Deepest-forming rocks
On 19 May 2000, geologists from the University
of Queensland in Australia announced their
discovery of rocks on Malaita in the Solomon
Islands. These samples contained minerals that
only form under very high pressures, including
microdiamond and majorite – a form of the
mineral garnet that is rich in silica. Examining
the structure of the majorite crystals, the team
concluded that they had experienced pressures
of up to 23 gigapascals, around a quarter
of a million times greater than atmospheric
pressure at the surface, indicating that the
rocks originated 400–670 km (248–416 mi)
underground.Greatest eruption (by pumice ejected)
The amount of ejecta in the Taupo eruption, which
took place in New Zealand in around ce 186, has
been put at 30,000 million tonnes of pumice.
It flattened an area of 16,000 km^2 (6,200 sq mi).Most common rock type at the surface
of the continental crust
Approximately 75% of Earth’s continental
crust has sedimentary rocks at its surface.
Usually present as a thin veneer over igneous
and metamorphic rocks, these sedimentary
rocks include sandstone, mudstone, chalk and
breccias. They formed when small particles
became buried over time and were subjected
to great pressures. Erosional and tectonic
forces can expose them on the surface again.
The most common sedimentary rocks are
mudrocks, which include mudstone, shale and
siltstone and are made up of particles smaller
than 0.0625 mm. They account for around 65% of
all sedimentary rocks on Earth, and possibly up to
80%. Mudrocks consist mainly of clay minerals
and most of them formed at the bottoms of
oceans and lakes. Dead organic material, mixed
with the original sediments, is responsible for the
occurrence of fossil fuels in rocks such as shale.Youngest Moon rocks
A type of volcanic basalt, Moon rocks begin to
form in the dark lunar maria (seas). The most
recent examples date back some 3.2 billion
years – making them not dissimilar in age
to the oldest dateable rocks on Earth. Lunar
samples measuring 382 kg (842 b) from the
Apollo missions have been returned to Earth.Hard Rock
EARTH
MOST RECENT
FLOOD BASALT
ERUPTION
When a huge volcanic
eruption covers large
areas of land or sea
floor in basalt lava,
the result is known
as a “flood basalt”. In
1783, Laki – a system
of volcanic fissures
in Iceland – began
exploding, in one of
only two episodes of
flood basalt eruption
in historic times.
For eight months, it
emitted some 15 km^3
(3.5 cu mi) of lava,
along with 122 million
tonnes (134 million
tons) of sulphur
dioxide. The effects
of this gas at least
partially caused the
devastatingly cold
winters of 1783–
and 1784–85 and the
cool summer of 1784.Granite makes up most of Earth’s crust and is found on every continent.
But to date, no trace of it has been found anywhere else in the Solar System.In 2005, researchers at the
Bayerisches Geoinstitut in
Bayreuth, Germany, produced
an aggregated diamond
nanorod (ADNR) that is 11% less
compressible than diamondHardest substance
on the Mohs scaleIt took 14 years for
400 men to carve
the likenesses of four
US presidents into the
granite at Mount Rushmore
in South DakotaMount Rushmore noses
(length):Mount Rushmore eyes
(width):If it was a whole figure, the
likeness of George Washington
on Rushmore would stand:20 ft (6 m)
11 ft (3.35 m)
465 ft
(141.7 m)The Earth’s crust is made
of 64.7% igneous,
7.9% sedimentary and
27.4% metamorphic rocksLARGEST MARTIAN METEORITE
The Zagami meteorite, which weighed
approximately 40 lb (18 kg), making it around
6.5 times heavier than a house brick, landed
on Earth on 3 Oct 1962. It fell into a field near
the village of Zagami in Nigeria, about 10 ft (3 m)
away from a farmer who was attempting to clear
cows out of his corn field and who was buffeted
by the blast. He subsequently discovered the
extraterrestrial rock in a 2-ft-deep (0.6-m) crater.
An estimated 32 meteorites from Mars have
landed on Earth to date.LARGEST...
Meteorite
A block 9 ft (2.7 m) long by 8 ft (2.4 m) wide,
estimated to weigh 130,000 lb (59 tonnes), is
the largest known meteorite. It was found in
1920 at Hoba West, near Grootfontein in Namibia.
The largest lunar meteorite is Kalahari 0 09,
with a mass of 13.5 kg (29 lb 12 oz). It was found
in Kalahari in Botswana in Sep 1999. Around
50 meteorites on Earth originated from the Moon.Stone run
During the last ice age, intense freezing followed
by thawing gave rise to accumulations of
boulders known as “stone runs”. Princes Street,
located north-east of Stanley in the Falkland
Islands, is a stone run measuring 4 km (2.4 mi)
long and 400 m (1,312 ft) wide. It consists of
thousands of boulders of hard quartzite rock,
mostly 0.3–2 m (11 in–6 ft 6 in) across.Anorthosite body
An igneous rock, anorthosite consists mostly of
the mineral plagioclase feldspar. On Earth, there
are two types of anorthosite – Archaean and
Proterozoic – which formed 3.8–2.4 billion years
ago and 2.5–0.5 billion years ago, respectively.
They are thought to have formed in underground
magma chambers where partially melted mantle
material separated into denser “mafic” minerals
and lighter “felsic” ones. A body of anorthosite,
estimated at 20,000 km² (7,722 sq mi), underlies
an area north of Lake St John in Quebec, Canada.Craton
This term describes large parts of continental
crust that are stable and have remained relatively
unmodified by plate tectonics since the end
of recambrian he t P period, 542 million years
ago. They are normally located in the interior
of continents and contain some of the oldest
rocks on Earth. The North American craton is the
largest, covering around 70% of the continent.
It was formed some 2 billion years ago by the
collision of several smaller microcontinents.Q: What is the difference
between lava and magma?
A: Magma is molten rock below
the Earth’s surface. When it erupts
above ground, it is called lava.
In^ 1996, the Mars
Global Surveyor
spacecraft^ took
off,^
carrying a grain of the
Zagami meteorite. In time,
the craft will smash into
Mars, thereby returning
the fragment to its
place of origin.