GLOSSARY – E

GLOSSARY – E

by: Charles O’Dale

EJECTA
Solid, liquid and vaporized material ejected from an impact crater during its formation.

  • Distal  – Impact ejecta found at distances greater than 5 crater radii from the rim of the source crater;
  • Proximal – Impact ejecta found up to 5 crater radii from the rim of the impact crater;
  • Blanket – A generally symmetrical apron of ejecta that surrounds an impact crater; and
  • Curtain – Impact-excavated clasts ejected ballistically on parabolic trajectories combine into a cone-shaped curtain, the ejecta curtain, expanding outward from the crater rim and turning into the ejecta blanket around the crater.

[see – EJECTA]

ELASTIC REBOUND
Part of a theory explaining the forces that cause earthquakes. In impact cratering , elastic rebound describes the readjustment of the highly compressed floor of the transient cavity in the modification stage.

ELEMENTS – (source)

Elements are grouped according to their preferred host phases into LITHOPHILE (silicate loving), SIDEROPHILE (iron loving), CHALCOPHILE (sulfur loving), and ATMOPHILE (gas loving). Courtesy APOD

EUCRITE
A common class of achondrite meteorites composed of pigeonite and plagioclase. These meteorites formed as basaltic flows on a parent body, probably asteroid 4 Vesta. (Data collected by NASA’s Dawn Mission, in orbit around Vesta from 2011-2012, strengthed the association between Vesta and eucrite meteorites.)

EXCAVATION STAGE
The crater excavation stage (Melosh, 1980) overlaps somewhat with the compression stage and involves two processes:

  • upward ejection (spalling) of large near-surface fragments and smaller ejecta (ejecta curtain);
  • subsurface flow of target material to form the transient crater.

[see – CRATER CLASSIFICATION – Complex crater]
[see –  CRATER FORMATION]
[see – CRATER IDENTIFICATION]

EXTINCTION vs IMPACT
Extinction of many groups of organisms at a particular time by environmental catastrophe related with collapsing ecosystems. There are strong indications that some mass extinctions may be caused partly or completely by large asteroidal or cometary impacts.
[see –  EXTINCTIONS]