be utterly wrong. 

(And racist!)

When you look at the work of Cuvier, a French biologist and paleontologist who died on this day in 1832, you can't help thinking - or at least hoping - that he would have changed many of his incorrect views if he could've seen the evidence we humans have gathered since his time.

For example, in opposing evolution—the idea that populations of animals change over time—Cuvier was opposing the theories of his contemporaries, Lamarck and Geoffroy Saint-Hilaire. And, we now know, those theories were incorrect. Charles Darwin's theories of common descent and of evolution driven by natural selection—which have been added to, now that we know about genes and DNA, and which TONS of evidence show are essentially correct—wouldn't be published until more than 20 years after Cuvier died.


Fossils drawn by Georges Cuvier

As the saying goes, in science we stand on the shoulders of giants. Today's average 11 year old kid knows more science than the most brilliant Ancient Greek natural philosopher, and a college freshman pre-med student knows more Bio, probably, than Cuvier! Still, Cuvier is one of those giants of intellect and endeavor upon whose work biology is built.


Cuvier believed in catastrophism...

Cuvier studied fossils of animals that no longer exist today, such as the wooly rhinoceros and the mammoth, and he came to believe that they went extinct due to some sort of natural catastrophe. Geologists who put forth the theory of catastrophism explained geological formations through catastrophes, too; for example, the carving of canyons and valleys might be explained by mighty floods.

The opposite of catastrophism is uniformitarianism. This is the theory that geological features can be explained by forces we can see today, acting gradually over years, decades, centuries, millennia. Under this theory, valleys and canyons (for example) are carved slowly and gradually by the slow movement of glaciers, or by many rainstorms and erosion events.


Glaciers carve U-shaped valleys.
Rivers tend to carve V-shaped valleys,
but of course over the course of time,
many of these valleys widen.




 
Today geology is based on uniformitarianism and catastrophism, together. Earthquakes and volcanoes seem like natural catastrophes to us, but to a geologist, these and other tectonic forces are constant enough to be an important, almost continuous, part of land formation and shaping. Erosion tends to be almost continuous, too. Catastrophes such as super-volcanoes, major storms and floods, and of course huge meteors (perhaps asteroids or comets) that impact the Earth all happen occasionally and sculpt the land as well. 

Biologists and geologists have worked out together that (almost certainly) at least some animal extinctions have been caused by huge tectonic or impact events. (And of course, extinctions of some species of plants and other organisms would share these same causes.)




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November 23 - Dinosaur-Era Fossils Found in Antarctica

 Posted on November 23, 2021


This is an update of my post published on November 23, 2010:



Antarctica is continent covered by ice about a mile thick. Despite the fact that the oceans surrounding the continent team with life—penguins and seals, giant squid and whales, its frozen interior lands are almost lifeless.


But it wasn't always so!

On this day in 1969, a team of paleontologists discovered the fossilized bones of Lystrosaurus, a therapsid reptile (these are the ancestors of modern mammals) that lived 200 million years ago. It was a creature that lived in warm climates.



Whaaat?

Remains of Lystrosaurus had earlier been found in southern Africa and Asia, so the new finding of Antarctic dinosaurs proved that the three continents had once been joined in a super-continent we call Gondwana. The portion of this supercontinent that is now Antarctica was located straddling the equator, which explains its mild temperatures, but when Godwanna broke up millions of years ago, and the various chunks of land drifted about, Antarctica drifted to the polar location we see today.


Before there was Gondwana - plus another supercontinent called Laurasia - 
there was Pangea, one huge all-the-world's-lands-in-one-super-continent. 



The theory that continents have drift around on the surface of the Earth is called, naturally, continental drift. Alfred Wegner first proposed continental drift in 1912, and most scientists were skeptical of the idea. However, evidence from the geographical shape and geological content of the continents, tectonic forces in the Atlantic Ocean (which even today is getting measurably wider as the ocean-floor plates pull away from each other), plants and animals, and fossil remains, data on the flip-flop of the planet's magnetic poles—all of that evidence has shown Wegner's idea to be correct. Also, geologists have come up with a mechanism to explain how continents can move around: plate tectonics.

Did you know...?


Way back in the 1700s, Benjamin Franklin noticed that Africa and South America seem to fit together like jigsaw puzzle pieces, and he suggested that they were once connected. Of course, unlike Wegner, Franklin did not collect comparative data to try to prove the point.

The Earth's magnetic field has “flip-flopped” many times in the past, with North becoming South and vice versa. This field reversal doesn't happen overnight, but instead takes thousands of years. And it may be that it is about to flip soon! Apparently the North-South switcheroo happens once every 250,000 years, give or take a few hundred years—but it has been 750,000 years since the last pole reversal! We are loooong overdue! Also, right now Earth's magnetic field is lessening year after year—and it is believed that this is a first sign of an oncoming magnetic field flip.

Find out more...


Here is a video that shows continental drift from 200 miliion years ago until now.

Did you know that the continents are STILL drifting? Here's what one of the possible ways the Earth could change in the next 250 million years! But there are various theories about  where the continents are heading:


Older students might like to complete a lesson on the fossils of Antarctica. There are links to several interesting websites/articles here.


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