Mysteries of Nature 

There are many mysteries in nature.

Mysteries are things we don't understand, such as how the Egyptian pyramids were built.

In fact, we are surrounded by mysteries.

What we know about the world seems like very little.

Scientists tell us that what we see in the universe is only a small part of what is there.

The rest is invisible, including dark matter and dark energy.

These two unknowns make up around 95% of the universe.

Evidence for their existence comes from their effects on what we can observe, such as the motion and positions of distant galaxies.

Yet, though we know very little, we are able to build airplanes and communicate with smartphones.

In some ways we humans are very smart, or at least we think we are.

We still need to face big issues, like climate change, and that is going to be a huge challenge.

The challenge for humans will be our ability to adapt to our changing environment.

What about other forms of life?

How do they adapt?

Seasonal variations, for example, can be one of the greatest challenges for animals to overcome.

Overcoming such challenges is a great achievement, but hardly easy.

Some birds migrate thousands of kilometers each year to deal with seasonal changes.

These migrations are amazing.

Birds don't carry maps or compasses, yet they know where to go.

They have developed the ability to see the Earth's magnetic field.

This ability is a wonder of nature.

It takes advantage of the fact that the earth is like a huge bar magnet.

It has a north pole, which is positive, and a south pole, which is negative.

Somehow the birds are able to see this magnetic field and use it to their advantage.

How do birds know where to fly? They use the Earth's magnetic field.

And even the way birds fly together is amazing.

Many migrating birds fly in a V formation.

They do this to conserve energy.

In a V formation, birds can use the energy of the birds in front of them.

This energy comes from the air currents generated by the wings.

Conserving energy is necessary for the birds to survive the long journey.

How do the birds know this?

It's truly amazing how the birds know this.

Another amazing example of survival is the salmon.

Salmon spend most of their lives in the ocean, which is saltwater.

Yet, when it's time to breed, they do so in freshwater rivers.

Salmon can adapt their bodies to survive in both saltwater and freshwater.

When it's breeding time, they return to the same river where they were born.

it seems as if they have a built-in map that guides them for hundreds of miles.

Where do salmon spend most of their lives? in the ocean

Once they leave the saltwater, they don't eat.

They are determined to finish their journey, despite the many obstacles.

They swim against strong currents, jump over waterfalls and try to escape the claws of hungry bears.

Many die along the way, but enough of them survive to breed and produce the next generation.

Once they have laid their eggs, they die, havingcompleted their journey.

It seems that their purpose in life is just to reproduce.

What did they do after laying their eggs? they die

Migration takes animals to new, more favorable environments when the seasons change.

Some of these journeys are long and dangerous, along routes with no obvious landmarks.

The longest migration is that of the arctic tern.

It flies from pole to pole, twice a year.

If a tern achieves its average lifespan of 20 years, the distance it has flown will be equivalent to a journey to the moon and back.

A landmark is something easy to see and remember, like a river or bay.

Humans also migrate, but seldom if ever for seasonal variations.

Unfortunately, human migrations are often due to human activities.

Since the beginning of the 21st century, large scale migrations have become a global problem.

Millions of migrants have had to leave their countries and look for new homes.

Many have died along the way or lived as refugees in camps until they are admitted into a new country.

So the question remains as to how our global community will face these challenges.

Most human  migrations are due to human activities.