Esta terra é nossa.

Because terra is a feminine singular noun.

In Portuguese, words that go with a noun usually have to match its gender and number:

• este = masculine singular
• esta = feminine singular
• estes = masculine plural
• estas = feminine plural

Since terra is feminine singular, the correct form is esta.

So:

• esta terra = correct
• este terra = incorrect

For the same reason: nossa has to agree with terra, which is feminine singular.

Compare:

• nosso carro = our car
• nossa casa = our house
• nossa terra = our land

In this sentence, nossa means ours and still agrees with terra.

Terra can mean a few things in Portuguese, depending on context:

• land
• earth / soil
• the Earth (the planet), often written Terra

In Esta terra é nossa, the most natural meaning is land or this land.

So the sentence is not usually understood as This planet is ours unless the context clearly points that way.

Because esta already works as a determiner before the noun.

In Portuguese, demonstratives like este / esta / esse / essa normally go directly before the noun:

• esta terra
• esse livro
• aquela casa

You do not need a in front of terra here.

So:

• esta terra = correct
• a esta terra = only possible in other grammatical contexts, not as the basic subject here

Because Portuguese usually needs the verb ser here, just like English needs is.

• é = is

So the structure is:

• Esta terra = this land
• é = is
• nossa = ours

Without é, the sentence would be incomplete.

É is the third-person singular form of the verb ser:

• eu sou = I am
• você é / ele é / ela é = you are / he is / she is

Here the subject is Esta terra, which is singular, so Portuguese uses é.

Portuguese often uses the same possessive forms in slightly different ways.

• nossa terra = our land
• a terra é nossa = the land is ours

So nossa can mean:

• our, when it comes directly before a noun
• ours, when it comes after a linking verb like é

English changes the form:

• our
• ours

Portuguese often does not:

• nossa
• nossa

Context and sentence structure show the difference.

Because the sentence means This land is ours, not Our land is this one.

These are related but not identical structures:

• Esta terra é nossa = This land is ours
• Nossa terra = Our land

When Portuguese uses ser to link the subject to a description or identification, the possessive often comes after the verb:

• O livro é meu = The book is mine
• A casa é dela = The house is hers
• Esta terra é nossa = This land is ours

Yes, and in everyday Brazilian Portuguese, that is very common.

Traditionally:

• esta = this, near the speaker
• essa = that, near the listener or already mentioned
• aquela = that over there, farther away

But in modern spoken Brazilian Portuguese, essa often replaces esta in many situations.

So:

• Esta terra é nossa = correct, a bit more formal or careful
• Essa terra é nossa = also very natural in Brazil

It is more directly This land is ours.

Compare:

• Esta terra é nossa = This land is ours
• Esta é a nossa terra = This is our land

Both can be similar in meaning, but the structure is different.

The original sentence focuses on the land and says it belongs to us.

A simple approximate pronunciation is:

EH-sta TEH-ha eh NOH-sa

A few helpful notes:

• esta: the e is usually open, like eh
• terra: in Brazilian Portuguese, the rr is not like the English r; it is usually a throaty sound, somewhat like an h in many accents
• é: sounds like eh
• nossa: the o is usually open, closer to noh

So terra often sounds roughly like TEH-ha in many Brazilian accents.

In Portuguese spelling, rr and single r can sound different.

Between vowels:

• single r is usually a softer sound
• rr is a stronger sound

So:

• caro = expensive
• carro = car

Likewise, terra is spelled with rr, and that affects pronunciation.

By itself, it is grammatically neutral, but it can sound strong or emphatic depending on context.

Esta terra é nossa could be used in:

• a historical or political statement
• a patriotic slogan
• a discussion about ownership
• a dramatic line in a movie or speech

Using esta instead of essa can also make it feel slightly more formal or literary in Brazilian Portuguese.

Yes, but then the whole sentence would need to agree in the plural.

Singular:

• Esta terra é nossa = This land is ours

Plural:

• Estas terras são nossas = These lands are ours

Notice how everything changes to match the plural feminine noun:

• esta → estas
• é → são
• nossa → nossas