Content of Earth-impacting meteors over time

[jim mcnamara]

http://www.nature.com/articles/s41550-016-0035
Rare meteorites common in the Ordovician period

About 466 million years ago, a large asteroid had a really bad day, and
fragments from the collision have dominated meteorites impacting the Earth
since that time.

Circa 1 billion years ago there was a similar event involving the asteroid Vesta
which dominated the fragments impacting Earth. Back then.

I guess you could call it: "meteor weather" on a huge time scale.

phys.org article:
https://phys.org/news/2017-01-big-picture-meteorites-giant-space-collision.html

 

[davenn]

Hi @Jim

Somehow I missed this post you did, way back then

Interesting articles. I find it fascinating that most falls way back then were chondrites
of one type or another where the falls in the last say 100,000 yrs appear to be more nickel/iron
in composition, at least going by what has been seen to fall and by what has been found and identified.

My own collection the ratio would be ~ 70%/30% nickel/iron to what ever else ( chondrite etc).
This is not a personal preference towards Ni/Fe ones, to the contrary, I find the others are more
difficult to source. Yet Wiki etc state that ~ 87% of all meteorites found are in the chondrite class.

just some examples from my own collection...

Iron.

CLASS: Med Octahedrite, 111CD
Western Australia ( State), Australia

Iron

CLASS: Iron, Fine octahedrite, IVA
Sweden

Ordinary Chondrite
CLASS: Stone, Ordinary chondrite (H5)
Morocco reg., NW Africa

Chondrite
complete fragment with fusion crust
CLASS: Stone, Ordinary chondrite (H5)
Mali

and very new to the collection, I finally got a couple of Pallasites
Class: Pallasite (Stony Iron)
Kansas, USA

for the above one ...

from Wiki
Notable pallasite finds[edit]
Although pallasites are a rare meteorite type, enough pallasite material is found in museums and meteorite collections and is available for research. This is due to large finds, some of which yielded more than a metric ton. The following are the largest finds:

Brenham, Kansas, United States. In 1890 the find of about 20 masses with a total weight of 1,000 kilograms (2,200 lb) around the shallow Haviland Crater were reported. More masses were found later, including one of 454 kilograms (1,001 lb) from a depth of 5 feet (1.5 m), the total amounting to about 4.3 tonnes (4.2 long tons; 4.7 short tons). A piece of 487 kilograms (1,074 lb) is in the Field Museum of Natural History, Chicago. In 2005, Steve Arnold of Arkansas, USA, and Phil Mani of Texas, USA, unearthed a large mass of 650 kilograms (1,430 lb) and in 2006 several new large masses [11][12]
Cheers
Dave