For Your Reference

The following section provides information that is applicable to a number of articles in this reference work. Included are a metric measurement and conversion table, geologic timescale, diagrams of an animal cell and a plant cell, illustration of the structure of DNA nucleotides, detail of DNA nucleotides pairing up across the double helix, and a comparison of the molecular structure of DNA and RNA.

METRIC MEASUREMENT

Definitions

Kilo = 1000

Hecto = 100

Deka = 10

Deci = 0.10 (1/10)

Centi = 0.01 (1/100)

Milli = 0.001 (1/1000)

Micro = 0.000001 (1/1,000,000)

Nano = 0.000000001 (1/1,000,000,000)

Conversions
To convert	Into	Multiply by
Acres	Hectares	0.4047
Centimeters	Inches	0.3937
Feet	Meters	0.3048
Gallons	Liters	3.7853
Grams	Ounces	0.0353
Grams	Pounds	0.0022
Hectares	Acres	2.4710
Inches	Centimeters	2.5400
Kilograms	Pounds	2.2046
Kilometers	Miles	0.6214
Liters	Gallons]	0.2642
Meters	Feet	3.2808
Miles	Kilometers	1.6093
Ounces	Grams	28.3495
Pounds	Kilograms	0.4536
Pounds	Grams	453.59

ERA	PERIOD		EPOCH	STARTED (millions of years ago)
ERA	PERIOD		EPOCH	STARTED (millions of years ago)	Cenozoic: 66.4 millions of years ago–present time	Quaternary		Holocene	0.01
Pleistocene	1.6
		Tertiary	Neogene	Pliocene				5.3
			Neogene	Miocene				23.7
Paleogene	Oligocene		36.6
	Eocene		57.8
	Paleocene		66.4
Mesozoic: 245–66.4 millions of years ago	Cretaceous		Late	97.5
			Early	144
					Jurassic		Late	163
							Middle	187
	Early	208
	Triassic		Late	230
			Middle	240
			Early	245
	Paleozoic: 570–245 millions of years ago	Permian		Late	258
				Late	258	Early	286
Carboniferous				Pennsylvanian	Late	320
		Mississippian	Early				360
		Devonian					Late	374
				Middle	387
Early				408
Silurian		Late	421
Silurian		Early	438
Ordovician		Late	458
		Middle	478
		Early	505
Cambrian		Late	523
		Middle	540
		Early	570
Precambrian time: 4500–570 millions of years ago				4500