Matter is composed of atoms. An atom is the smallest particle into which an element can be divided and still have the properties of that element. There are many different types of atoms called elements. If a molecule is made of atoms from two or more elements, it is called a compound.

We now know that atoms are made up of three particles: protons, neutrons and electrons — which are composed of even smaller particles, such as quarks.

All matter, whether it is living or not, is composed of chemical elements; these are fundamental chemicals in the sense that they are what they are – they can’t be changed into another element. Each element is distinguished by the number of protons , neutrons , and electrons that it possess.

An atom is composed of two regions: the nucleus, which is in the center of the atom and contains protons and neutrons, and the outer region of the atom, which holds its electrons in orbit around the nucleus.

On the biggest steps in early human evolution scientists are in agreement. The first human ancestors appeared between five million and seven million years ago, probably when some apelike creatures in Africa began to walk habitually on two legs.

Eastern Africa

East Africa

Portuguese explorer Prince Henry, known as the Navigator, was the first European to methodically explore Africa and the oceanic route to the Indies.

Variation over time

There’s No Known Limit To How Long Humans Can Live, Scientists Say. Last October, scientists made a splash when they determined that on average, people can only live for about 115 years.

Today, some scientists are keeping the dream alive. These thinkers believe genetic engineering, or the discovery of anti-ageing drugs, could extend human life far beyond its natural course. Cambridge researcher Aubrey de Grey thinks there is no reason humans cannot live for at least 1,000 years.

Studies in the biodemography of human longevity indicate a late-life mortality deceleration law: that death rates level off at advanced ages to a late-life mortality plateau. That is, there is no fixed upper limit to human longevity, or fixed maximal human lifespan.

Shorter people also appear to have longer average lifespans. The authors suggest that the differences in longevity between the sexes is due to their height differences because men average about 8.0% taller than women and have a 7.9% lower life expectancy at birth.