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The Geologic Time Spiral

January 10, 2016

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The Geologic Time Spiral
A Path to the Past
Designed by Joseph Graham, William Newman, and John Stacy

The Earth is very old—4.5 billion years or more according to scientific estimates. Most of the evidence for an ancient Earth is contained in the rocks that form the Earth’s crust. The rock layers themselves—like pages in a long and complicated history—record the events of the past, and buried within them are the remains of life—the plants and animals that evolved from organic structures that existed 3 billion years ago.

Also contained in rocks once molten are radioactive elements whose isotopes provide Earth with an atomic clock. Within these rocks, “parent” isotopes decay at a predictable rate to form “daughter” isotopes. By determining the relative amounts of parent and daughter isotopes, the age of these rocks can be calculated.

Thus, the scientific evidence from rock layers, from fossils, and from the ages of rocks as measured by atomic clocks attests to a very old Earth.

See USGS Fact Sheet 2007-3015 at http://pubs.usgs.gov/fs/2007/3015/ for ages of geologic time periods. Ages in the spiral have been rounded from the age estimates in the Fact Sheet. B.Y., billion years; M.Y., million years. For more information, see the booklet on Geologic Time at http://pubs.usgs.gov/gip/geotime/.

The Geologic Time Spiral poster is available for purchase from the USGS Store: http://store.usgs.gov/b2c_usgs/b2c/start/%28xcm=r3standardpitrex_prd%29/.do

Thank you, Skeen!

Taurid fireballs

November 2, 2015

mchelsmusings cool, Science is Awesome Taurid fireballs, The South and North Taurid meteor showers 2 Comments

EarthSky – Release Date: Nov 02, 2015

We’ve been hearing reports of Taurid fireballs! It’s time to start watching for them. Details on the South Taurid shower, and when to watch.

Taurid fireball caught in bright moonlight in Tucson, Arizona.

Taurid fireball caught in bright moonlight by Eliot Herman in Tucson, Arizona. Photo taken at 3-38 a.m. on November 1, 2015

The South and North Taurid meteor showers aren’t known for their large numbers of meteors, but they are known for having a high percentage of fireballs. There’ve been reports this weekend of some great Taurid fireball sightings, including the one from Eliot Herman in Tucson, above. Beautiful, yes? The peak of this shower is coming up this week. The South Taurids should produce their greatest number of meteors – and hence their greatest number of fireballs – between midnight and dawn on November 5, 2015. Try watching on the morning of November 4, too, and even on the mornings before that. The fireballs are flying!

How can you watch for Taurid fireballs? The good news is that the moon is now waning. Last quarter moon is early morning on November 3, according to clocks in North America. There will be a bright moon between midnight and dawn that morning, but the moon will be less and less obtrusive on the following mornings, leading up to the peak on November 5.

And remember these are fireballs we’re watching for. A little moonlight shouldn’t hinder them, as the photo above by Eliot Herman clearly shows.

In general, the South Taurids typically offer about 7 meteor per hour at their peak. However, the other Taurid shower – the North Taurids – always adds a few more meteors to the mix during the South Taurids’ peak night.

It’s the bright ones you really want to see, after all.

The Taurid meteor stream consists of an extremely wide roadway of far-flung debris left behind by Comet 2P Encke. When Earth travels through this belt of comet debris, bits and pieces of Comet 2P Encke smash into the Earth’s upper atmosphere to vaporize as rather slow-moving Taurid meteors (28 km/17 miles per second).

Apparently, the original Taurid stream has been perturbed by Jupiter into two branches: South and North Taurids.

Higher rates of Taurid fireballs might happen in seven-year cycles, and the last grand fireball display was in 2008. That could be good news for Taurid-watchers in 2015!